gmldem2tif

A converter from GML DEM by GSI to GeoTIFF with compression support

Usage

bundle install
bundle exec ruby gmldem2tif.rb [options] input_dir output_dir

Options

• -n, --nproc NUM - Number of parallel processes (default: 1)
• -v, --verbose - Enable verbose output
• -c, --compression TYPE - Compression type: zstd, zstd-max, lzw, deflate, none (default: zstd)

Compression Types

• zstd (default) - ZSTD compression at level 6 with floating-point predictor. Modern, efficient compression with excellent ratio and fast decompression. Requires GDAL >= 3.1. Recommended for most use cases.
• zstd-max - ZSTD compression at level 9 with floating-point predictor. Maximum compression for archival purposes where encoding time is acceptable.
• lzw - LZW compression with floating-point predictor. Legacy compatibility option for older GIS software.
• deflate - DEFLATE compression with floating-point predictor. Legacy compatibility option, alternative to LZW.
• none - No compression. Creates uncompressed TIFF files.

All compressed outputs use:

• PREDICTOR=3: Floating-point predictor optimized for DEM data (FLOAT32)
• Tiling: 512x512 blocks for cloud-optimized GeoTIFFs with efficient partial reads
• Internal tiling: Improves random access and cloud workflows

Why ZSTD?

ZSTD (Zstandard) provides better compression ratios than LZW/DEFLATE while maintaining fast decompression speeds. Level 6 offers an excellent balance between compression time and file size for production workflows. Use zstd-max (level 9) when creating archives where encoding time is less critical.

Examples

# Basic usage with default ZSTD compression (level 6)
bundle exec ruby gmldem2tif.rb -n $(nproc) input_dir output_dir

# Use maximum ZSTD compression for archival
bundle exec ruby gmldem2tif.rb -n $(nproc) -c zstd-max input_dir output_dir

# Use LZW for legacy compatibility
bundle exec ruby gmldem2tif.rb -n $(nproc) -c lzw input_dir output_dir

# Use DEFLATE compression
bundle exec ruby gmldem2tif.rb -n $(nproc) -c deflate input_dir output_dir

# Create uncompressed files
bundle exec ruby gmldem2tif.rb -n $(nproc) -c none input_dir output_dir

# Verbose mode to see compression details
bundle exec ruby gmldem2tif.rb -v -n $(nproc) input_dir output_dir

Docker

docker build -t gmldem2tif .
docker run --rm -u $(id -u):$(id -g) -v /path/to/input_dir:/input -v /path/to/output_dir:/output gmldem2tif /input /output

The Docker image uses ZSTD compression by default. To use different compression options, override the entrypoint:

docker run --rm -u $(id -u):$(id -g) -v /path/to/input_dir:/input -v /path/to/output_dir:/output \
  --entrypoint /bin/bash gmldem2tif \
  -c "bundle exec ruby gmldem2tif.rb -n $(nproc) -c zstd-max /input /output"

Features

• Modern Compression: ZSTD provides better compression ratios than legacy formats while maintaining fast decompression
• Lossless: All compression options preserve elevation data exactly
• Optimized for Floating-Point DEMs: Uses PREDICTOR=3 (floating-point predictor) for FLOAT32 elevation data
• Cloud-Optimized: Tiled output with 512x512 block size for efficient partial reads and cloud workflows
• High Performance: Multi-process parallel processing support
• Flexible: Multiple compression options from maximum compression (zstd-max) to legacy compatibility (lzw/deflate)
• Interoperable: Compatible with GDAL >= 3.1 and all major modern GIS software (QGIS, ArcGIS, etc.)

Requirements

• GDAL >= 3.1 for ZSTD compression support
• For legacy compatibility (older GDAL versions), use -c lzw or -c deflate