@Norman Oklahoma?ÿ Right you are on the geoid height being zero, The ellipsoid and orthometric heights are the same because the geoid height is zero.
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The point being is for a small area the difference between 88 and 29 should be a constant number. This allows the use of the latest Geoid model by either simply occupying the 29 bench mark and using the model, or applying a constant shift number to the 88 number, applying a constant shift number is probably the best way when using a network rover.?ÿ
For a small area the geoid seperation is going to be virtually constant as well. So you could just go without a geoid model at all - especially for dirt work - and just use an offset.?ÿ The trick might be if a remote benchmark was visited.?ÿ ?ÿ
I guess I've been "lucky" to have worked in an area where the geoid models change rather quickly, .5' (or more) per mile isn't at all unusual. That of course works out to a tenth in 1000' and is nothing to dismiss when running elevation control. The change in shift between 88 and 29 however, is negligible in comparison. Once you figure out that number it should be consistent over a few miles.?ÿ
I guess I've been "lucky" to have worked in an area where the geoid models change rather quickly, .5' (or more) per mile isn't at all unusual. That of course works out to a tenth in 1000' and is nothing to dismiss when running elevation control. The change in shift between 88 and 29 however, is negligible in comparison. Once you figure out that number it should be consistent over a few miles.?ÿ
The OP hasn't said anything about the extent of the site. But I'm visualizing something on the order of a city block (200' square hereabouts) because that is what I deal with myself, mostly. If it is as large as a thousand feet of more then, I agree, use of a geoid model may be in order.?ÿ Still, a tenth for just dirt, which the OP assures us is all he is doing, isn't going to be a big deal. Nevertheless my preferred approach here would be to use NAD83(2011), Geoid12B, and localize as and if necessary.?ÿ
The OP hasn't said anything about the extent of the site. But I'm visualizing something on the order of a city block (200' square hereabouts) because that is what I deal with myself, mostly. If it is as large as a thousand feet of more then, I agree, use of a geoid model may be in order.?ÿ Still, a tenth for just dirt, which the OP assures us is all he is doing, isn't going to be a big deal. Nevertheless my preferred approach here would be to use NAD83(2011), Geoid12B, and localize as and if necessary.?ÿ
Calibration, or localization seems to be the only way to go here for the OP. All the stuff about converting from WGS84 to NAD27,,,,,,,that isn't going to work, never seen that work beyond rough mapping coordinates. How could it possibly work?
Treat the control like it's a 10,000, 10,000, 100 grid on a random pin.
I agree completely, like I said before I am NOT a surveyor, I have discovered that I have no business setting my own control. I am very comfortable localizing to existing control and that is the only way that I am going to work moving forward. However, I really appreciate all of the help and knowledge I have gained from this- it has definitely been a learning experience.?ÿ