Plate-solving software




Дата канвертавання24.04.2016
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PLATE-SOLVING SOFTWARE
Astrometry.net, http://nova.astrometry.net, 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


http://nova.astrometry.net/user_images/15598#annotated
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, astrometry.net and AstroTortilla are NOT developed by the same group.
AstroTortilla (AT) is essentially a graphical user interface to the local version of nova.astrometry.net.  Although you do not have to execute any of the ‘programmer’ commands, I found it helpful to read the astrometry.net help file.

http://astrometry.net/doc/readme.html

In fact, when you install AT, are installing the local version of astrometry.net, which is run through Cygwin.  Astrometry.net is a Linux-based system.  Cygwin is a way to run Linux packages, like astrometry.net, 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.


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 .5want 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. If you need more index files later, these can be downloaded without doing a full 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

http://www.newastro.com/book_new/camera_app.php
Once you know the FOV for your equipment, download the latest version of AstroTortilla
http://sourceforge.net/projects/astrotortilla/files/
It is a Windows executable file. I’ve installed this on three PCs (2 with XP and 1 with Windows 7) and it went without issue on all. Windows 8 may be a different story.
The following screenshots are for Windows XP. Windows 7 is not that different and the following should work for both.
Double click the downloaded file, which will have a name like

AstroTortilla-0.5.2.0-fixed-x86.exe


If you get a security warning, click Run



Select a language and Click OK.



Click Next


If you want, read the Agreement. Then select “I accept the agreement” and click Next. The Agreement is innocuous.


Unless you know what you are doing, use the default Destination Location, and click Next


Leave all three boxes checked and click Next


For XP -- Unless you know what you are doing, use the default Cygwin Location and click Next.


For Windows 7 -- Because Windows 7 will NOT let you easily install anything to the root directory, you have to find another location. I installed cygwin to Documents/My Documents. Use the Browse button, then Click Next.

Here is the first place where you need to make some decisions.


Use the international server.

Leave the Tycho2 indexes unchecked

Select the narrowest and widest index files, based on the values that you wrote down earlier.
Click Next

Click Next


 

Select the options that you like. I use the defaults. For the first time, you must check “Create Cygwin setup menu entry.” Click Next


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


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.


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.



 

Click Next


Check “Install from Local Directory” and click Next


Win XP – Assuming that you did NOT changed the location of Cygwin earlier, use the default and Click Next.


Win 7 – Type the location that you used in the Cygwin Location box earlier. Click Next.

Use the default and click Next.




Click OK. Click Next


Click Next


Use defaults and Click Next




Cygwin Setup will work a while, but much less time than AT install.  

When completed, Click Next. This may happen automatically. If so, see next window.

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 (Start -> Programs -> AstroTortilla -> AstroTortilla)


2.  Make sure that the Telescope section shows Disconnected.  We want to 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

5.  Click Capture and Solve.  Navigate to the installed example images

For Windows XP


C:\cygwin\usr\share\astrometry\examples

For Windows 7 (Note this will vary with where you decided to install Cygwin earlier. If you chose My Documents, then look in

C:\Users\userid\Documents\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.




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.

 
Once you get AT to solve apod4.jpg, look in the My Documents 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 (not much use looking at these) and images (*.png).



 

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.



 

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.  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)



 


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.


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.sf.net\AstroTortilla
In Windows 7 onwards, it’s in
C:\Users\userid\AppData\Local\astrotortilla.sf.net\AstroTortilla
For more info on using the configuration file,

see https://sourceforge.net/p/astrotortilla/home/Configuration/


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 example



[AstroTortilla]

work_directory = C:\Users\userid\Documents\AstroTortilla\


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