astap.png ASTAP, the Astrometric STAcking Program, astrometric solver and FITS viewer




Download:

For MS Windows 64 bit:

For MS Windows 32 bit:


For Linux 64 bit:
           If you need a Linux 32 bit version, send me a request.
For Raspberry PI 3: 
For MacOS (i386) :
  Donations are welcome:

Index:



ASTAP introduction

ASTAP is a free stacking and astrometric solver (plate solver) program for deep sky images. In works with astronomical images in the FITS format, but can import RAW DSLR images or XISF, PGM, PPM, TIF, PNG and JPG  images. It has a powerful FITS viewer and the native astrometric solver can be used  by CCDCiel, APT or SGP imaging programs to synchronise the mount based on an image taken.

Main features:
  1. Stacking images including Dark Frame and Flat Field correction
  2. Native astrometric solver, command line compatible with PlateSolve2.
  3. Filtering of deep sky images based on HFD value and average value.
  4. Alignment using an internal star match routine,  internal astrometric solver or a call to a local version of Astrometry.net.
  5. FITS viewer with swipe functionality, deep sky and star annotation, photometry and CCD inspector.
  6. FITS thumbnail viewer.
  7. Results can be saved to 16 bit or float (-32) FITS file.
  8. Export to 16 bit PNG, 16 or 32 bit integer TIFF files, 16 bit PPM/PGM  files for best preservation or simple 8 bit PNG, BMP or JPEG.
  9. Mosaic building covering large areas using the astrometric linear solution WCS or WCS+SIP polynomial. 
  10. Background equalizing.
  11. FITS crop function.
  12. FITS header edit.
  13. Some pixel math functions and digital development process
  14. Available for 32 & 64 bit MS-Windows and Linux 64 bit., MacOS, Raspberry-Pi

Stacking of images:

Stacking of astronomical images is done to achieve a greater signal to noise ratio, prevent sensor saturation and correct the images for dark current and flat field. Additional imperfect images due to guiding, focus  problems or clouds can be removed.

This is a screen short of the stack menu. It contains several tabs for the file list and settings. File can be sorted on quality and values.The image can be visually inspected in the viewer by a double click on the file or using the pop-up menu.



Program requires FITS images or RAW files as input for stacking, but it can also view 16 bit PGM /PPM files, XISF files or  in 8 bit  PNG, TIFF or BMP files. For importing DSLR raw images  the program
DCRAW from David Coffin is used.
For stacking the internal routine compares the image star positions to align.

To uncheck/untick poor images there is an option to do that automatically. First check mark the option "After analyse untick worst images". Then press button "analyse images". The images will be analysed and the images with abnormal (outliers) HFD values or  "Number of star detected" will be unchecked. The adjustable factor used is the standard deviation represented by the Greek lower case sigma σ letter. To undo you have to check the images manually again, e.q. with the popup menu of the right mouse button.

For a normal distribution you could expect the following:

Confidence intervalProportion within
1σ68%
1.5σ87%
2σ95 %
2.5σ98.8%
3σ99.7%



Astrometric Solving:


ASTAP can be
used as astrometric solver to synchronise the telescope mount position with center position of an image taken with the telescope. Existing images can be solved to annotate, for photometry or the measure positions of unknown objects.

The ASTAP solver aims at a robust star pattern recognition using the catalog star coordinates in Equinox J2000. The solution is not corrected for optical distortion, refraction, proper  motion  of  stars and other minor effects all to be very minor.

The process astrometric solving is often referred to as a "plate solve". That was a correct description in the past, but in modern times there are no photographic plates involved in the process.


For the astrometric solution it can use either the internal solver or a local version of Astrometry.net. 



ASTAP is not:
A post processing software with advanced options like noise reduction and unsharp mask. It is only intended for convenient stacking of astronomical deep sky images.


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Program installation:

MS-Windows:

The installer will install it at c:\Program Files\astap . The single executable astap.exe can be used anywhere. 

Program works best using the internal alignment routine. For mosaics the internal solver routine will be activated or use local version of astrometry.net

Linux installation:

The program is provide as an debian archive astap_amd64.deb which can be installed with the default installer.  Executable will be placed in /opt/astap

Program works well using the internal alignment routine. For mosaics the internal solver routine will be activated or use local version of astrometry.net


Program operation, stacking astronomical images:

The purpose of the stacking routine is to combine astronomical images to reduced noise and to flatten the image.

 Ideally you should have collected

Only light frames are essential.

