Photogrammetry

BEGINNER

📖3 min read

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Creating accurate 3D models from multiple photographs.

Key Concepts

• Photo acquisition
• Point cloud generation
• Mesh reconstruction
• Texture extraction

COLMAP

COLMAP is an open-source, research-grade photogrammetry pipeline. It's the academic foundation that many other tools build upon. It's highly accurate, well-documented in scientific literature, but:

• Command-line focused (though there is a GUI)
• Requires more technical knowledge to use effectively
• Free and open-source
• Often used as a preprocessing step or for custom pipelines

Meshroom

Meshroom is essentially a user-friendly graphical wrapper built on top of the AliceVision photogrammetry framework, which itself draws heavily on COLMAP's methodologies. It's:

• Free and open-source
• Node-based visual interface (less intimidating than command-line)
• Great for learning and experimenting
• More accessible for beginners

RealityCapture & Metashape

These are commercial, production-grade tools optimized for speed and handling large datasets:

• RealityCapture: Known for being extremely fast (GPU-accelerated), popular in game development and surveying
• Metashape (formerly PhotoScan): Industry standard in archaeology, forensics, and professional surveying; very reliable and well-supported

The relationship: COLMAP pioneered many algorithms (Structure from Motion, Multi-View Stereo) that the others use or build upon. Meshroom democratizes these techniques with a GUI. RealityCapture and Metashape take the core concepts and optimize them for professional workflows with better performance, automation, and support.

For forensics: Many practitioners use RealityCapture or Metashape for the initial 3D reconstruction (speed, reliability), then bring the resulting mesh into Blender for measurement, annotation, and presentation.

Photogrammetry Importer add-on

The Blender Photogrammetry Importer add-on is specifically designed to import COLMAP reconstruction data directly into Blender.

The Relationship

COLMAP outputs several file formats during its photogrammetry reconstruction process:

• Camera positions and orientations (where each photo was taken from)
• Sparse point clouds (initial 3D feature points)
• Dense point clouds (more detailed reconstruction)
• Project files with all this spatial data

The Photogrammetry Importer add-on reads these COLMAP output files and translates them into Blender's native format, allowing you to:

• Visualize camera positions as objects in 3D space
• Import the point cloud as geometry
• Understand the spatial relationships between photos and the reconstructed scene
• Use the camera data for further analysis or visualization

Why This Matters for Forensics

This connection is valuable because:

1. You can use COLMAP's robust algorithms for the heavy lifting of photogrammetry processing
2. Then bring the results into Blender for measurement, annotation, and presentation
3. You get the best of both worlds: COLMAP's accuracy and Blender's visualization/synthesis capabilities

The add-on also supports other photogrammetry software outputs (like Meshroom's AliceVision format), but COLMAP support is central because COLMAP is the open-source standard that many workflows are built around.

In practice: Process your crime scene photos in COLMAP ? Import the reconstruction into Blender with the add-on ? Add measurements, annotations, and other evidence sources ? Create your final presentation.

Workflow

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Best Practices

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Common Pitfalls

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