Ocean support, and world wide support

[jetelain]

• Compute ocean polygon based on OpenStreetMap coastline
• Use elevation from SRTM15+ for ocean depth and ensure depth below zero for ocean
• Specific ocean ground material
  • By default, add sand on coastline on +/- 5 m (with a fade effect)
  • Low priority to allow manually mapped rock and sand area to be shown
• Use SRTM15+ / AW3D30 for regions not covered by SRTM1

[jetelain]

Current result is not really great due to elevation grid.

Should try to have a smoother transition between the two height maps, ideas to test :

• use mask as a coef between the two height map
• Reduce max -0.25 / min +0.25 for each height maps instead of max -1 / min +1
• draw land with an halo effect (but implies to keep land polygons) (instead of drawing ocean)

[jetelain]

Preview:

[jetelain]

Should also change outside texture is the map is an island