Processing orthophotomap

2025-09-07 · by toon

#guide

This is a summary of all the steps I did to process the orthophotomap

I downloaded the orthophotomap from here

Dilsen-Stokkem is code 72041

The download contains a jp2 file of 900MB

Qgis

With qgis you view the map

Create tiles

I converted the jp2 files to tiles using the following commands

Create a tif file

Crop using Lambert72 bounds, reproject to Web Mercator

gdalwarp \
  -te_srs EPSG:31370 \
  -te 244492 188891 245434 190782 \
  -t_srs EPSG:3857 \
  -r bilinear \
  -dstalpha \
  -co TILED=YES -co COMPRESS=JPEG -co BIGTIFF=YES \
  OMWRGB25VL_72041.jp2 track_3857.tif

Create multi level tiles

gdal2tiles.py --xyz -z 17-20 -r bilinear -w none \
  hometown_3857.tif tiles_xyz

convert to jpg

#!/usr/bin/env bash
# Build XYZ tiles from a raster using GDAL, then convert PNG tiles to JPEG and remove PNGs.
# Defaults: z=17-19, tilesize=512, resampling=near, quality=80, processes=$(nproc)
# Usage:
#   ./build_xyz_jpeg_tiles.sh <input.tif> <output_dir> [zoom_levels]
# Example:
#   ./build_xyz_jpeg_tiles.sh hometown_3857.tif tiles_xyz_512_jpeg 17-19

set -euo pipefail

# ---- Inputs & defaults ----
INPUT="${1:-}"
OUT_DIR="${2:-}"
ZOOM="${3:-17-19}"

TILESIZE="${TILESIZE:-512}"
RESAMPLING="${RESAMPLING:-near}"       # near | bilinear | cubic | lanczos ...
QUALITY="${QUALITY:-80}"               # JPEG quality 1..100
PROCESSES="${PROCESSES:-$(nproc)}"

if [[ -z "$INPUT" || -z "$OUT_DIR" ]]; then
  echo "Usage: $0 <input.tif> <output_dir> [zoom_levels]"
  echo "Env overrides: TILESIZE=${TILESIZE} RESAMPLING=${RESAMPLING} QUALITY=${QUALITY} PROCESSES=${PROCESSES}"
  exit 1
fi

# ---- Dependency checks ----
command -v gdal2tiles.py >/dev/null 2>&1 || { echo "Error: gdal2tiles.py not found in PATH."; exit 1; }
command -v mogrify >/dev/null 2>&1 || { echo "Error: mogrify (ImageMagick) not found in PATH."; exit 1; }
command -v find >/dev/null 2>&1 || { echo "Error: find not available."; exit 1; }
command -v xargs >/dev/null 2>&1 || { echo "Error: xargs not available."; exit 1; }

# ---- Build PNG XYZ tiles with GDAL ----
echo "==> Tiling with GDAL"
echo "    Input:      $INPUT"
echo "    Output dir: $OUT_DIR"
echo "    Zoom:       $ZOOM"
echo "    Tilesize:   $TILESIZE"
echo "    Resampling: $RESAMPLING"
echo "    Processes:  $PROCESSES"

mkdir -p "$OUT_DIR"
gdal2tiles.py --xyz -z "$ZOOM" \
  --tilesize="$TILESIZE" \
  --processes="$PROCESSES" \
  -r "$RESAMPLING" -w none \
  "$INPUT" "$OUT_DIR"

# ---- Convert PNG -> JPEG in place ----
echo "==> Converting PNG -> JPEG (quality=$QUALITY) using $PROCESSES processes"
# Only attempt conversion if there are PNGs
if find "$OUT_DIR" -type f -name '*.png' -print -quit | grep -q .; then
  # Use mogrify to write .jpg next to each .png
  # -print0/-0 handles spaces/newlines safely; -P parallelizes conversion.
  find "$OUT_DIR" -type f -name '*.png' -print0 \
    | xargs -0 -P "$PROCESSES" mogrify -format jpg -quality "$QUALITY"

  echo "==> Removing original PNG tiles"
  find "$OUT_DIR" -type f -name '*.png' -delete
else
  echo "No PNG tiles found to convert—nothing to do."
fi

echo "==> Done."
echo "JPEG tiles are in: $OUT_DIR"