[Freeciv-Dev] Re: (PR#7584) [RFC]: generalizing terrain in mapgen

["Marcelo Burda" <mburda@xxxxxxxxx>]

<URL: http://rt.freeciv.org/Ticket/Display.html?id=7584 >

Le jeu 02/09/2004 à 02:09, Jason Short a écrit :
> <URL: http://rt.freeciv.org/Ticket/Display.html?id=7584 >
> 
> We don't really have a plan yet.  But we have the beginnings of a plan.
> 
> I speak below in terms of percentages.  Each percentage can be
> represented as an integer from [0,100] or as a floating value [0,1] or
> as a larger integer [0,1000000].  It doesn't really matter.
> 
> The terrain server options are removed.  In their place go:
> 
>   landmass : this keeps the same meaning
>   wetness : ranges 0 to 100%
>   steepness : ranges 0 to 100%
>   temperature : ranges 0 to 100%
> 
> the question is how to use the last three values.
> 
> (Side note: The current model is that the "steep" terrains are just the
> highest ones.  While this may not be accurate it, keeping it can't make
> things any worse than they are now.)
> 
> We already have a height map.  This assigns a height to each terrain
> from 0 to 100%.  We also know temperature, which we can access directly
> or make a temperature map out of (from 0 to 100%).  We can also make a
> wetness map *after* water is placed.  Wetness is affected by height,
> presence of water, and temperature.
> 
> -----
> 
> So we need some way to match terrains up with these values.  Marcelo's
> already made a patch that does something along these lines.  But here is
> my idea.
> 
> For each terrain, we give a range of values:
> 
>   [terrain_grassland]
>   height_min = 0
>   height_max = 50
>   wetness_min = 30
>   wetness_max = 80
>   temperature_min = 30
>   temperature_max = 80
>   likelihood = 10
> 
> Note these are percentage values (except the last one which is just a
> ratio).
> 
> For each tile, we look at it's height, wetness, and temperature and
> consider each possible terrain.  We find the terrain that matches most
> closely.  Something like:
> 
>   - If there is a single terrain whose values it falls within, choose
> that terrain.
>   - If there is more than one terrain, choose one at random based on the
> likelihood.
>   - If there is no matching terrain, choose the closest one.
> 
> Another way this could be done is by assigning an "average" and a
> standard deviation for each value:
> 
>   height = 25
>   height_dev = 15
> 
> then find the probability that matches the tile.  With a normal
> distribution if the height of the tile is 40 that's one standard
> deviation off so the chance is 60% or something.  We then multiply
> together the probability based on each dimension of matching (height,
> wetness, temperature) and multiply the whole thing by the probability of
> the terrain.  We do this for each terrain and pick one at random based
> on the resulting numbers.
> 
> landmass should act as a dividing point.  Ocean terrains are completely
> separate from land terrains.  The coastline should be placed at
> height=0.  So we end up with heights actually ranging from -100% to
> 100%.  Thus ocean terrains work exactly the same way but we flip the
> height.  Ocean terrains aren't eligible for positive-height tiles and
> non-ocean terrains aren't eligible for negative-height tiles (but there
> may be the possibility for freshwater inland lakes via some other
> mechanism).
> 
> So:
> 
> - First generate a height_map.  Note that generators 1-5 in principle
> only differ based on how the height map is created.  The rest can all be
> the same.
> 
> - Create rivers.  Rivers start at a high point and flow downward into
> the ocean.  Rivers must be created before terrains since the terrain
> depends on the water (not the other way around).  If a river can't flow
> down it will carve out a canyon (i.e., decrease the nearby height and
> keep going) or (potentially) fill up a lake and keep going.
> 
> - Create a temperature map.  This is pretty straightforward, except that
> tiles close to the ocean are generally milder (closer to average) than
> those inland, and high tiles are generally colder than low ones.
> 
> - Create a moisture map.  I'm not quite sure how this should be done. 
> Probably you want to calculate prevailing wind direction (based on the
> location of the equator) and simply calculate how "far" each tile is
> from a body of water based on distance and the height of the intervening
> tiles.  Tiles with high altitude are drier.
> 
> - Place terrains, tile by tile.
> 
> Note that the last step is different from the current method.  With the
> current method one terrain type is placed on all tiles, then we move on
> to the next terrain type.
> 
> One thing that isn't accounted for here is clumping.  The current
> algorithm has vegetative terrains (forest, desert) clumped.  One way to
> do this would be to have a second pass that completely recalculates
> everything, but for terrains that clump (which is also a percentage
> given in the ruleset) their likelihood is increased by some factor.
> 
> Another thing I haven't explained is how the server options come into
> play.  These should act to redistribute the values in the maps
> (height_map, moisture_map, temp_map) _before_ assigning terrains.  I'm
> not sure of the exact math, but I can say that with steepness==50 the
> hmap should be unchanged, while with steepness==100 the hmap should end
> up entirely at its maximum while with steepness==0 the hmap should end
> up entirely at its minimum.  Presumably all parameters should be at 0 by
> default.
> 
> Having said all this, I think the first step might be to rewrite gen234
> so that they first create an hmap, then use the same terrain-placement
> routines as gen15.
> 
> jason
> 
This is prety near has i am doing (logic we has speak about it)