The automatic stacking process in ASTAP goes through the following steps:
  1. The flats will be combined to an average and the combined average flat-darks will be subtracted to  have a near ideal presentation of the vignetting called the master flat frame.
  2. The combined dark frames called master dark will be subtract from the light frames to extract the pure deep sky signal.
  3. The combined light frames, dark compensated in 2) will be flattened by dividing it by the master-flat resulting in the final deep sky image. Prior to this a small 2x2 or 3x3 median filter is applied  the master flat to reduce noise.

Operation of the stacking program

Start the ASTAP program. (In MS-Windows astap.exe, in Linux astap)


Call up the stack window using the Σ button.

a) Select frames
In tab
images, dark, flats, flat darks, select the select the images, dark, flats, flat darks (bias) frames. In most cases you could select all frames in tab images. The program will move the fames to the corresponding tab during analyse.

b) Analyse and remove bad frames
I
n tab images (for the light frames), press analyse and remove manually any poor image. Poor images can be detected by a too high HFD (Half flux diamater stars), low number of stars or high background value( by clouds) .
Loss of tracking could result in too low HFD value. If required inspect each image by double on the file name. The list can be sorted by clicking on the corresponding columns. Using the pop-up menu selected bad frames can be renamed to *.bak for deletion later.

c) Set parameters in tab stack method
In tab stack method select the stacking method, average or sigma-clip-average. For OSC camera images  select "Convert OSC images to colour". Select the correct Bayer pattern (4 options). Test the required pattern first in the viewer with a single image. The source images should be raw (gray)  without colour produced by  astronomical camera's.

d) Set parameters in tab alignment
Leave this to the default star alignment. Leave the parameters "star alignment and astrometric alignment at default values.

e) Classify by check marks
Leave all check marks 
initially unchecked. These classify options can be used later to combine the correct darks and flats and to stack several image series in one operation.

f) Press the stack button.
The darks and flats & flat-darks will be combined in a master dark and master flat frame. Then the program will combine the light frames to the final image and save it automatically. This will take some time.

g) Export
Use the resulting FITS file. Crop the sides if required using the pop-up menu. Equalise the back ground if required using the tool in tab pixel math. Export as stretched JPG or 16 bit bit stretched TIFF.  The stretched export follows the gamma and stretch setting of the display.


  


All the program settings and file selections will be save by leaving the program or click on the stack button.

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Mosaic building

This is possible with the internal astrometric solver or local version of Astrometry.net. The reference of each pixel is the astronomical position. So stacking is not done against a reference image but against an position array set by the first image. If the oversize is set from the default 100 pixels to a  large value lets say 2000 pixels, the array is on all sides 2000 pixels larger then  the first image.  If the first image is 2000x1500 pixels, the stacking array will be 6000 x 5500 pixels large. So any following image will be placed in this 6000x5500 pixel array.  If the images are taken from different areas of the sky, the stacking will result in a mosaic as long the proceeding images are within this 6000x5500 pixels.


Here a suggested work method:
  1. Stack the tiles separately using method SIGMA-CLIP-average and use for the alignment the internal STAR alignment method.  Inspect the resulting tiles and crop them if required. You can also crop them later automatically with "Mosaic skip outside pixels" Do this for each color separately if you have separate files.
  2.  Stack the resulting tiles  using method MOSAIC (with oversize set at 2500 if the original tile images are 2328x1760 pixels) and select astrometic alignment using internal or the local Astrometry.net for solving. (option --downsampling 2)
  3. Crop the stacked result to about 5000x5000 pixels. 
  4. If required, apply the median-equalising filter under tab Pixel Math to equalise darker areas.
  5. If you have seperate colours, check-mark the option classify by filter and stack the 3 seperate mosaics to colour.
  6. Adjusted the stretch range and save as JPEG, 90% quality.
Here an example mosaic x 4 of M31 made with ASTAP:





Here an example of a mosaic build of DSS images:

The size can be reduced by a crop function (right mouse button) later. Making the oversize too large could result in memory overload.

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The stack menu:




For a generic description how to stack see Program operation, stacking astronomical images

Stack multiple objects: Several objects can be stacked in one run. If the classify-by-object is check-marked, the program will stack all objects and save the results using the available darks and flats.

Analysing and removing of the bad ones: Before stacking the images can be analysed with the analyse button. Images with a high HFD value are most likely unsharp and can be inspected in the viewer by double click on the filename. The file can be renamed to *.bak by the pop-up menu to be removed later. Images with a high background indicating clouds or twilight should be removed/renamed to *.bak.

Sorting: Images can be sorted on any of the columns. For example if you click on HFD, the images will be sorted on HDF. You could then remove the images with the highest value or inspect them by double click on the file name.

Dark classification: If classify by exposure time and/or exposure time is check-marked the program will automatically select the correct darks or master dark. So it is possible to keep several dark files check-marked in the darks tab and the correct master dark will be selected automatically.

