I don't use site calibrations.?ÿ If I need to start from nothing I'd set it up in a SPC and the HERE KEY and modify later.
In my view a site calibration is a method to set up a LDP using existing points/coordinates.?ÿ If what's on the ground is tight then the result will be good.?ÿ If the ground points are not so good then the site calibration will not be very good.?ÿ If you mess anything up it WILL BE BAD.
GPS will give you very good real vectors.?ÿ All the projections/calibration/etc is just a way to look at it.?ÿ I takes the points and converts them into something like a plane survey (flat earth) easy to understand.?ÿ Once you grasp the concept and learn the ropes you'll probably not use site calibrations that much.?ÿ If all your underlying coordinate data in in ECEF XYZ (whether you realize it or not) changing how you view it in flat earth terms is as easy has changing clothes.
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If you use site calibrations look in the file and see what "Projection" it is using.?ÿ That is the "LDP/site calibration" that the site calibration set up for you.