I had to write this up after the struggle I went through.
I just spent several days working through a means to export GPS data from Google Earth, derive elevation numbers from those points, then convert them to a Cartesian map system to import into SketchUp to recreate 3D topography of a site. A very big chunk of time was spent learning new terms and ideas that I'm barely familiar with.
I tried GRASS, which was a total failure because it was a crappy UI front for GDAL which is a command line interface. What's the point of building a crappy UI that barely hides the CLI? No, really, the CLI interface is in a window that is below the GRASS UI window. I mean that's just sad.
Fortunately, GRASS is really just a portion of Q-GIS which is something akin (not quite as good) to ArcGIS but open source. That didn't work out so well either, as the half-dozen methods did not work. I mean, sure, there's probably a way to work through it all, but after getting the same errors over two dozen times, and without any means to discern the source of the error, it's a dead end.
One of the methods I'd been working through, involved importing KMLs into a free website, GPSVisualizer.com, to find elevations -- Google Earth GPS is 2D points. Eventually -- and by eventually I mean, an hour ago -- I realized that this site could do file conversions, including to UTM, in a single step.
So, you'd think there was a SketchUp plugin to make this whole thing a turnkey operation. There isn't. There's this guy -- CMD -- whose extensions sort of work. I say sort of because you have to precisely follow the requirements of the CSV file in order for it to work. Even then, when I tried using UTM numbers it failed. The reason why it failed is that UTM is generally measured in meters, even if elevation is separately provided in feet, and CMD's extensions were always expecting feet in the easting and northing measurements from UTM.
To simplify UTM data, I removed the header numbers (these identify the nearest latitude and longitudinal angles) from the easting and northing, then converted them from meters to feet, so that everything could be plotted simply into Cartesian. I imported the CSV into SketchUp using CMD's Total Station Point Importer, and that's when I immediately recognized that the Google Earth topography wasn't any different than that from Digital Globe's.
You see, SketchUp replaced Google Earth from its 3D topography for Digital Globe, and from visual inspection it seemed that GE had more accurate 3D topography. Rather than having to modify the terrain based on guessing, I figured I might save myself a ton of time by just figuring out how to use Google Earth's topography.
Oh yeah, and if it had worked out and Google Earth's topography had been vastly more accurate, I was prepared to write out an entire post with full instructions for others to follow. After day 5, this became the saving grace -- that I could find a simplified method for others to use, then show them how to use it. All for naught.
Thus, a week of fighting to find a solution to a discrepancy which did not exist. Now, if any of this sounds more like gobbledygook you can imagine my smile earlier today when I reached this conclusion.
D'oh!
NOTE: A special shout-out to Blogger for a bug that posted an earlier, uncompleted post, from an earlier automatic save. Coming back to find that they've screwed it up royally...precious.
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