PLY is what scanners and photogrammetry pipelines write. OBJ is what modelling tools want. This is the bridge.
PLY is the native output of most 3D scanners, photogrammetry software and point-cloud tools — RealityCapture, Meshroom, Polycam, structured-light scanners. It handles per-vertex colour, which is exactly what a scanner captures and exactly what STL cannot store.
Converting to OBJ gets you into Blender, ZBrush, Maya and 3ds Max. Note that vertex colours do not survive the trip: OBJ carries colour through a separate .mtl material file and texture images, not per vertex. If the colour matters, keep the PLY alongside and bake it to a texture in your modelling tool.
Scanned geometry arrives with holes where the scanner could not see, stray floating fragments and inconsistent normals. We merge duplicate vertices on the way through, but we deliberately do not silently reshape your scan.
If you need it watertight for printing rather than editing, run it through STL repair or convert straight to a printable mesh.
Every converter runs the same geometry engine — see all 20 conversions.