| Extension | 123DX |
| Full Name | Autodesk 123D |
| Type | CAD |
| Mime Type | application/octet-stream |
| Format | Binary |
The 123D Design application uses the 123DX file format, which is a Computer Aided Design (CAD) graphics format. Developed by Autodesk, 123D Design was intended as an easy-to-use CAD application aimed at entry-level and enthusiast designers.
123D Design has since been retired, with users moving to other CAD applications such as Fusion 360. The 123DX format is a ZIP container format containing various data files describing the properties of the various objects within the CAD file. Elements such as lines, curves, and 3D volumes such as cubes and cylinders are all stored within human-readable text files wrapped within a compressed ZIP file containing the 123DX file extension.
As mentioned, the 123D Design software has been superseded by other, more capable CAD software, meaning support for editing the file is limited. The original 123D design software can still be downloaded and contains numerous options to export data to standard formats, such as STEP and STL.
The OBJ file format is a 3D graphics file format used to define complex 3D models, including geometry, materials, and textures. OBJ files are text files, making them human-readable and easy to modify by hand. The downside to this ease of readability is that the files can become rather large when dealing with large or complex 3D models.
As mentioned, the OBJ format stores not only 3D model geometry but also materials and textures. These materials are usually defined in a separate file with the MTL file extension and specify geometry rendering details such as diffuse and specular colour, transparency, and much more.
The OBJ material file can also reference external texture files. These are usually JPEG or PNG files; however, these can be older formats, such as TGA. Where materials are used, the OBJ file will also contain material names preceding the geometry faces they should be applied to. If textures are referenced, the geometry will also contain texture coordinates (UV) for each vertex.
