Hi all,
I am glad to announce that a new PixInsight module is now available for all Mac OS X users: StarGenerator.
StarGenerator is a tool for generation of
synthetic star fields. It retrieves positional and magnitude data from a large star database and generates a rendition according to a set of user-specified parameters: equatorial coordinates of the center of the field, focal length, pixel size, sensor size, limiting magnitude, and star FWHM. StarGenerator images are strictly linear, but the tool can optionally apply an automatic, nonlinear stretch to facilitate image manipulation and inspection.
ExamplesHere are several examples of pretty synthetic images produced with StarGenerator:
Ursa Major constellation to 11th magnitude:
http://forum-images.pixinsight.com/legacy/SG/UMa.jpgM45 region to 16th magnitude approx.:
http://forum-images.pixinsight.com/legacy/SG/M45.jpgCrux constellation to 12th magnitude:
http://forum-images.pixinsight.com/legacy/SG/Cru.jpgI have also uploaded the corresponding TIFF files:
http://forum-images.pixinsight.com/legacy/SG/UMa.tifhttp://forum-images.pixinsight.com/legacy/SG/M45.tifhttp://forum-images.pixinsight.com/legacy/SG/Cru.tifStarGenerator produces 32-bit integer images. This is because a large dynamic range is necessary to render faint stars linearly. For example, approximately 10
9 discrete pixel values are required to render a 16th magnitude star in a linear space spanning to magnitude -1.5 (Sirius). Note that this largely exceeds the range of 32-bit floating point.
PurposeThe main purpose of this tool is to generate synthetic reference images for mosaic construction. With these reference images, one can build complex mosaics of any practical size, with the help of the DynamicAlignment and StarAlignment image registration tools in PixInsight.
I have written StarGenerator specifically for mosaic construction with the four detectors of the
LAICA CCD array used at the prime focus of the
3.5-meter telescope of
Calar Alto Observatory, in southern Spain. With this instrument, LAICA can produce 256-megapixel mosaics covering one square degree. Due to the extremely small superposition between LAICA frames, and also to the large-field distortion of the 3.5-meter telescope, these mosaics cannot be built accurately by registering the images. The only practical way to build them is by adapting the four frames to a reference image with a sufficient number of stars, using DynamicAlignment (StarAlignment cannot be used in this case, due to strong field distortion).
Star DataThis initial version of StarGenerator uses the PPMX astrometric catalog. This catalog includes 18,088,919 stars and is complete up to magnitude 12.8. All the information and original source data is available at the CDS:
http://cdsarc.u-strasbg.fr/cgi-bin/Cat?I/312Projection SystemsStarGenerator uses three projection systems:
-
Polar Stereographic projection for high declinations.
-
Lambert Conformal Conic projection for intermediate declinations.
-
Mercator Cylindrical projection for nearly equatorial declinations.
The projection system is selected automatically as a function of the coordinates of the center of the field. Note that the three projections are conformal, i.e. they preserve angles. In general, if you generate a wide field rendition of the sky (say above 15 or 20 degrees of FOV, for example), don't expect StarAlignment to work properly due to strong distortions, which are inherent to any system that projects large portions of a sphere on the plane.
Positional accuracy of StarGenerator renditions is only limited by the accuracy of star database positions (0.01 arcseconds) and by geometric resolution, which depends on the size of the generated image and the dimensions of the field of view, i.e. on focal length and pixel size parameters.
AvailabilityFor now the StarGenerator module is only available for Mac OS X,
but I hope that, since I have made the entire source code publicly available (under GPLv3 license, see below), it will be compiled on Linux and Windows very soon. Anyway, of course StarGenerator will be available for all supported PixInsight platforms in September.
Source CodeStarGenerator has been released under an open-source license: GPL version 3. This means that the entire source code of this module is publicly available, and it can be used under the terms of the GPL v3:
http://pixinsight.com/export/StarGenerator/StarGenerator-osx-src-1.0.0.38-20090818.zipFor now the code is largely undocumented, but this will change soon. Please feel free to contribute and participate in the development of this tool. A first contribution could be compiling the module for Windows and Linux. This should be very easy for active PixInsight developers
Short-Term ImprovementsThis is a brief to-do list, sorted by priority:
- Parallelization of the star generation routine, to use all available processor cores.
- Use of a denser star catalog. USNO A2 is a firm candidate.
- Implementation of additional projection systems, for example area-preserving projections.
InstallationTo install StarGenerator you have to download two files: the star database (generated from PPMX data), and the module binary file. The star database is necessarily a pretty large file: 242 MB. Download it to any folder under your home folder on your Mac (for example, to your Downloads folder):
http://pixinsight.com/export/StarGenerator/PPMX.binThen download the module binary file:
http://pixinsight.com/export/StarGenerator/StarGenerator-osx-x86-1.0.0.38-20090818.zipTo install this file, please follow these steps:
1. Exit PixInsight, if you have it running.
2. Double-click the zip archive to uncompress it. You'll get the module file:
StarGenerator-pxm.dylib
3. Right-click the PixInsight.app application. It is on the /Applications folder if you copied it to that folder, as usual.
4. From the context menu, select Show Package Contents.
5. Now a Finder window opens for the PixInsight.app folder. Expand the Contents/MacOS/bin folder.
6. Copy the module file (step 2) to PixInsight.app/Contents/MacOS/bin
7. Run PixInsight.
8. From the main menu, select Process > Modules > Install Modules.
9. On the Install Modules dialog, click the Search button. A new module should be found, which should be the StarGenerator-pxm.dylib file that you copied in step 6. Now click the Install button and you are done.
Yep, I know I must implement a better/easier way to install modules on the Mac. It is in the to-do list, indeed
Enjoy!