Colour stack and Colour filter classification: If
the classify-by-filter is check-marked, the stack routine will combine the available filters to a RGB image. If only Red + Green +Blue image are available they will be combined in a RGB image. If Luminance images are available it will first stack the RGB colors and then apply a most-common-filter and Gaussian blur on the RGB result. Finally the luminance image is coloured with the RGB result. The filter factor should be set typically near 20.

For nebula you could combine RGB or LRGB. If a luminance filter is detected the LRGB mode is used. First the RGB is combined, stars are removed using a most common filter, the image is then blurred with a Gaussian blur and and the colour is then applied luminance channel. Star colour is lost with this process. The filter names can be set in tab alignment

To record star colours use RGB only.

It could be better to stack in two steps. First prepare the Red, Green, Blue and Luminance stacks. Then run a stack again with the 
Red, Green, Blue and optional Luminance. Or if you could revisit the produced interim results in the RESULTS tab en copy them to the IMAGES tab using the pop-up menu. You could try different colout factors.

Image file names containing "_stacked" will be
un-checked by default to prevent stacks by accident are re-used. If required, just select the file and check-makr it again.

Organising images, darks, flats and flat-darks: Images placed in the first tab will be organised based on the FITS header keyword
IMAGETYP. So as soon you click on the image analyse button, dark and flats and flat darks/bias images will be move to the corresponding tab.

Keyword modification: The pop-up menu has option to update a keyword of multiple files if required.

OSC images (one shot colour images): To import raw files from digital camera, ASTAP can execute the command line program DCRAW from David Coffin. This program is included with the ASTAP Windows version. For Linux install by e.g. "sudo apt-get install dcraw.  See import
The stacking of  OSC images works best if you start with raw image before it is converted to colour. The raw colour images look mono, but the program will convert them later in the stacking process. There are 4 different Bayer pattern. They are identified as 00, 1,0, 0,1, 11 and can be set in
the stack tab "stack method". Try emperish which will result in the correct colours. Load a raw image in the viewer and convert it using tools menu option "convert bayer matrix"(CTRL+0). If the colours are not correct, just hit CTRL-Z to recover and try an other bayer pattern setting in stack tab "stack method"

Select for OSC image 2x2 mean for flats, see tab stack method. This will prevent any interfering patterns due to the 2x2 Bayer matrix.

Power down option after completion:  If stacking takes a long time you could activate this option and the program will be power-down the computer after completion.


Results tab.

The stack results are reported in the results tab. By a double click they can be viewed the viewer. The number of files and exposure times are given. With the pop-up menu it is possible to copy the image file path to the clipboard for use in a file explorer.
 


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Stack method


Master flat:         Typical setting 2x2 mean

Darks filter:         Typical setting, apply Gaussian blur of 3.0 below
the noise standard deviation σ =2.5. For noise  CMOS sensor you could select restore hot pixel above σ.

Stacked image:    Best option is "Sigma clip average". For only 2 or 3 images or when you are in a hurry "average"will do.

Raw one shot colour images (OSC):
 
RAW images of  DSLR cameras /One shot color cameras are monochrome and have to be converted into colour images (after applying darks and flats). This converson is called demosaic or debayer. First set Bayer pattern correctly by loading a raw image (grayscale) in the viewer and try one of the bayer patterns till the image colours match in viewer. If not hit CNTRL-Z to undo and try a different Bayer pattern.

There are several methods to convert (demosaic/debayer ) the raw image  to colour:
  • AstroC, colour for saturated star, as bilinear method but for saturated stars the program tries reconstruct the star colour.
  • AstroM, white stars, as bilinear method but if there is an unbalance between the 4 red, 4 blue or 2 green pixels it uses luminance only. Effective for unsampled images and stacks of a few images only. Star colour is lossed if undersampled but star will become white.
  • Bayer drizzle, no interpolation but large amount of images are required. The raw image is coloured depending on the Bayer pattern and used in stacking. When sufficient images are stacked and there is some natural drift each position will get red, green or blues values averaged. The sky background and transparancy should be stable while imaging to achieve a good stacking result.
  • Malvar-He-Cutler 1), advanced method for interpolation but less effective for undersampled OSC images. Background noise is lower.
  • Super-pixel, This simple and method reduces the image size to half. Super-pixel could be used if the images are near or over-sampled. If your using a H-alpha filter in front of an OSC camera, by using the super-pixel de-mosaic method, you could just remove the green and blue signal to create a noise free red image and then convert it to mono. This makes processing simpler. There is no interpolation between the R,G,G and B pixels, so any noise from G an B pixels can be separated from the red.

What to select:

The background colour noise can be removed with option "Background colour removal" in the pixel math tab of the stacking menu.

