laz2geotiff

Builds seamless digital terrain models from airborne lidar point clouds (*.laz). It is how Freemap's terrain sources for terrain-tiles are made from national lidar sets, which come as thousands of flight-line files.

Commands

Command	What it does
index	Scans a directory of *.laz files into a sqlite index of their bounding boxes.
xyz	Renders the points straight onto the Web Mercator XYZ pixel grid of one zoom, as Int32 height steps, one GeoTIFF per block. This is the source format terrain-tiles reads.
fill	Fills the gaps an xyz render leaves, seamlessly across blocks.
render	The older path: grids the points in the source CRS as Float32 tiles plus a VRT.

laz2geotiff <command> --help lists every option.

xyz

Points are reprojected through a PROJ pipeline (--ct, a file holding the pipeline from the source CRS to EPSG:3857, sampled on a bilinear grid of exact transforms), triangulated per tile of --tile-zoom plus --margin, and each pixel is interpolated by natural neighbours (Sibson) over the Delaunay triangulation.

• Seamless without a global triangulation. A tile sees the points of its margin too, so neighbouring tiles see the same triangles near their shared edge and interpolate it identically.
• Gaps. A triangle whose longest edge is over --gap-cap (EPSG:3857 metres), or over --gap-factor times the local median edge, is left as nodata for fill; natural neighbours would bulge across it. --gap-factor 0 keeps only the absolute cap. The margin must exceed the cap, or two tiles may triangulate a gap differently.
• Blocks. Work goes in blocks of --block-zoom. A block's points are read once and held in RAM, then its tiles render in parallel into one file. The next block's points are read on their own --read-jobs threads while the current one renders. A block file appears only once complete and is recorded in blocks.done, so an interrupted run resumes where it stopped.
• Reading. A flight line is far longer than a block, so the first read of a file records each LAZ chunk's box (chunks.sqlite in the output directory), and later blocks decode only the chunks that reach them. Only x, y, z and the class are decoded, and only --classes are kept.
• Memory. Before a tile starts, a gate estimates its need from its point count and waits while that would leave less than --mem-reserve GB of the system's available memory. <out-dir>/limits, holding <jobs> <reserve GB>, overrides both and is re-read before every tile, so a running render can be throttled without a restart.

Heights are stored in --step metres (2 mm by default), with the scale set on the band, and nodata is i32::MIN.

fill

A membrane (Laplace) fill. A coarse field of the whole mosaic at --coarse-zoom supplies each block window's outer edge, so a gap spanning several blocks, such as a reservoir, is filled as one surface. A gap enclosed by data is filled whole; one open to the edge of the data only within --reach metres of it.

Blocks are filled independently, so their edges can disagree slightly. A second pass with --boundary (a VRT of the first pass's output) takes each window's edge from that result instead, and the seams disappear.

Example: Slovakia at z18

L=target/release/laz2geotiff

$L index /data/sk/laz sk-index.sqlite

# Ground points only; natural neighbours everywhere except gaps over 100 m.
$L xyz --index sk-index.sqlite --ct ct_sk.txt --out-dir blocks \
  --zoom 18 --block-zoom 13 --tile-zoom 16 --classes 2 \
  --margin 120 --gap-factor 0 --gap-cap 100 --jobs 24 --read-jobs 8

gdalbuildvrt blocks.vrt blocks/*.tif
$L fill --input blocks.vrt --blocks blocks --out-dir fill1
gdalbuildvrt fill1.vrt fill1/*.tif
mkdir -p fill2 && cp fill1/coarse_z12.f32 fill2/   # reuse the coarse field
$L fill --input blocks.vrt --blocks blocks --out-dir fill2 --boundary fill1.vrt

The filled blocks are then clipped to a cutline, merged into one GeoTIFF with gdal_translate, and given overviews with gdaladdo -r average.

Building

cargo build --release

It builds with jemalloc and for the native CPU by default (.cargo/config.toml), so the binary will not run on an older CPU than the one it was built on. Needs GDAL and PROJ.

Licence

GPL-3.0-or-later; see LICENSE.