What is the 3D file format?
A .3d file is the compiled output of the Survex cave survey software, storing processed three-dimensional data for underground cave systems. The relationship to Survex source files (.svx) is analogous to source code and a compiled binary: .svx files are authored by surveyors, and the cavern program compiles them into a .3d file.
The file begins with a plain-text ASCII header: the string Survex 3D Image File at byte offset 0, followed by a version identifier (e.g., v8) and metadata including the coordinate system as a PROJ string and a Unix timestamp. The remainder of the file is binary, encoding survey stations (XYZ coordinates), survey legs (connections between stations), passage walls via LRUD (Left/Right/Up/Down) measurements, and cross-sections.
Version v8 is the current format, adding improved coordinate system support via PROJ strings. Earlier versions v3-v7 are documented in Survex's legacy format specification. The Aven viewer (bundled with Survex) renders .3d files as interactive 3D cave passage models. Therion, the other major open-source cave survey application, imports .3d files directly.
Survex's export tools can convert .3d to .dxf, .kml, SVG, or CSV for use in CAD or mapping software.
Note: the .3d extension is shared by several unrelated formats; the Survex cave survey file is identified by its Survex 3D Image File ASCII text header.
Security & safety
RISK: LOWBinary data file with no executable content. Safe to open in Survex.
Format details
in a nutshell- VersaCAD 3D Drawing - VersaCAD (Archway Systems) uses .3d for its native 3D CAD drawing format; unrelated to cave survey.
- quick3D / generic 3D model export - Various older 3D tools (quick3D, 3D Object Converter) use .3d as a generic export extension for simple 3D mesh data.
- Cadwork 3D architectural/timber construction model - Cadwork uses .3d for its proprietary 3D construction project files (timber/concrete structures).
Programs that open 3D files
Windows2 apps
Survex (includes Aven viewer)
Open-source Open Aven (bundled with Survex), then File > Open .3d file. Provides full 3D interactive view with rotation, zoom, and export. 
macOS1 app
Survex (includes Aven viewer)
Open-source Open Aven, File > Open .3d. Survex is available for macOS via Homebrew or direct download. 
Linux1 app
Survex (includes Aven viewer)
Open-source Install via package manager (apt install survex); run aven file.3d. Technical details
deep spec| File signature | ASCII text "Survex 3D Image File" at byte offset 0, followed by newline (0x0A) |
| Version identifier | Second header line: version string (e.g., v8, v7, v3) |
| Header format | Plain-text ASCII: magic string, version, PROJ coordinate system string, Unix timestamp, flags byte |
| Data section encoding | Binary block stream following the ASCII text header |
| Byte order | Little-endian |
| Current format version | v8 (adds PROJ string coordinate system support and improved metadata) |
| Survey data stored | Survey stations (XYZ), legs (inter-station connections), LRUD passage walls, cross-sections, station labels |
| Coordinate system | Embedded PROJ string in v8 header; earlier versions used simpler coordinate metadata |
| Typical file size | 10 KB - 10 MB (complex multi-thousand-station systems may reach tens of MB) |
| Platform | Windows, Linux, macOS |
| Relationship to SVX source | .3d is the compiled result of .svx survey source files processed by the cavern program |
| Primary viewer | Aven (bundled with Survex): interactive 3D passage rendering and measurement |
| Export targets | DXF, KML, SVG, CSV via Survex's built-in export tools |
| Third-party import | Therion cave survey software imports .3d files directly |
| Released | 1991 (Survex project first release) |
| Latest version | Version 8 (v8; current as of Survex 1.4.x) |
| Open standard | Yes · royalty-free |
| Specification | survex.com |
3D conversions
Community Q&A
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