The DSLR OSC images will be automatic converted to FITS files by the DRAW program included.


Oversize: This could be 0, 100 or larger. This overlap was introduced to show overlapping images. If you don't want a black Set this a zero if If you have accurate mount you could se for mosaic's   If  you want to  make a 2x2 mosaic, the overlap should at least the width of  the images.

The settings will be saved automatically if your either exit the program or start a stack.

There are test buttons for the dark and mean filter. They will be applied on the image in the viewer. For CMOS darks it is recommend to select restore hot pixel above 
σ is 3 or 2.5.

Typical cold CMOS master dark:

Application of Gaussian blur under σ is 3 and option "restore hot pixel". The hot pixels above σ  is 3 are restored:

Gaussian blur without hot pixel restore:



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The alignment menu:

For alignment there are three options, internal star alignment,  native astrometric solver or a local version of Astrometry.net. For mosaic building you have to use the internal astrometric solver or Astrometry.net.


 Internal star alignment



This internal star matching alignment is the best and fastest option to stack images. It is not suitable for mosaics. No settings, fully automatics alignment for shift in x, y, flipped or any rotation using the stars in the image. It will work for images of different size/camera's with some limitations.

The program combines four close stars into an irregular 2D tetrahedron or kite like figure (and compares the six irregular tetrahedron dimensions with irregular tetrahedrons of the first/reference image. It selects at least the six best matches and uses the centre position of the irregular tetrahedrons in a least square fitting routine for alignment. 

There is only two settings relevant but normally you don't have to change them.

The following image shows the irregular tetrahedrons used in an astronomical image:


Background info: A irregular tetrahedron (or triangular pyramid) drawn from 4 star positions has six edges. The five shortest edges are divided by the longest side to scale them independent of the image scale.  The final irregular tetrahedron definition is then the scaled length of the five edges, the centre mean position and the pixel length of the longest edge. For tetrahedron matching the scaled five edges are used. There scaled lengths will be independent on the image scaling. This will give a number of tetrahedron matches. From the matching tetrahedrons list,  the not scaled sixth edge is used to calculate the mean and 
standard deviation and outliers of more then 3 * σ are removed. (three times the standard deviation). From the remaining list of tetrahedrons, the central mean positions are used for LSQ fitting in two dimensions.

For each star, the  tetrahedron is constructed from the nearest stars. Some edges could overlap. Duplicates are removed. Duplicates could occur from four close but lonely stars. The tetrahedron selection can be demonstrated by the "draw tetrahedrons"button in the alignment tab. You could reduce the number of tetrahedrons drawn by the setting"maximum number stars used".

The process is described here
Background info, how does the ASTAP astrometric solving works internally


Astrometric alignment.

There are two option for astrometric alignment. The internal solver is quicker and adequate for most stacking. If somehow the alignment is not working it is possible to use a local version of  "astrometry.net"

   Internal astrometric solver (plate solver). The works with the same four star tetrahedrons as for the Star alignment option. The tetrahedrons are compared with the G17 star database (to be installed in the program directory). It has the following settings:

The internal plate solver works best with raw unstretched and sharp images of sufficient resolution where stars can be very faint. Exposures 5 to 300 seconds. Heavily stretched or photo shopped images are problematic. 

For those are interested:  
Background info, how does the ASTAP astrometric solving works internally



Astrometry.net local solver:

   Some guidelines for astrometric stacking using astrometry.net:


Manual alignment.

This option allows alignment of the images based on a single star, asteroid or comet. If this option is activated, the list of images in the image tab turns red. Double click on each image in the list and click on the star/comet of asteroid to be used as reference. This object is then marked with a little purple circle. The position will be auto centered. (and the X,Y position will be added to the list) A poor lock is indicated by a square. If so try again till it is a circle. If all images in the list are turned green, so contain a value, then click on the stack button.

For objects which are moving in the sky, select the stack option "average" and not option "sigma clip".



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Pixel math.

 Several options including background equalising.



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Additional functionality:


Viewer:
The viewer has a preview function. After opening select Preview FITS files. The preview is displayed in the ASTAP viewer. The current zoom and position is maintained so you could study the corner of a series images on image quality.

The file open menu with preview selected:



For JPG, PNG or RAW files it is possible to add the object position using the deepsky database. Double click on RA position in viewer and enter the object name. The position will be retrieved from the database. This position will be used for the solver.



Thumbnail viewer for FITS files


ASTAP has a FITS thumbnail viewer (ctrl-T). This could be useful to browse your FITS files. By clicking on the thumbnail it will be opened in the viewer. With a right mouse button click some options are available as changing directory, copy, move, rename or rename to *.bak.

