Tiny Online Tools
Getting a reconstruction out of COLMAP
A COLMAP model is three binary files that only COLMAP-aware software can read. A GLB opens in Blender, Windows 3D Viewer, macOS Quick Look, Unity, Unreal, three.js, Babylon and every glTF page on the web. Exporting one is how you show a reconstruction to somebody who does not have COLMAP installed — or drop it into a scene next to the model it was used to build.
What goes into the file
Sparse points as a glTF POINTS primitive with positions and colours. COLMAP's RGB is sRGB and glTF's COLOR_0 is linear, so it is converted on the way out.
Camera frusta as LINES: four corner rays from the optical centre, the rectangle joining them, and a notch on the top edge showing the roll of each shot. The corner directions come from the real intrinsics, so a wide lens draws a wide frustum.
Real glTF cameras — a perspective camera node per image, with yfov from the COLMAP intrinsics and the right aspect ratio, each named after its source photograph. Blender imports them as actual cameras you can look through, and the outliner reads as a list of your filenames rather than Object.001.
The conversion, stated plainly
COLMAP is RDF — x right, y down, z forward. glTF is RUB — x right, y up, z back. Every position and every direction in the export is converted between the two. That single omission is why so many home-made COLMAP exports open upside down in Blender.
The other half: COLMAP stores the pose world-to-camera, so a camera's place in the world is −Rᵀt, not t.
One caveat worth knowing
Point primitives are valid glTF but not universally drawn — Windows 3D Viewer, among others, shows nothing for them. Blender, three.js and Babylon are fine. If you need something that renders everywhere, turn on the solid camera markers.
Everything runs in your browser; the reconstruction is never uploaded.