posts tagged with cis-cod

• 
  Jul 21, 2024

  Fragmenting the tile data

  When looking at the data segment of CIS/COD images (i.e., the tiles) the byte sequence 0x63 0x6f 0x64 (ASCII: cod) appears several times and thus is conspicuous. According to a wiki page describing a derived video codec it marks the end of a “plane”, a basic building block of wavelet-compressed images. In this post we explore the size distribution of these blocks.

• 
  Jun 27, 2024

  Documenting the file format

  Since the first post on decoding the city database I have learned so much more about the structure of the D-Sat file format: where the image tiles are located, how they are indexed and which information the image header reveals, as well as that the file also contains points describing borders and highways.

• Apr 20, 2024

  Understanding the image header

  One important question remains: Are the tiles in dsatnord.mp stored with or without gaps? To find this out, we would need to know the actual byte size of each tile. But how to find that out? Well, one guess is that the data/file size of each image is stored in its header. The following Python code prints each consecutive 16 bits (two bytes) among the first 20 bytes as unsigned little endian integer:

• 
  Apr 19, 2024

  Viewing tiles with Firefox

  Knowing the offsets of (potential) tiles, we can pick one (56057877) and extract the tile into a file:

• Apr 3, 2024

  Learning about the image format

  The tiles are apparently stored in the lightning strike wavelet-compressed raster image format. Apparently, there exists no free software to work with such files. Here’s what we found:

• 
  Apr 2, 2024

  Finding the tiles

  To find the image tiles in dsatnord.mp and possibly decode them, we had a look at the decompiled lsd26dll.dll. My colleague Jan found the function CLsDecode::GetImageDataSize and figured out that the first lines