The thumbnail size is depending on the form size. Make it larger, the thumbnails will follow. Thumbnails are organized in 3*X. So the thumbnails are pretty big by purpose. The images are fully loaded in memory so it will consume some memory and time. So don't try get thumbnails of 400 images.




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ASTAP viewer screen shot:




Deep sky annotations   

If the image is solved, it is possible to add deep sky annotations. See pull-down menu TOOLS:



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Star annotation and photometry

A second menu option is to annotate the stars and auto calibrate the program for photometry. This can be done either by the G17 or G18 star database (G- magnitudes) or if you replace them by the G16. This database contains the calculated Johnson-V magnitudes.

Below, the image is 1) solved, 2) auto calibrated (using the G16)   The cursor is at a star and based on the flux of all know stars, the star Johnson-V mangitude is estimated to be 16.1. The stars are marked with the Johnson-V magnitude and  Bp-Rp color indication,



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CCD inspector

ASTAP has a CCD inspector under tools for median HFD value and Tilt measurement.  This will quickly show any focus problem in the corners:. The squares are 5 times the HFD value. 




View menu

This menu has the following options:
Export FITS data to a spreadsheet:

To analyse the relation between the HFD value, focuser position, temperature and altitude it is possible to copy the data from a FITS image list to the operating system clipboard.

Just select a number of images, click on the analyse button. Then select all relevant files and copy the data with right mouse button. Then copy the data into a spreadsheet for analysis.





Here and example of the result in a spreadheet:



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Text entry option:

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Inspection on pixel level:


Batch conversion:

With the batch routine several FITS image can be "astrometric solved".   Raw images of OSC (color) sensors using a Bayer matrix can be converted to color.


 
Command line options:

ASTAP can imitate PlateSolve2 and add the plate solution to the FITS header. Also PNG, JPEG, TIF, BMP files can be plate solved if an estimate of the center position is given. See  Usage as astrometric solver and command line options:.


There is a big variation in FITS file keywords and usage. If your FITS file is not read, please send me the file for testing.






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Background equalization tool:




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Local viewer tools:


Where to find:   pop-up menu of the viewer.

Objective: To local improve the stacked image.

Usage: Select the area while holding the right mouse button down. Select the local option.




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Usage as astrometric solver and command line options:

For images in the viewer:

The simplest way to solve an image is just to load an image in the viewer and hit the solve button. Some settings are available in the ∑  menu under tab alignment. 


The solution will be added to the fits header and center of the image will be displayed in the log ∑  menu. Click on the save button to save the FITS file with the solution. With the solution, the status bar will show the astronomical position of the mouse pointer.

Conditions required for solving:

The internal astrometric solver works best with raw unstretched and sharp images of sufficient resolution where stars can be very faint. Heavily stretched, saturated or photo shopped images are problematic.  It requires minimum about 30 stars in the image to solve. Images containing of a few hundred stars stars are ideal. For star rich images, the program will reduce the detection limit to limit the number of stars. This will only work for unstretched images where brighter stars have a greater intensity then fainter stars. So ASTAP requires three star dimensions for solving. The x, y coordinates and intensity. Oval stars due to tracking errors or severe optical distortion will be ignored and solving could fail.

Check list for successful solving with ASTAP:
  1. Estimated center of  image should be entered/available in the viewer α and δ input or passed by command line.  For FITS this is normally automatic set.
  2. Field of view of the camera should be available. This is the height of the image in degrees. See ∑ window, tab alignment, group-box astrometric settings. For FITS images this is normally automatic calculated.
  3. Image height in pixels after subsampling should be somewhere between 1000 and 3000. If it is higher set subsample at 2 or maybe 3.
  4. Search radius should be set large enough. See ∑ window, tab alignment, group-box astrometric settings.  You could set this at 30 or larger up to 180.
  5. Stars in the image should be pretty round. You could verify the star detection by the CCD inspector or by  the "test button to show tetrahedrons" in the  ∑ window, tab alignment). All bright stars should be detected.
  6. About 30 stars or more should be visible in the image. They can be very faint, barely visible in the noise.
  7. For images filled with stars, only a few stars should be saturated. The total exposure time could be hours as long it is possible to separate the brightest stars from the faint by intensity.
  8. For bayered images (OSC cameras) or  large images use the x2 downsample option. See ∑ window, tab alignment, group-box astrometric settings. 
  9. The maximum number of stars to use should be defined. Typical set at 500. See ∑ window, tab alignment. 
  10. Tetrahedron tolerance should be defined. Typical set at 0.005. If you expect optical distortion set it higher.  See solver window, tab alignment.  Solving of wide field images covering a field of 10 degrees or more will most likely fail. 
  11. For some failures you could force in ASTAP the option "small steps (-speed)" for more reliable solving. The reliability will be very high but speed two or three time slower.
Above options can be set using the command line.

