kirra-docs

Surpac DTM / STR Import

Kirra imports Surpac surface files as triangulated 3D surfaces. The Surpac format uses a paired-file system: an STR file containing vertex coordinates and a DTM file containing triangle topology.

Screenshot coming soon

How to Import

Click File > Import
Select both your .dtm and .str files together
Both files must share the same base filename (e.g., terrain.dtm + terrain.str)
The surface appears in the TreeView and is visible in both 2D and 3D views

File Pair

File	Contains	Example
`.str` (String)	Unique vertex coordinates (X, Y, Z)	`terrain.str`
`.dtm` (Digital Terrain Model)	Triangle connectivity (which vertices form each triangle)	`terrain.dtm`

Both files are required – the DTM references vertex positions defined in the STR.

Coordinate Order

Important: Surpac files store coordinates as Northing (Y), Easting (X), Elevation (Z) – the opposite of the typical X, Y, Z convention. Kirra handles this swap automatically on import and export.

STR File Format

The STR file stores unique 3D vertices with 1-based indexing:

filename, dd-Mmm-yy,,description
0, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000
32000, Y1, X1, Z1,
32000, Y2, X2, Z2,
...
0, 0.000, 0.000, 0.000, END

String number 32000 indicates surface vertices
Each vertex appears exactly once (no duplicates)
Terminated by an END marker

DTM File Format

The DTM file defines how vertices connect to form triangles:

filename.str,
0, 0.000, 0.000, 0.000, END
OBJECT, 1,
TRISOLATION, 1, neighbours=no,validated=true,closed=no
1, 2, 3, 1, 0, 0, 0,
2, 3, 4, 1, 0, 0, 0,
...
END

Each triangle line contains: Triangle ID, Vertex 1, Vertex 2, Vertex 3, and three neighbour references (0 = boundary edge).

After Import

Once imported, the surface is available for:

Gradient colouring (elevation, hillshade, scientific colour maps)
Boolean operations with other surfaces
Grade control (apply surface elevation to blast holes)
Contour generation
GeoTIFF export
Blast analytics overlay

Exporting Back to Surpac

You can export surfaces back to Surpac format via File > Export > Surpac DTM (Surfaces). Kirra generates both .dtm and .str files with vertex deduplication and proper 1-based indexing.

Troubleshooting

Problem	Solution
“Missing files” error	Both .dtm and .str files must be selected together and share the same base filename
Surface appears empty	Check that the DTM file references valid vertex indices from the STR file
Coordinates look wrong	Verify your Surpac files use the expected Northing/Easting order