Geo-referencing and KML
TPC Connection members are already using the new KML tools in TPC Desktop 2015 R1 and we’re hearing about how fun it is to use. That’s great – Just what we wanted to hear. They are discovering what a great tool this can be for reconnaissance and planning.
But what about accuracy when I export my survey as a KML? What if things don’t line up exactly?
Here’s the key. Google Earth stitches photos together to create a geodetic photo background. That means the survey you export as KML needs to be geodetic also. In other words, the survey you export as a KML must have the appropriate Coordinate Reference System (CRS) and should use geodetic positions that match physical positions on the ground. Yes, for small surveys, you can still do an orthogonal, grid survey starting at a known geodetic position but the further you move away from that position, the more error you will see between your survey positions and Google Earth’s position. Switch to a geodetic survey with true bearings and ground distance and you will get a better fit with Google Earth.
I also want to remind you that inside TPC’s Drawing View, you can geo-reference a photo with four clicks – two on your survey and those same two points on the photo. Now the photo will be scaled, rotated and translated to your survey and will keep that relationship even as you re-scale and re-position your survey in the drawing.
Mark Lull, Technical Support Manager