decimate_stl.bash

#!/usr/bin/env bash
# Clean up and decimate all STL files in a folder using MeshLab.
# Usage: ./decimate_stl.sh <input_dir> <output_dir>

set -euo pipefail

if [ $# -lt 2 ]; then
    echo "Usage: $0 <input_dir> <output_dir>"
    exit 1
fi

INPUT_DIR="$1"
OUTPUT_DIR="$2"

mkdir -p "$OUTPUT_DIR"

# Write the MeshLab filter script to a temp file
MLX=$(mktemp /tmp/decimate_XXXXXX.mlx)
cat > "$MLX" <<'EOF'
<!DOCTYPE FilterScript>
<FilterScript>

 <!-- 1. Weld near-coincident vertices to collapse overlapping surfaces -->
 <filter name="Remove Duplicate Vertices"/>
 <filter name="Merge Close Vertices">
  <Param name="Threshold" type="RichAbsPerc" description="Merging distance" tooltip="" value="0.0001" min="0" max="0"/>
 </filter>

 <!-- 2. Remove degenerate/duplicate geometry (after merge so overlaps are caught) -->
 <filter name="Remove Duplicate Faces"/>
 <filter name="Remove Zero Area Faces"/>

 <!-- 3. Fix topology -->
 <filter name="Repair non Manifold Edges by removing faces"/>
 <filter name="Repair non Manifold Vertices by splitting">
  <Param name="VertDispRatio" type="RichFloat" description="Vertex Displacement Ratio" tooltip="" value="0"/>
 </filter>

 <!-- 4. Remove floating fragments (less than 25 faces) -->
 <filter name="Remove Isolated pieces (wrt Face Num.)">
  <Param name="MinComponentSize" type="RichInt" description="Enter minimum conn. comp size:" tooltip="" value="25"/>
  <Param name="removeUnref" type="RichBool" description="Remove unfreferenced vertices" tooltip="" value="true"/>
 </filter>

 <!-- 5. Clean up any orphaned vertices -->
 <filter name="Remove Unreferenced Vertices"/>

 <!-- 6. Decimate -->
 <filter name="Simplification: Quadric Edge Collapse Decimation">
  <Param name="TargetFaceNum" type="RichInt" description="Target number of faces" tooltip="The desired final number of faces." value="3000"/>
  <Param name="TargetPerc" type="RichFloat" description="Percentage reduction (0..1)" tooltip="If non zero, this parameter specifies the desired final size of the mesh as a percentage of the initial size." value="0"/>
  <Param name="QualityThr" type="RichFloat" description="Quality threshold" tooltip="Quality threshold for penalizing bad shaped faces." value="0.3"/>
  <Param name="PreserveBoundary" type="RichBool" description="Preserve Boundary of the mesh" tooltip="" value="false"/>
  <Param name="BoundaryWeight" type="RichFloat" description="Boundary Preserving Weight" tooltip="" value="1"/>
  <Param name="PreserveNormal" type="RichBool" description="Preserve Normal" tooltip="" value="false"/>
  <Param name="PreserveTopology" type="RichBool" description="Preserve Topology" tooltip="" value="false"/>
  <Param name="OptimalPlacement" type="RichBool" description="Optimal position of simplified vertices" tooltip="" value="true"/>
  <Param name="PlanarQuadric" type="RichBool" description="Planar Simplification" tooltip="" value="false"/>
  <Param name="PlanarWeight" type="RichFloat" description="Planar Simp. Weight" tooltip="" value="0.001"/>
  <Param name="QualityWeight" type="RichBool" description="Weighted Simplification" tooltip="" value="false"/>
  <Param name="AutoClean" type="RichBool" description="Post-simplification cleaning" tooltip="" value="true"/>
  <Param name="Selected" type="RichBool" description="Simplify only selected faces" tooltip="" value="false"/>
 </filter>

 <!-- 7. Recompute normals after all modifications -->
 <filter name="Re-Compute Face Normals"/>
 <filter name="Re-Compute Vertex Normals">
  <Param name="weightMode" type="RichEnum" description="Weighting Mode:" tooltip="" value="2" enum_val0="Simple Average" enum_val1="By Area" enum_val2="By Angle" enum_val3="As defined by N. Max"/>
 </filter>

</FilterScript>
EOF

trap 'rm -f "$MLX"' EXIT

count=0
for stl in "$INPUT_DIR"/*.stl "$INPUT_DIR"/*.STL; do
    [ -f "$stl" ] || continue
    name="$(basename "$stl")"
    echo "Decimating: $name"
    meshlabserver -i "$stl" -o "$OUTPUT_DIR/$name" -s "$MLX"
    count=$((count + 1))
done

echo "Done. Decimated $count file(s) into $OUTPUT_DIR"