Command line, ASTAP style

The program can be executed using command line options to solve images astrometric . E.g.  ASTAP -f  home/test/2.fits   -r 30 

The program will accept FITS files, JPG, PNG, BMP or TIF files.



ASTAP astrometric solver command line
The FOV, RA,DEC options are intended for none FITS files.
Not required for FITS files having the values in the header.
command
parameter unit remarks
-h

help info
-help

help info
-f file_name
File to solve astrometric.
-r radius_search_field degrees The program will search in a square spiral around the start position up to this radius *
-fov field_height_of_image degrees Optional. Normally calculated from FITS header.  *
-ra center_right_ascension hours Optional start value. Normally calculated from FITS header.
-spd center_south_pole_distance
(dec+90)
degrees Normally calculated from FITS header *
The declination is given in south pole distance, so always positive.
-z down_sample_factor
1,2,3,4 Down sample prior to solving. Also called binning. *
-s max_number_of_stars
Limits the number of star used for the solution. Typical value 500. *
-t tolerance
Tolerance used to compare tetrahedrons. Typical values 0.003 to 0.007. *
-speedmode
slow / auto"slow" is forcing small search steps to improve detection. *
-update

Update the fits header with the found solution *
-annotate

Produce a deep sky annotated jpg file with same name as input file extended with _annotated *
-tofits binning 1,2,3,4,6,8 Produce binned FITS file from input png/jpg *







* Defaults can be set in the program. Shortcut CTRL-A, tab alignment
        

Preference will be given to the keyword values in the FITS header. Front-end programs should provide access to -z and -r options.

Typical command lines:

astap.exe -f image.fits  -r 50 -z 2

astap.exe -f c:\images\image.png  -ra 23.000  -spd 179.000  -fov 1.3  -r 50  -z 2


For most FITS files the command line can be short since telescope position and field of view can be retrieved from the FITS header. If a FITS file is not available, preference is a non lossless image format like .PNG or .TIFF or RAW like .CR2.  If possible in 16 bit or original 12 bit format. Not stretched or saturated, as raw as possible. For formats other then FITS the RA,DEC position and -fov (image HEIGHT in degrees !!) should be added.

Blind solving performance for a 90 degrees offset:

ASTAP blind solver performance. Solving a 50 seconds exposed monochrome image of M24, 2328x1760 pixels covering a field of 1.75 x 1.32 starting 90 degrees more north at position 18:17, +72d 00 



Maximum stars set Tolerance setAstrometric solving  time
5000.005147 sec.
2500.005103 sec
1500.00592 sec
1000.00570 sec



Reducing the "maximum number of stars to use" will result in a faster solving but also an increased risk of solve failure.


In command line mode the program produces two output files at the same location as the input image. A .wcs file containing the solved FITS header only and an INI file using the standard FITS keywords.

Example of the INI output file:

PLTSOLVD=T                                     // T=true, F=false
CRPIX1= 1.1645000000000000E+003               
// X of reference & centre pixel
CRPIX2= 8.8050000000000000E+002                // Y of reference & centre pixel  
CRVAL1= 1.5463033992314939E+002                // RA (J2000) of the reference pixel [deg]                   

CRVAL2= 2.2039358425145043E+001                // DEC (J2000)of the reference pixel [deg]                   
CDELT1=-7.4798001762187193E-004                // X pixel size [deg]
CDELT2= 7.4845252983311850E-004                // Y pixel size [deg]
CROTA1=-1.1668387329628058E+000                // Image twist of X axis [deg]
CROTA2=-1.1900321176194073E+000                // Image twist of Y axis [deg]                
CD1_1=-7.4781868711882519E-004                 // CD matrix to convert (x,y) to (Ra, Dec)  
CD1_2= 1.5241315209850368E-005                
// CD matrix to convert (x,y) to (Ra, Dec)                                   
CD2_1= 1.5534412042060001E-005                 
// CD matrix to convert (x,y) to (Ra, Dec)             
CD2_2= 7.4829732842251226E-004
                // CD matrix to convert (x,y) to (Ra, Dec)

The reference pixel is always specified for the centre of the image.

If the ASTAP is command-line executed in MS-Windows, it will be shown by a small ASTAP tray icon on the right side of the status bar. If you move the mouse to the ASTAP tray icon, the hint will show the search radius reached. To refresh the value move the mouse away and back. 

