Contours: intervals, datums, and CAD export

Contours are lines that connect points of equal elevation. DroneFlow derives them from the terrain model, so they follow the real ground, and you control the interval.

Choosing an interval

A tighter interval (say 1 ft) shows fine grade but crowds a busy site; a wider interval (5 ft) reads cleanly for an overview. Pick the interval that matches how the drawing will be used.

Datum matters

Contour elevations are only meaningful against a known vertical datum. When you choose a vertical datum at upload, DroneFlow converts elevations to orthometric height on that datum — which is what most site and civil work expects — NAVD88 (GEOID18) in the US, or EGM2008 anywhere in the world. Keep them “as delivered” and they stay on whatever reference your export carried (often ellipsoidal); the project page labels which. See coordinate systems and datums.

Getting them into CAD

Contours export as CAD-ready vectors (DXF/SHP) so they drop straight into your drawing, alongside the orthomosaic as a reference image.

When you need a surface, not lines

Contours are for looking at; a surface is what a machine can be given. Every project also ships the measured ground as a LandXML TIN — the format Civil 3D, Trimble Business Center, Carlson and grade-control boxes read. If you uploaded a design surface you also get a distance-to-grade surface beside it, where positive means the ground sits above design and has to be cut to reach it. Both come out on the same CAD export grid as your DXF, so one delivery cannot arrive on two different grids.