An endeavour to reverse-engineer the file format of D-Sat 1.

What is it about?

D-Sat was a series of CD/DVD-ROMs from the 1990s which contained aerial and satellite imagery of Germany.¹ The data was stored in a proprietary file format and thus can only be used with the original Windows programs. Since this is not sustainable, this project seeks to reverse-engineer the file format and develop tools to access the contained data (coordinates, images, etc.).

The first post on decoding the city database is a good starting point for further reading.

Next Steps

• test SK-42 and derivatives (check older usenet discussion on how to decode the geo coordinates)

Files

file name	comment
dsatnord.mp	data for D-Sat 1 CD 1
NPLS32.DLL	NPAPI browser plugin for Netscape/Firefox

Posts

• May 11, 2024

  Visualising Entropy

  Our quest to find the tile index of D-Sat 1 continues. I have described before, what I mean with “tile index” and I have also given a clue that I found something in the first part of the big blob of data dsatnord.mp which I named un1.dat.

• May 6, 2024

  Finding something unexpected

  After having visualised the “uncharted” parts of dsatnord.mp our quest to find the index for the tiles continues.

• Apr 23, 2024

  Searching for the index

  Now let us inspect the unknown segments between tiles where I suspect the index for the tiles. First, we extract all unknown parts:

• Apr 22, 2024

  Getting an overview on the file content

  In the last post we already gained a good overview on the distribution of tiles in dsatnord.mp. Together with the first post this allows us to find the parts of the file which we do not understand, yet.

• Apr 21, 2024

  Visualising the tile size distribution

  With mp.py’s offsets command we can dump tile byte position, size, width and height as follows:

• 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

• Mar 26, 2005

  Decoding the city database

  Note: This post is a copy of the original web page I set up in 2005.

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