If the search spiral has reached a distance more then 2 degrees from the start position then a popup notifier will show the actual search distance and solver settings:

  1. The first line indicates the search spiral distance (8) from the start position and the maximum search radius (90)
  2. The image height in degrees. 
  3. Downsample setting and the input dimensions of the image to solve. 
  4. The α and δ of the start position. 
  5. Speed normal (▶▶)  or small steps (▶)
See conditions required for solving to fix solve failures.

Tray icons are default off in the latest Win10 version. To set the ASTAP tray icon on, start a solve via the imaging program, go to Windows  "Settings", "Taskbar", "Turn system icons on or off" and set the ASTAP tray icon permanent "on" as shown below:

Usage as a solver with other programs or as PlateSolve2 substitute

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CCDCIEL, using ASTAP as solver.

ASTAP is a menu option in the CCDCIEL program. Just select ASTAP and follow the guidelines in the help file. 

Progress is shown in tray icon and popup notifier.

Solving should be reliable. In case of failure, have a look to conditions required for solving.

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APT: using ASTAP as solver

For APT, Astro Photography Tool use it a PlateSolve2 substitute

  1. Install ASTAP and additional install the G17  star database in the same directory. Typical c:\program files\astap
  2. If you images are more then 3000 pixels wide, start ASTAP. and  click on the ∑  button, select alignment tab and set downsample to 2 (or 3). Save settings by selecting menu FILEe, SAVE SETTINGS, or leave program with menu FILE, EXIT.
  3. Rename the ASTAP.EXE program as Platesolve2.exe  Then select in APT, pointcraft, settings, the directory where this surrogate platesolve2.exe ( renamed astap.exe) is located.

That all. You could now test it with a saved image. To modify the ASTAP default settings, see  astrometric_solving

Optional:

If you want to visualise the images taken in the map of  the HNSKY planetarium do the following:

Start ASTAP manually (PlateSolve2.exe). Click on the ∑  button, select the alignment tab. Check mark "Convert to FITS"  and set "FITS bin" at x4 or x6 r or x8.  Downsample should be set such that the file dimension are near 300 or 400 pixels wide/height for speedy display in the planetarium program.

Note that APT saves the pointcraft image to solve to: .... TemporaryStorage\ImageToSolve.jpg

Set in HNSKY the FITS path to .... TemporaryStorage\ImageToSolve.jpg  (This is the location where APT saves the pointcraft image to solve to)
After solving, either refresh HNSKY with space bar or move to map to the object or open the FITS file in the file menu.

Progress is shown in tray icon and popup notifier.

Solving should be reliable. In case of failure, have a look to conditions required for solving.

Notes:

  1. ASTAP loads the image specified  in the command line. (from APT)
  2. ASTAP solves the image.
  3. The solution is written to the APM file. APT will read it.
  4. If set in the ∑  alignment menu, the JPG is saved as FITS with binning as specified. The FITS file will also contains the solution and could be displayed in a planetarium program. Downsampling should be set such that the file dimension are near 300 or 400 pixels wide/height for speedy display in a planetarium program.
Screenshot APT using ASTAP:

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NINA, Nighttime Imaging ‘N’ Astronomy

For NINA version 1.7, 1.8 and 1.9 nightly #001 use it a PlateSolve2 substitute :

Note that the ASTAP interface in NINA 1.9 nightly #001 doesn't work. You will need 1.9 nightly #002
  1. Install ASTAP and additional the G17 star database in the same directory. Typical c:\program files\astap
  2. If you images are more then 3000 pixels wide, start ASTAP. and  click on the ∑  button, select alignment tab and set downsample to 2 (or 3). Save settings by selecting in the viewer pull down menu FILE, SAVE SETTINGS or leave program with menu FILE, EXIT.
  3. Select in NINA for PlateSolve2 the ASTAP directory and add manually astap.exe in the path as follows:
Alternatively you could rename the ASTAP.EXE program as Platesolve2.exe  Then select in NINA settings, the directory where this surrogate platesolve2.exe ( renamed astap.exe) is located.

To modify the ASTAP default settings, see astrometric_solving

Progress is shown in tray icon and popup notifier.

Later NINA versions could have full ASTAP support making above instructions obsolete.

Solving should be reliable. In case of failure, have a look to conditions required for solving.

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SGP, Sequence Generator Pro:

For SGP use ASTAP as a PlateSolve2 substitute. The orginal PlateSolve2.exe is located at C:\Users\you\AppData\Local\SequenceGenerator\     Where "you" is your user name.

  1. Install ASTAP and additional install the G17 star database in the same directory. Typical c:\program files\astap
  2. If you images are more then 3000 pixels wide, start ASTAP.  and  click on the ∑  button, select alignment tab and set downsample to 2 (or 3) 
  3. Copy or move the astap.exe  and all 290 files with extension .290  to C:\Users\you\AppData\Local\SequenceGenerator\
  4. Rename the original Platesolve2.exe to something like PlateSolve2ORG.exe
  5. Rename ASTAP.exe to PlateSolve2.exe
  6. Test it with SGP. The confidence will be always 999. No PlateSolve2 window will be shown.

