FS2004 Slartibarfast and color values of the bitmaps


I'm reading the Scott Gridley's tutorial: Freeflow about Slartibarfast, but I'm having this problem generating the .bgs files.

I have to say I'm not using the program Terrascene, as he does in the tutorial. Instead, I'm exporting directly the vector data from OpenStreeMaps into bitmaps following his indications about the color of the watermasks. In the tutorial he metions:

Click the RGB tab on the color window, and enter 120 into each of the three channels. This makes the background a nice gray color that Slarti will interpret as land.

“Water – Ocean Bays and Estuaries” –we’ll want to see those in our images. Click on the “Color only” radio button, then click the color box to select a custom color. Enter “6” into each of the three channels.
As far I've understood, these are RGB values (120 for ground and 6 for black water). So, using Gimp, I've assigned these values to the bmps that I've obtained from the vector of OSM.

The problem is, when I execute slartibarfast, after the program processs my .bmps, this happens:

4 (2x2) cells to be processed.
--> Loading water data
Scaling "D:\fsdev\Kodiak\Slarti\input\LOD08_1.bmp"
Promoting image type 1 to 16-bit - done.

Scaling "D:\fsdev\Kodiak\Slarti\input\LOD08_2.bmp"
Promoting image type 1 to 16-bit - done.

Scaling "D:\fsdev\Kodiak\Slarti\input\LOD08_3.bmp"
Promoting image type 1 to 16-bit - done.

Scaling "D:\fsdev\Kodiak\Slarti\input\LOD08_4.bmp"
Promoting image type 1 to 16-bit - done.

The watermask only has a single value - ignoring it completely!
*** Problem preparing watermap - erasing it.
I've been searching more information about how the watermask bmp have to be set on the Scott tutorial and in the Slarti manual too. I've searching in the old post in AVSim forums (it's very difficult because they have merged the old Scenery Design Forum with the FSX forum!) but I didn't find information about this problem.

Any of the veterans do remember any info about this kind of problem?

As usual, thank you for your time.

Best regards and please, stay safe.


Staff member
Resource contributor
Slartibartfast example:


Extract to desktop, open the folder, double-click BGS_2107.bat

Note that the source image is slightly bigger than the desired output. That eliminates edge discrepancies. The INF trims the output.
The produced 2107.bat will produce the actual BGLs when double-clicked.
Hi Dick

After check your files I've seen that the sea must be a total black. It's not necesary adjust its RGB value up to 6, like in the tutorial said. For the ground, a plain gray (RGB 50%) works correctly.

My mistake was to assign a RGB low value to the sea. For that reason, Slarti only dectected one value and it didn't find the difference between ground and sea.

Now works correctly.

Thank you very much Dick.