Have you ever brought a Google Earth surface into your Civil 3D drawing and it comes in at the wrong elevation? Now, I’m not tallking off by 50′ (well maybe if you’re in Florida) but drastically off. I did a test and in Google Earth, I zoomed in on Longs Peak, one of the 14,000′ mountains visible from my house. In C3D, I set an appropriate coordinate system, import the surface, and everything works. Here’s a screenshot of the surface properties:

However, in two other drawings, using the exact same coordinate systems, the elevations are drastically different:

Now, what on earth could be causing such a drastic change in the elevations? It’s almost like the elevations on the left are being scaled by the conversion factor from feet to meters and on the right the conversion factor from feet to inches, and that’s exactly what is happening. It’s using the drawing units, the AutoCAD drawing units, to scale the Google Earth surface elevations (which units are in meters) as it brings it into the drawing.

In the above image, the left surface was brought into the drawing with units set to unitless (INSUNITS=0) so the elevations are set to meters, since that’s the units Google Earth uses. On the right, the drawing units are set to inches (INSUNITS=1), so that’s how many inches high Longs Peak is. If you are working in an imperial drawing, i.e., your Civil 3D units are set to feet, then you must have the AutoCAD drawing units also set to feet (INSUNITS=2). If you are working in a metric drawing, i.e. your Civil 3D units are set to meters, then you must have the AutoCAD drawing units set to meters (INSUNITS= 6).

Thanks Jeff for letting me know about this one!