use map functions in a worker?

[pcace]

Hi there,

i am not quite sure if its the right place to ask, if not, i am sorry ;)

i am using maplibre in a project where i have to calculate some long(er) running processes which depend on the current loaded terrain in the viewport. On each resolution change of the terrain i get a nasty block of the main thread.
a simple function would be something like this (a lot of times ;) ):

export function queryTerrainAltitude(map: Map, lngLat: LngLat, zoom = 20) {
  const curExaggeration = map.terrain.exaggeration * 1
  map.terrain.exaggeration = 1
  const altitude = map.terrain.getElevationForLngLatZoom(lngLat, zoom)

  map.terrain.exaggeration = curExaggeration
  return altitude
}

that works nice as expected.

the issue i cannot get my head around is, that i need this kind of a function in a worker. i need the current map in the worker to do some calculation which depend on for example the current terrain.

since i cannot convert map into a transferable object how would i do that? Is there any kind of shared memory available to use for thinks like that?

I am sure someone had a similar problem and can share how i would have to deal with this problem.

thanks a lot,

pcace

[HarelM]

You either need to pass the relevant data to the worker to do the calculations or store it in the worker and then query it.
The map is constantly communicating with workers to achieve this kind of behavior.

[pcace]

Hi, thanks for your fast reply!
do you have any hint where i would need to look to get the current terrain (especially to calculate map.terrain.getElevationForLngLatZoom(lngLat, zoom)) into a worker?
Thanks a lot

[HarelM]

Checkout https://github.com/maplibre/maplibre-gl-js/blob/main/src/data/dem_data.ts
It is related to reading terrainRBG tiles and getting the elevation out of them.

[HarelM]

Also RasterDEM related code (it exists both in the worker and in the main thread, and passes the data around).
This is what is responsible for hillshading basically.