DTM and TIN Files, Explained
A DTM is a digital terrain model, and a TIN is a triangulated irregular network used to represent a surface with connected triangles. The terms describe model concepts, not one universally compatible file format. Ask which application created the model and which exchange format the receiving tool accepts.
Terrain model and triangle network
A terrain model represents ground elevations. In a TIN, points with coordinates and elevations form triangles, allowing the model to represent a surface between those points. Source data, boundaries, and the way the model was built affect the result.
The native file format depends on the application. A surface stored in a design project may need to be exported before another tool can read it. LandXML is one exchange option where both applications support the required surface data.
What to check when models change hands
Identify whether the model represents existing ground, proposed finished grade, subgrade, or another surface. Obtain the revision, units, coordinate reference, and included boundary with the file.
When a quantity depends on comparing surfaces, retain the source and settings for each. Compare their extents and elevations. A PDF showing contours depicts the surface; the terrain model contains the underlying data.
Request a compatible surface model
- 1
Ask the sender for the named surface, its revision, and the application that created it.
- 2
Confirm a supported exchange format with the receiving application. Request LandXML only when it supports the needed entities.
- 3
Obtain units and coordinate-reference information along with the file.
- 4
Check the imported location, elevations, and boundaries against the issued information before calculating quantities.
Using this file with CivilTakeoff
CivilTakeoff measures 2D quantities from plan PDFs and aerial imagery; it does not import DTM or TIN terrain models or calculate volumes between surfaces.
Frequently asked questions
Are DTM and TIN interchangeable terms?
They are related but describe different things: DTM describes a terrain model, while TIN describes a triangle-based representation of a surface.
Does a PDF contain the original TIN?
A plotted plan generally shows contours and spot elevations rather than the editable surface model. Request the model from its source when you need that data.
What file should I request?
Ask for an export of the named surface in a format your receiving tool supports, with units, coordinate reference, and revision.