Everest — 3D terrain mesh

This example produces terrain-following 3D surface and volume meshes for the Mount Everest region using a user-defined bounding box and Copernicus GLO-30 DEM tiles. The workflow is identical to the Mont Blanc example but covers a larger area (four DEM tiles) and uses UTM zone 45N.

Features highlighted:

prepare_dem with a four-tile domain
geoms_to_msh_3d and geoms_to_msh_3d_volume

Aspect ratio
The domain spans ~84 km × ~66 km horizontally; Everest is 8,849 m tall. The true aspect ratio is roughly 1:9 — apply vertical exaggeration in your visualiser to make the topography visible.

Everest (3D terrain)

using GeoGmsh

data_dir = joinpath(@__DIR__, "..", "data")
mkpath(data_dir)

Bounding box

Domain of interest with a small padding: original box: 86.551666, 27.712710, 87.301483, 28.214870

lon_min, lat_min = 86.50, 27.66
lon_max, lat_max = 87.35, 28.26
bbox = (lon_min, lat_min, lon_max, lat_max)

bbox_path = joinpath(data_dir, "everest_bbox.geojson")
open(bbox_path, "w") do io
  write(io, """
{
  "type": "FeatureCollection",
  "features": [{
    "type": "Feature",
    "geometry": {
      "type": "Polygon",
      "coordinates": [[[$(lon_min),$(lat_min)],[$(lon_max),$(lat_min)],
                        [$(lon_max),$(lat_max)],[$(lon_min),$(lat_max)],
                        [$(lon_min),$(lat_min)]]]
    },
    "properties": {}
  }]
}
""")
end

Prepare DEM

Four 1°×1° tiles cover the padded domain: latitude bands N27 and N28, longitude columns E086 and E087. prepare_dem downloads, mosaics, and reprojects them to UTM zone 45N (EPSG:32645) in one call.

dem_tif_utm = prepare_dem(
  bbox, "EPSG:32645",
  joinpath(data_dir, "everest_dem_32645.tif");
  source   = :cop30,
  dest_dir = data_dir,
)

3D terrain meshes

A depth of 1,000 m gives a thin but clearly visible pedestal relative to the ~6,000 m of vertical relief in the domain.

output = joinpath(data_dir, "everest")

geoms_to_msh_3d(
  bbox_path, dem_tif_utm, output;
  target_crs   = "EPSG:32645",
  simplify_alg = MinEdgeLength(tol = 500.0),
  mesh_size    = 500.0,
  nodata_fill  = 0.0,
  verbose      = true,
)

geoms_to_msh_3d_volume(
  bbox_path, dem_tif_utm, output * "_volume";
  target_crs   = "EPSG:32645",
  simplify_alg = MinEdgeLength(tol = 500.0),
  mesh_size    = 500.0,
  depth        = 1_000.0,
  nodata_fill  = 0.0,
  verbose      = true,
)

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