Galaxies3D Bitmaps and Bitmap Parameter Files
Galaxies3D can "paint" the scaled patch of a bitmap image across the base grid of a view or scene:
The Header Section of the Galaxies3D datafile has a place for the name (without the 'txt' extension) of a plain text bitmap parameter file that gives Galaxies3D the information it needs to do such painting. The referenced plain text bitmap parameter file resides in the same folder as the main program. For example, here is the Header Section for the Galaxies3D Datafile for "Globular Clusters Within 25 Kly of Galactic Center"; the name of the plain text bitmap parameter file is "Milky Way1 4xr.txt":
################################################## 00000000011111111112222222222333333333344444444444 12345678901234567890123456789012345678901234567890 ################################################## Title Globular Clusters Within 25 kly of Galactic Center Input Distance Units: kpc Input Coordinate System Equatorial Output Coordinate Plane Galactic Output Distance Units kly Default Color Blue Default Sphere Size (-5..5) -2 Default Line Width (-5..5) -3 Default Label Size (-5..5) -4 Show Lines false Show Labels false Show z=0 grid Default Camera Zoom (-120 to -10) -62 Grid Z Position (-50 to 50) 16 Bitmap Milky Way1 4xr Comment: from Harris 2010 revision #################################################
This bitmap data item "Milky Way1 4xr" (in the above example) in the Header Section is the name of a plain text file (without its ".txt" extension) that gives Galaxies3D:
The bitmap image used (typically a JPEG image) must meet the following requirements:
This is the structure (by example, the bitmap parameter file for the bitmap "Milky Way1 4xr.jpg") for the plain text bitmap parameter file:
################################################## 00000000011111111112222222222333333333344444444444 12345678901234567890123456789012345678901234567890 ################################################## Bitmap File Name Milky Way1 4xr.jpg Distance Units ly Coordinate Plane Galactic Bitmap Size (pixels) 4200 Bitmap Scale (eg ly/pixel) 32.39736 Pixels Sun to TOP 2905 Pixels Sun to LEFT 2100 Comment: Milky Way Galaxy Annotated, by Robert Hurt, NASA/JPL-Caltech #################################################
Notes on the structure of the bitmap parameter file:
As in Galaxies3D datafiles, the actual data read by Galaxies3D in the plain text bitmap parameter files begins in the 30th column. The text before the 30th column are prompts to remind a person editing the datafile what data should go where; Galaxies3D ignores this prompting text.
Bitmap File Name: the name of the actual bitmap image file.
Distance Units. Acceptable options are: AU, ly, kly, Mly, Gly, pc, kpc, Mpc, Gpc.
Coordinate Plane: the coordinate plane of the image. Acceptable options are: Equatorial, Galactic and Supergalactic.
Bitmap Size (pixels). Must be an integer: the number of the pixel width or height of the bitmap (bitmap must be a square, width = height).
Bitmap scale. A real number = the scale of the image = the number of distance units (as listed in Distance Units) per pixel.
Pixels Sun to TOP. Must be an integer. The number of pixels between the Sun or Earth in the image and the TOP of the image.
Pixels Sun to LEFT. Must be an integer. The number of pixels between Sun or Earth in the image and the LEFT side of the image.
Comment: ignored by the program.
The absolute area covered by the bitmap image (in light years x light years, for example) should be comparable to the absolute area covered by displayed dataset. If the bitmap image is larger in absolute area than the absolute area of the displayed base grid, Galaxies3D will crop the bitmap to fit the absolute grid area. If the bitmap image is smaller than the absolute area of the displayed base grid, than Galaxies3D actually tries to add margin to the bitmap until it fits the absolute grid area. If you give Galaxies3D a bitmap of an area 100 kly x 100 kly and ask it to use the bitmap to paint a grid 100 Gly x 100 Gly, you will be asking the program to expand the bitmap to astronomical (literally!) proportions, and Galaxies3D will instead complain or crash.
