StarSplatter Tests 2 - Constellations

Frank Summers
Space Telescope Science Institute

Constellation Tests

Tests 1 focused only on the constellation of Orion and got good results. This second set of tests tries many other constellations to hone the procedure, parameters, and code.

The Data Set

The base data is the same as for Tests 1, however, for some unknown reason, the filenames are different. I use a representation of the night sky found in the Yale Bright Star Catalog (YBSC).  The position of each star in YBSC has been transformed to 3D using parallax information found in YBSC or in the Hipparcos catalog.  For the visualization, other information about the intrinsic brightness of the stars is needed.

Refining the Tcl Scripts

In Tests 1, I created a couple utility Tcl scripts for calculating the size and brightness of a star splat.  Here, we can use many different starfields to explore the best parameter settings that work on a range of starfields at the same time.
 
  • First, I excised the two Tcl scripts into files separate from the main viz routine. One needs to use a line like
    • set auto_path [linsert $auto_path 0 /home/summers/viz/starsplatter/lib]
    to search a library of routines for unresolved procedure calls.
     
  • The procedure that needed refining is "calc_den_and_sl.tcl" and it was the subject of many tests.  The most telling of all is a test that creates stars of increasing magnitudes. A sequence of stars is created with adjacent ones differing by one magnitude. Various rows are created with the stars at different distances in each row, but same apparent magnitude. Hence, we check how magnitudes compare against each other, and ensure that it is independent of distance.
  • The script for the test, mag_test.tcl
  • The results of the test, after tweaking, mag_test.jpg (23 kb)
  • The resulting Tcl scripts.  These were optimized for a high contrast starfield -- the brightest stars jump out more than they do in reality.  This simulates the view that most people, living in light polluted urban or suburban areas have. I would optimize the parameters a little differently if I were trying to purely simulate reality.
  • get_pixel_scale.tcl
  • calc_den_and_sl.tcl

    • The Constellations

    Each image is 1000 x 1000 pixels.  Most of them are available in reversed format (black stars on a white background) as well. In fact, one of the possible uses of these files would have been done in reversed format, so they may look better reversed than in standard white on black.

    Last modified: November 4, 1999  --  Frank Summers summers@stsci.edu