Terrarium-encode an elevation grid to RGBA bytes (1/256 m granularity).
Row-major elevations in metres, length w*h.
w*h
Grid width in pixels.
Grid height in pixels.
Optional nodata mask + fill; see EncodeOptions.
RGBA Uint8ClampedArray of length w*h*4 (alpha is 255).
Uint8ClampedArray
w*h*4
Terrarium-encode an elevation grid to RGBA bytes (1/256 m granularity).