The Joseph R. Lynch Observatory at Drexel University

Our prefered image analysis tools

After a long search, I have found a collection of programs for displaying, aligning, stacking and analyzing ccd images. This search came about because the primary option for image analysis on Linux was IRAF. For an opinion about IRAF which is similar to mine, see Justin Pryzby's IRAF rant. He is developing his own set of tools, which we have just started using for the initial calibration.

The packages that we use (thanks in advance to their respective authors) include libastro for bias, dark and flat calibration, SAO ds9 for image display, SExtractor for star finding, WCS tools for coordinate fitting and simple manipulations, and SWarp for stacking the resulting images. That these are not one single package (such as CCDsoft or Maxim for Windows or IRAF) does nothing to reduce their applicability and power. I have written a short shell script which puts most of the steps together and can be applied to a succession of images.

The usual analysis pipeline looks something like this:

  1. Combine the bias, dark and flat frames and calibrate the data from them with calib_main
  2. Download DSS image of sky region within ds9
  3. Rotate/flip all images to match DSS image using imrot
  4. Make a guess at the coordinates of one image point using the DSS image
  5. Extract star list from DSS image with SExtractor
  6. Generate star-table from extracted list with imstar
  7. Extract star list for each separate image
  8. Apply coordinate system to each image based on matches between DSS stars and the extracted list, using imwcs
  9. Stack resulting images using SWarp
  10. View result, and make measurements within ds9

The shell script that I mentioned previously performs steps 3 and 5-8. Step 3 may or may not be necessary, but I've included it for completeness. Step 4 is currently necessary for us because we don't have the telescope talking to the computer yet, so we need a guess at the coordinates of the images.

How do I use these tools? I'm on Windows!

ds9 is available for a wide variety of operating systems. Check their website for more information. For the other tools, you might try Cygwin, but you will have to recompile the applications, and I don't know how well they will work. If you have success using these programs under Cygwin, let me know! I suspect it is not an environment supported by the developers of the above software, so please don't tell them I suggested it.

Another option is to try out the Ubuntu live-CD. Just follow the download link, pick a mirror near you and select the appropriate CD for your computer. Ubuntu is very easy to use, and the live CD gives you a chance to play around with Linux, with out installing anything to your harddrive. It does not come with the above software, but you can download and try it out while in the live-CD session. If you like it, you can install Ubuntu from the live-CD!


The Joseph R. Lynch Observatory has been made possible by the Generosity of Joseph R. Lynch '58 and the GE Foundation.

Page maintained by Gordon Richards

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