From GPR DZT files to a CAD plan: formats, coordinates and deliverables

GSSI DZT, DZG and DZX files, GNSS positioning, British National Grid with OSTN15, NAD83(2011) / UTM, and DXF, CSV and GeoJSON deliverables: the full path from GPR survey to plan.

The files in a GSSI survey

DZT: the measurement file. A header describes the acquisition (antenna, time window, samples, scans per metre), followed by the traces. Dual-frequency antennas such as the UtilityScan DF record two channels in one file, each with its own header.
DZG: the GNSS log. It ties scan numbers to NMEA position sentences — that is what places every trace on the ground.
DZX: metadata and the marks placed during acquisition.

Processing needs the raw files, not image exports: a screenshot loses amplitude, polarity and the geometry of the acquisition.

With or without GNSS

With a fixed RTK GNSS solution every trace gets a position to the centimetre, and the plan comes out georeferenced straight away. The position just has to be interpolated between NMEA sentences, taking the local direction of the line into account.

Without GNSS, the survey is positioned by the survey wheel and the setting out of the lines. The plan is then delivered on the survey's local grid, to be tied in to known points afterwards. An assumption has to be made about line direction (back and forth, or always the same way): it is worth writing it down on site.

The right coordinate system

In Great Britain the national system is British National Grid (EPSG:27700). The official transformation from GNSS coordinates uses the OSTN15 grid; a simple seven-parameter shortcut can be out by a metre or more, which shows as soon as the plan is overlaid on existing mapping.

In the US, GNSS positions are close to WGS84, while engineering plans are usually on NAD83. The two now differ by roughly one to two metres across the continental US, so the datum must be stated and converted properly — for example NAD83(2011) / UTM (EPSG:6339 to 6348).

GeoJSON always stays in WGS84 (longitude, latitude): the easiest format for checking a result on an online map or in QGIS.

The deliverables

DXF: every utility as a 3D polyline, on separate layers by confidence level, with the GPR lines on a layer of their own. It opens in AutoCAD, Civil 3D, BricsCAD or QGIS.
CSV: a table of utilities with minimum and maximum depth, length, uncertainty and confidence level.
GeoJSON: the same information for GIS tools.
PDF report: plan, table, ground velocity estimated from the data and the one entered by the operator.

With Radar Plan 3D

You upload a .zip archive with the .DZT files, plus the .DZG files if the survey was positioned. The coordinate system is chosen automatically from the location: British National Grid with OSTN15 in Great Britain, NAD83(2011) / UTM in the US. The cost is shown before processing, raw files are deleted from the server as soon as it ends, and results stay available for 30 days. MALA, Sensors & Software and IDS formats are in preparation.

Updated 23 Oct 2026