Here is part of the GEOID12a Model contoured @ 0.1 meters (N) with the outline of Utah over the top.
The 'N' value ranges from about -25.8m at the Southwest Corner of the State, to about -11.6m on top of the Uinta Mountains (~50 SE of Evanston, Wyoming).
Loyal
Did it change much from Geoid09? We still have only a few bench marks. Has the real gravity field been inserted into 12a?
Looks to be fairly steep in a few places (Wasatch Mountains and the slopes of the Unitas).
Leon
I have the same "overlay" for GEOID96, GEOID99, and GEOID03.
There IS a noticeable difference, and when you overlay the GEOID Model(s) over a topographic map of Utah, you can really see how the "shorter" wave length anomalies are more detailed with each NEW model.
Basically...the valleys get “deeper,” the mountains get “higher,” and the gradients in between get “steeper.” At least that is the way I envision it.
Loyal
Okay, I wanna' ask, and if you have time for the dumb questions...
"Model contoured @ 0.1 meters (N) with the outline of Utah over the top."
Does this represent the variation between 12 and 12a, 12 and previous geoid ?
I couldn't understand this with 0.3' contour lines.
R.J.
Sorry for not posting earlier (I no see'm post).
The .1 meter (N) contour interval is just that. One could describe the "map" as a contour map of the GEOID12a "surface."
Loyal
Dave...GEOID12a in Utah
I couldn't figure out how to link to this post, so I just replied to it.
This should give you a "feel" for the variation in the GEOID (surface) in the Utah.
I have never compiled one for Arizona.
Loyal
I just looked at the NGS website concerning GPS on Benchmarks 2014. It looks like Utah needs GPS on a lot of benchmarks to help the GEOID model. If I am reading their chart right 5 cm would be considered great GPS vertical in most parts of Utah.
GEOID12a in Utah TTT
This is why I adjust GPS and Leveling data independently of each other.
Your mileage (and geoid undulations) may vary...
GEOID12a in Utah TTT
Undulations aren't a problem as long as they're accurately modeled. What magnitude of discrepancy do you see between modeled and actual?
GEOID12a in Utah TTT
Jim,
I don't have any HARD numbers handy, it's been a couple of years since I did one of those [type] projects.
Off the top of my head...
Out in the valleys, it's almost (ALMOST) a trivial consideration (usually), but when you push up against the range fronts (or into the foothills), variances in the (roughly) 1-2 tenths in a mile or so may pop up.
GEOID12a is MUCH better than say GEOID93 (or even GEOID99), but there are limitations in the dataset available to the GEOID Team. Once GRAV-D is completed over the Great Basin, I expect to see some rather profound refinements to the Geoid Model in my neck of the woods.
I created these isogram drawings so that I could visualize what was going on in the areas that I generally work in. I have an OLD one for Nevada somewhere, but it's probably an old geoid model.
Loyal
GEOID12a in Utah TTT
Loyal, we discovered a ledge in one of the older models. Never could get a calibration or a model to work for this small property, a community college about 60 acres. The levels were tight but could not get GPS to work very well.
And in the middle there was .4' difference in the model from one side of a street to the other side.
It was an indication that the models were crude at best, not add omething to be relied on.
