Hidden threshold in the map generator?

[Corbeau-1]

When I set temperature = 0, amount of hills/mountains = 0 and wetness =100, I am still getting a number of hills and deserts.

When I set wetness = 0, I still get forests. See image. (No deserts and hills in the image because I removed them from the ruleset.)

I have a feeling there is a hidden threshold. If not, I'm looking for a way to exactly control the amount of some types of terrain, going from zero to all.

I tried playing with property-wet and property-mountainous, setting them to 0 or 100, but it didn't work.

Generators I used were Pseudo random height and Fractal height.

[lmoureaux]

I don't see a hidden threshold for mountains. For forest, you can't go below 5%. You may be interested in the algorithm description if you want to achieve specific results.

[Corbeau-1]

Thanks, I'm checking it out.

So, the 5% for the forests is the threshold. However, I'm seeing more forest than expected:

Here it's 32 tiles where I'd expect 10.

[Corbeau-1]

Ok, I checked the code. Code for percentage of forests is an absolute mess. I've seen messes in my life, but this one literally outmesses them all. I am not exaggerating. I will append a summary.

As for mountains, right, it's this:
mountain_pct = mount_factor * wld.map.server.steepness * 90;

Indeed, as you say, if steepness is set to zero, there should be no mountains on the map. Any idea why they are there?

Theoretically, the fact that I removed all other terrain types except mountains and forests could mess things up. But I don't see how.

And the mess with forest_pct:

#define MAP_INDEX_SIZE (wld.map.xsize * wld.map.ysize)

sqsize = sqrt(MAP_INDEX_SIZE / 1000);

#define MAX_COLATITUDE 1000

#define COLD_LEVEL
  (MAX(0, MAX_COLATITUDE * (60 * 7 - wld.map.server.temperature * 6) / 700))

ice_base_colatitude = 
(MAX(0, 100 * COLD_LEVEL / 3 - 1 * MAX_COLATITUDE) + 1 * MAX_COLATITUDE * sqsize) / (100 * sqsize);

#define ICE_BASE_LEVEL ice_base_colatitude

int polar =
2 * ICE_BASE_LEVEL * wld.map.server.landpercent / MAX_COLATITUDE;

factor = (100.0 - polar - wld.map.server.steepness * 0.8) / 10000;

forest_pct = factor * (wld.map.server.wetness * 40 + 700);

[lmoureaux]

I think you're seeing the effect of terrain assignment in the gaps between the normal mountains. This proceeds according to Table 11 (also see the text above). I'm afraid there is no way to produce an all-grass map with this algorithm (a single terrain can always be in the required or preferred set and never in the avoided set).

This being said, you could change the forest terrain to make it identical to grassland.

[Corbeau-1]

Well, I could always simply remove it from the ruleset altogether. But I'd like to have one or two different types of terrain that appear as rare patches here and there, but then again, it's not that crucial. If it's that difficult to do, I'll think of something else. Thanks.

[XHawk87]

If you want to tweak how the map generation worked, it's relatively straightforward to do so in lua. For example:

function customise_map()
  for tile in whole_map_iterate() do
    if tile.terrain:rule_name() == "Mountains" then
      tile.change_terrain("Grassland")
    end
  end
end

signal.connect("map_generated", "customise_map")

This will replace all mountains on the map with grassland.

[Corbeau-1]

Again, I can remove all mountains by removing "Mountains" from the ruleset. I want to retain some.

[XHawk87]

If you want to randomly retain some, you could use something like this: https://github.com/longturn/Sim/blob/266b88ce6f822745fabe10d754586accfd97b3a7/Sim06/script.lua#L124