but some thing are little different.

the base information are height_map create by one generator or load from
a height_map scenario)
AND
latitude_map create from the actual map_temperature(x,y), that has to be
named map_latitudede(x, y) (from the topology_id) or load from a
scenario with a latitude_map (if not standard projection is proposed by
the scenario maker)

map_x, map_y can't used exept for avoiding singularities.
any time topology_id determine edge wrapping

Then, the scenario can be of different type,
1) classic with a full terrains maps and rivers. (option for specials
and hut)

2)with no map at all.

3) with heigh_map AND/OR latitude_map

TEMPERATURE AND EARTH LIKE MAP


map.temperature with the default value will be 50 and do a temperate
planet, 0 for a very cold and 100 for a very hot. i propose value less
than 30 and more than 70 is reserved for extreme planets.

map.temperature will be used for 2 different things

frist) to split the world in zones (determined by latitude)
polar-cold
temperate
tropical
dry(overlap others)

Second) to be used to determine a middle temperature on all math.

the temperature_map[] will be calculated from latitude_map[] +
map.temperature + near_ocean.

latitude_map[] influence the shape of temperature distribution
map_temperature the midle temperature of earth 
nea_ocean push the temperature to the middle temperature
height_map[] push the temperature to lower ones

finally the temperature map is simplified to some types
frized, cold, temperate, tropical

exact map has to be tuned.

RELIEF OF THE MAP
map.steepnes has a defaul of 50 for a standard map, 0 for a very flat
and 100 for a heigh steepnes map  

this is used to calculate the form height_map[] a simplified
haeight_map, the relief_map[], for land this can get 3 value
flat, hilly, abrupt, tiles to be plased has to match the relief value to
be placed.

Note: the relief_map[] is simple and terrains has not a number height as
proposed by Jason but a relief_type = flat, hilly, abrupt.

This is important, this way the relief map can be tuned in a way
independent of the terrains-set load from rules-set.

WETNESS and RIVERS

First we has to create a base wetness_map[] based on latitude

cold and temperate zones get some wetness, tropical zones get a bonus
wetness, dry zones get a malus wetness.
then heigh sloope tiles get a bonus wetnes (rains in mountains)

form this base wetness we create rivers, rivers has more chance to begin
if tiles are height wetness.    

the amount of rivers can be  maybe calculated from wetness or still
separate option.

finally rivers and water masses are used to put a bonus wetness near
its. and the map_wetness simplified to 3 values, dry, medium, wet

Note there too: the final wetness map has only 3 values, and can be
tuned in a way independent of the terrains rules-set.

PLACING TERRAINS

finally the terrains are one at one (or by littles clusters) from the
rules-set to be placed a terrains has to be the right characteristic
this are

terrain_temperature = (a list)frizzed, cold, temperate, tropical
terrain_wetness = (a list)dry, medium, wet, oceanic
terrain_relief = (a list)flat, hilly, abrupt
note:oceanic terrain can't be wet,dry or medium too.
note: a frizzed terrains can't be cold, temperate or tropical too.

PLACING OTHERS 
Specials can be placed to to match some parameters and not a specific
terrains!

ALL TEMPERATE MAPS has to be has fear as possible (and boring) 

Marcelo