Progress is shown in tray icon and popup notifier.

If you select in SGP the PlateSolve2 setting "Max Regions" (=3000) this will force a search up to 90 degrees diameter. However the solver will be most likely stopped halfway by a SGP timeout.

Solving should be reliable. In case of failure, have a look to conditions required for solving.

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Voyager:

For Voyager use ASTAP as a PlateSolve2 substitute. The original PlateSolve2.exe is located at  C:\Program Files (x86)\Voyager 

  1. Install ASTAP and additional install the G17 star database in the same directory. Typical c:\program files\astap
  2. If you images are more then 3000 pixels wide, start ASTAP.  and  click on the ∑  button, select alignment tab and set downsample to 2 (or 3) 
  3. Copy or move the astap.exe  and all 290 files with extension .290  to  C:\Program Files (x86)\Voyager
  4. Rename the original  Platesolve2.exe to something like PlateSolve2ORG.exe
  5. Rename ASTAP.exe to PlateSolve2.exe
  6. Test it with Voyager. E.g. in the OnTheFly section. Confidence will be reported as 999.  E.g. Solved (J2000) => RA 19 59 36,167  DEC 22 42 36,31  PA 277,4 Res. 1,17 [as/px] FL 1131,77 [mm] Star/s 999

Progress is shown in tray icon and popup notifier.

Solving should be reliable. In case of failure, have a look to conditions required for solving.

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Installation of the external Astrometry.net astrometric solver:

MS-Windows:

Install a local copy of Astrometry.net (via ANSVR  or  Astrotortilla)   as the astrometric solver. Or alternatively if you have Win10, 64 bit Creation edition you use the new Linux sub-system


ANSVR: The ANSVR link contains a newer compilation of astrometry.net made for SGP. It runs as a Linux program under Cygwin in MSWindows. Follow up to installation step 9. The link you have to put in ASTAP is as follows:

C:\Users\user_name\AppData\Local\cygwin_ansvr\bin\bash.exe

Adapt "user_name" to the login name used in Windows.

The server program ANSVR is not required. Remove the ANSVR shortcut in the startup menu. Location:

C:\Users\user_name\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup


Alternative Linux sub-system in Win10 64bit Creators edition

Path for the astrometry.net solver program
ANSVR installation:
    C:\Users\user_name\AppData\Local\cygwin_ansvr\bin\bash.exe
Astrotortilla installation:
    C:\cygwin\bin\bash.exe
Win10 subsystem:
    C:\Windows\System32\bash.exe


Linux installation:
The single executable astap could be used anywhere. Standard directory could be c:/opt/astap but also at your home folder.

If you want to use  astrometry.net  this is described at installation. To get the Astrometry.net solver type: sudo apt-get install libcairo2-dev libnetpbm10-dev netpbm libpng-dev libjpeg-dev python-numpy python-pyfits python-dev zlib1g-dev libbz2-dev swig libcfitsio-dev   You also have to download index files.

Path to the astrometry.net solver program "solve-field" could be:

/usr/bin/
or
/usr/local/astrometry/bin


Importing  raw images from digital cameras

This ASTAP version can import raw images from almost any digital camera, For this ASTAP executes the  DCRAW program from Dave Coffin. DCRAW is included with the ASTAP Windows edition and can be installed in Linux by the "sudo apt-get install dcraw" command. 

The file convert option is in the pulldown menu under TOOLS. ASTAP will execute DCRAW with parameters -D -4 and this will produce 16 bit PGM raw files. ASTAP can read these PGM files and convert them to a 16 bit FITS. After conversion the intermediate PGM are no longer required and can be deleted manually. The FITS can be used in the stacking. The Bayer matrix conversion to colour will be applied later in ASTAP. With this method the full depth of the original RAW files will be preserved


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Appendix 1, the stack process:


The stacking process for one shot color color camera's will be mathematically executed as follows:

The master flat is calculated as:

master flat: = (1/n ∑ [flat] - 1/n ∑ [flat darks] )

Where a bias image could be used as flat-dark image. The master flat should be averaged by a 2x2mean to remove Bayer matrix artifacts.

Each image is calculated as:

(image- {∑ [darks]/n} ) / master flat

Then the Bayer matrix is applied and finally the images are stacked in mode average or sigma clipped.

So for average stack:

final image:= 1/n ∑ Bayer(image)

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Send a message if you like this free program. Feel free to distribute !

Succes,  Han  K


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