While importing surface data from Google Earth is probably the easiest way to get some conceptual topographical data into your drawings, DEM’s have to be a close second. For the uninitiated, DEM’s or Digital Elevation Models could be described as a surface whose data is organized in a grid. This is fundamentally different than DTM’s (standard Civil 3D surface) which still stores a collection of points, but in the form of triangles not a structured grid. The great thing about DEM’s is they’re readily available for FREE from a wonderful website named the Geo Community. Now don’t be fooled when you visit the site as you will see all sorts of premium content; never fear as there’s ample data that can be had for free!
For one reason or another drawings sometimes need to be moved from one coordinate system (datum) to another. A classic example may be moving from a NAD 27 datum to a NAD 83. Whatever the case may be, how might one perform this translation as accurately as possible?
To answer that I turn to good old Map 3D. As you may know both AutoCAD Land Desktop and AutoCAD Civil 3D are built on top of AutoCAD Map 3D, so if you have either product, you also have Map 3D. Users of Map 3D naturally know it’s power, whereas I have found many civil engineering professionals nearly forget about the Map menu altogether. While it may seem odd, we’re actually going to start the translation from a blank drawing.