Map 3D Projection Rounding – It’s Just Cosmetic

This is a reprint from an earlier blog (May 25, 2011) that is no longer available online.

Last week, I was attending Arizona Professional Land Surveyors Annual Conference, Tom Homan, a GIS Coordinator for Gila County did a great workshop on working with AutoCAD Map. While he was preparing for his presentation, he was working with AutoCAD Map 2012, and ran across a potential problem. He found what looks like a problem with the coordinate projection used in the Arizona State Plane projections. While looking at the details for the projections, he noticed the Scale Factor was showing a 1.000000 rather than the expected 0.9999. That may not sound like much, but that’s 1 in 10,000 units, or a foot across a little less than two miles. This is a pretty big difference across a large are, such as an Arizona County (the counties in AZ are typically larger than those of most states). Now, Gila County, AZ is a mountainous area with a lot of vertical change which can really cause havoc with projections. To deal with this, they use some custom Low Distortion Projections. He also found a similar problem when creating these custom projections. After saving, the projection file was rounding up to 1.000000 as well.

So after digging a little bit, and reviewing the projection definition dictionary, the correct scale factor was built into the files. I also created some data, did some reprojections, and exported out to a shape file to see how the projection file (PRJ) turned out, and sure enough, it was creating the correct scale factor. It looked like it was a cosmetic issue with the dialog box form. So, after creating a support case with Autodesk, Nathan Moore validated the issue as a form display parameter rather than a functional problem with the dictionaries. The issue is also present in Civil 3D 2012.
So, the good news is the projection tools in Map 3D still work great, and with the new tools much easier to work with.