AT is essentially a graphical user interface to astrometry
PLATE-SOLVING SOFTWARE
, , is a Web-based blind plate-solver. You submit an image online and it cranks away and tells you
1. RA and Dec
2. FOV
3. Catalogued, interesting objects in the FOV
4. Skycharts at various scales
While you can speed up the process by telling providing rough info on location, FOV, etc, THAT'S NOT REQUIRED. It will find the location with nothing more than the image 90+% of the time. It actually works best with fewer stars and an un-processed image.
The algorithm relies on star pattern identification. Therefore, the actual object of interest does not even have to show up in the image. I often use ISO 6400 to 12800 and 5-10 seconds.
Here's a link to one of M95 that I submitted last year when looking for SN 2012aw
This is not the best example, since M95 is fairly bright.
I had been using this somewhat for a couple years. However, it does require manual adjustment of the mount to center an object. Therefore, I have switched to AstroTortilla.
Note that, while interlinked, and AstroTortilla are NOT developed by the same group.
AstroTortilla (AT) is essentially a graphical user interface to the local version of nova.. Although you do not have to execute any of the ‘programmer’ commands, I found it helpful to read the help file.
In fact, when you install AT, you are installing the local version of , which is run through Cygwin. is a Linux-based system. Cygwin is a way to run Linux packages like , from a Windows machine. (Layers on layers, it seems). All the ‘geeky’ stuff described in the Readme file is done automatically by AstroTortilla.
During the install, you need to decide what index files you download. The full index files are about 10 GB. You typically will not need the entire set. To determine the optimum set, you'll need to have a good idea what the field of view dimensions are for YOUR scope / camera.
The following is not mine, but is copied from the above Readme page. Thanks to the astrometry team for all their work!!
Each index file is designed to solve images within a narrow range of scales (angular size). The index files designed to solve small images are rather large files, so you probably only want to grab the index files required for the images you wish to solve. If you grab extra index files, the solver will run more slowly, but the results should be the same.
The files are named index-42XX.fits or index-42XX-YY.fits. These are called the “4200-series” index files and are the default install. If you want to know more about the index files, see the link to the Readme file above.
Each index file contains a large number of “skymarks” (landmarks for the sky) that allow our solver to identify your images. The skymarks contained in each index file have sizes (diameters) within a narrow range. You probably want to download index files whose ranges are, say, 10% to 100% of the sizes of the images you want to solve. As mentioned, the size of the image is determined by the telescope and camera you used for the image.
For example, let’s say you have images that are 55’ x 80’. You should grab index files that contain skymarks of size 5 to 80 arcminutes. Referring to the table below, you should grab index files 4203 through 4210.
Once you have determined the index files you want, write down the smallest and the largest file name. They will be downloaded during the install.
|Index Filename |Range of skymark diameters |
| |(arcminutes) |
|index-4219 |1400 – 2000 |
|index-4218 |1000 – 1400 |
|index-4217 |680 – 1000 |
|index-4216 |480 – 680 |
|index-4215 |340 – 480 |
|index-4214 |240 – 340 |
|index-4213 |170 – 240 |
|index-4212 |120 – 170 |
|index-4211 |85 – 120 |
|index-4210 |60 – 85 |
|index-4209 |42 – 60 |
|index-4208 |30 – 42 |
|index-4207-* |22 – 30 |
|index-4206-* |16 – 22 |
|index-4205-* |11 – 16 |
|index-4204-* |8 – 11 |
|index-4203-* |5.6 - 8.0 |
|index-4202-* |4.0 - 5.6 |
|index-4201-* |2.8 - 4.0 |
|index-4200-* |2.0 - 2.8 |
If you don’t already know the FOV for your scope and camera(s), download and install Ron Wodaski's CCDCalc, which is a great tool for this and is free.
Download at
Once you know the FOV for your equipment, download the latest version of AstroTortilla.
It is a Windows executable file. I’ve installed this on five PCs (2 with XP, 1 with Windows 7, and 2 with Windows 8.1) and it went without issue on all.
The following screenshots are for Windows XP. Windows 7 and 8.1 are not that different and the following should work for both.
