VTBuilder and BExtractor

Development Notes

• Large Bitmaps under Windows
  • VTBuilder displays elevation layers as very large bitmaps
  • However, you can't just ask for a bitmap of any size from windows
  • It depends not just on memory, but on operating system and graphics card as well
  • According to the Very Large Bitmap Experiment, many older machines cannot produce bitmaps larger than 2000*2000
  • In my experience, using Win32 BITMAP objects works fine on modern machines for bitmaps up to 4096*4096, but will always fail for larger values (e.g. 6000*6800, which is a typical size for a USGS DRG)
  • The Win32 method that fails is CreateCompatibleBitmap()
  • It would be possible to use DIBSections as an alternative to BITMAP objects, and in fact BExtractor does this, but to do so would require making that part of the code Win32-specific, whereas currently all of VTBuilder is platform-independent
• Image Convolution
  • BExtractor currently uses IPL, an discontinued library from a large manufacturer of CPUs, for doing the automatic detection of small building locations
  • IPL was replaced by another library, IPP in 2002, but the new IPP is expensive and restrictive
  • An alternative to IPL might be to use the portable, open-source library ImageMagick, which reportedly does support convolution kernels
  • The legal status of IPL is murky. it is and was freely distributed, yet doesn't explicitly state what occurs in the current situation.  One can speculate from the continued inclusion of most of IPL in OpenCV that its distribution is not objectionable, but nonetheless steps should be taken to port away from it.