Double click the downloaded file, which will have a name like
AstroTortilla-0.x.x.x-x86.exe
If you get a security warning, click Run
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Select a language and Click OK.
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Click Next
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If you want, read the Agreement. Then select “I accept the agreement” and click Next. The Agreement is innocuous.
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Unless you know what you are doing, use the default Destination Location, and click Next
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Leave all three boxes checked and click Next
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Unless you know what you are doing, use the default Cygwin Location and click Next.
I am not positive, but I think that cygwin MUST be installed in a root directory; although not necessarily the C: drive root directory. Note that for a Windows 7 PC, I installed cygwin to the root directory of a separate SSD. Use the Browse button, then select the desired drive. Click Next.
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Here is the first place where you need to make some decisions.
Use the international server, unless you are in Finland.
Leave the Tycho2 indexes unchecked, unless you have VERY wide FOV images to solve.
Select the narrowest and widest index files, based on the values that you wrote down earlier.
Click Next
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Click Next
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Select the options that you like. I use the defaults. For the first time, you must check “Create Cygwin setup menu entry.” Click Next
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This is one last chance to check all the options of the last few screens. When you are sure that you have what you want, Click Install
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This install will take some time (typically, tens of minutes), consisting mostly of the index files download.
Note that during the download, the actual download volume will likely exceed the target size, because of an anomaly in the display. This is nothing with which to be concerned.
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Uncheck both View README.txt and the Launch AstroTortilla. Click Finish.
Once you have completed the download and the new install, we need to complete the initialization of Cygwin.
Start -> Programs -> AstroTortilla -> Cygwin Setup.
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Click Next
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Check “Install from Local Directory” and click Next
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Assuming that you did NOT changed the location of Cygwin earlier, use the default. If you installed cygwin in the root of a separate hard drive, browse to that drive.
Click Next.
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Use the default and click Next.
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Click OK. Click Next
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Click Next
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Use defaults and Click Next
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Cygwin Setup will work a while, but much less time than the AT install.
When completed, Click Next. This may happen automatically. If so, see next window.
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Check the Add icon to Start menu and Click Finish
One thing that makes a big difference is the index image files that AT uses. The best ones, in my experience, are the 4200 files. They are the default install; so I will assume that you have the 4200 index files from here on. The 4200 index files are based on the 2MASS catalog.
Now we can see if everything went well
1. Open AT (For Windows XP and 7 - Start -> Programs -> AstroTortilla -> AstroTortilla). For Windows 8, it will depend upon how you have set up the Start Menu (Metro or something else). I just pinned AT to the Taskbar on the Desktop
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2. Make sure that the Telescope section shows Disconnected. We want to evaluate the install in small steps to ensure everything is working OK.
3. Set Camera to File Open Dialog
4. Set the Solver parameters as follows.
Scale minimum 20
Scale maximum 40
Scale refinement 0.1
Search radius 45
Custom Options to --downsample 2 –overwrite
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5. Click Capture and Solve. Navigate to the installed example images
For Windows XP
C:\cygwin\usr\share\astrometry\examples
For Windows 7 and 8 (Note this will vary with where you decided to install Cygwin earlier. If you chose the C: drive, then
C:\cygwin\usr\share\astrometry\examples
Select apod4.jpg, click Open
Watch the text at the bottom of the AT window.
It should start "Solving"
It should find 435 sources. These are the number of stars that AT identified in the apod4.jpg image
It will then try to match those sources with the index files. It will list a lot of index files that did NOT work.
Eventually, it should find a match and show the amount of time it took to solve. This will vary with your PC. In my case, it was 18 seconds.
The "Previous solution' data in the AT window will show the location of the apod4 image.
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It should be close to:
RA 12h29m
Dec 56 36'
Field size 32.76 x 23.40
If this doesn't happen, then something occurred during the install.
I may be doing something wrong, but I am not able to get the annotated plots saved, UNLESS I setup the working directory in the configuration file.
Where's the configuration file?
The configuration file for AstroTortilla is in the local settings directory
In Windows XP, it's in
C:\Documents and Settings\userid\Local Settings\Application Data\astrotortilla.\AstroTortilla
In Windows 7 and 8.1, it’s in
C:\Users\userid\AppData\Local\astrotortilla.\AstroTortilla
For more info on using the configuration file,
see
To define where the output files go, set the work_directory. I use a new sub-folder called AstroTortilla.
Windows XP example
[AstroTortilla]
work_directory = C:\Documents and Settings\userid\My Documents\AstroTortilla
Windows 7 and 8.1 example
[AstroTortilla]
work_directory = C:\Users\userid\Documents\AstroTortilla\
Once you get AT to solve apod4.jpg, look in the working_directory folder. There will be a folder there starting with a number (“0”). There should be new files there, all starting with apod4.
Every time you run AT, another sequentially numbered folder will be added. Look in the most recent folder. If you close AT and re-start, it will re-start at the “0” folder.
The new files are a mix of text and images (*.png). The text files contain extensive details. I don't use these much.
apod4-objs.png shows the stars, circled in red, that were identified in the first pass
apod4-indx.png shows the stars and lines used to solve the exact location
apod4-ngc.png shows the final solution.
When it can, AT will annotate the ngc.png image with objects
The Astrometry Readme link from before provides more info on these files, if you are interested. Note that the page lists the apod files as being in a Demo folder. That's an old version and hasn't been corrected yet. It's now Examples.
Once you get apod4 to solve, try my image of M86a, sent with this document. (250 KB). Note this image is 77’ x 51’. If you did not download at least index files 4208 to 4210, then you won’t be able to test M86a. See the separate tutorial and adding index files.
Set Solver parameters
Scale minimum 1
Scale maximum 2
The others can be left where they were before, i.e. --downsample 2 --overwrite. In fact, you may never change them again.
These should REPLACE the default parameters. The default parameters turn off the generation of *.png graphic files, which I find useful to review. I do add --no-plots at times to speed up solving, when I am not interested in the plots.
At some point, you may need to learn the other parameters in order to solve a particular image, but, for now, go with just
--downsample 2 --overwrite
Click Capture and Solve. Navigate to wherever you stored M86a, select M86a, and click Open.
AT should find 981 objects.
My PC took 35 seconds and annotated 10 NGC objects (M86-ngc.png)
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After success there, try one of your images.
Recall the FOV values that you used to download index files. This is what you use to set Scale Min and Scale Max in AT.
The Scale Minimum in AT should be less than the smaller of the two FOV dimensions. I'd suggest half.
The Scale Maximum should be greater than the larger of the two FOV dimensions. I'd suggest 2x.
Be sure to match units, typically degrees.
My experience is that once you get the AT parameters set for a given telescope and camera combination, then using AT becomes very easy. It's the parameters that are the bump in the road.
P.S.
As far as your images, here some tips.
You don't need a high quality image, just one with a fair number of stars. I often use the maximum ISO for my camera and short exposure.
You don't need to stack or post-process images for AT. A single image is fine.
You can control the location of the output files using the AT config file (astrotortilla.cfg), along with a lot of other stuff.
REVISION LOG
REVISION 2 (April 23, 2014)
Geof Lewis adds
1. Under Windows 7 the config file is in saved in a hidden folder, so Windows 7 users, who have not already done so, will need to navigate to hidden files and folders and select and save the 'show hidden files and folders' radio button to be able to see and edit this file.
2. A further feature that I like since I use more than one imaging configuration is the ability to save/load different named version of the configuration file for different telescope FOV, e.g. I have a Meade 10" which I sometime use native and sometime with an attached FR/FF. I also image with a Williams Optics ZS again with and without FF/RR so in total that is 4 different FOV settings. By saving configuration files for each I can just 'Load' which ever file I need acccording to my imagaging configuration for any particular session and be confident that I have the correct Scale Min and Scale Max parameters set for my current session
TIPS from other users
If possible, use units of arcsecperpix aand set the scale low and scale high very close together. This will speed up solves substantially. (astroman2)
Unless you really want the annotate plots, set --noplots. This will also speed up solves. (astroman2)
REVISION 3 (May 5, 2014)
Acknowledged use of Help file
Added Windows 8.1 install and use
Changed install directory directions
Added need for working directory in config file in order to save annotated plots
Added a sentence noting that --no-plots will lower solve times. (Thanks to astroman2.)
Fixed a few typos.
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