WGS84 vs NAD83 - Geolocation

[sgleadleD3EMJ]

Why does the geolocation tab disappear when I try to use UTM with the NAD83 datum instead of the WGS84 datum?

We work in NAD83 epoch 2002 where I live, will using the WGS84 version affect anything? 

[rgilbert_JHA]

Do you use GEOGRAPHICLOCATION or EDITDRAWINGSETTINGS to apply the coordinate system to the drawing? Depending on how you intend to use that setting, it may or may not be a problem - are you just using it to align an aerial? 

[Pointdump]

Hi Shea,
That's unusual. Can you post a drawing where this happens?
Dave

[sgleadleD3EMJ]

See attached short video of the issue. When I already have the aerial turned on then switch to nad83 it loses the geolocation tab but also brings in imagery of some other location that I cannot turn off. Notice the shift in the WGS imagery.

[sgleadleD3EMJ]

Im using the coordinate system for the imagery but I also set a scale factor to be able to view and use my grid coordinates.

[Pointdump]

Shea,
I get same as you in 2023, but 2022 works as expected.
In 2023 I also get "Warning: Cannot save projection code to the drawing." Which might mean a problem with Datum Transformation, NAD83 to CSRS.
You should definitely open a support ticket with Autodesk.
"...I also set a scale factor to be able to view and use my grid coordinates."
You're doing what? Please elaborate a little on that one.
Dave

[Pointdump]

Shea,
Figured it out. Looks like you'll need to add the Canada-wide NTV2_0.GSB file and also the British Columbia specific BC_93_05.GSB file to your "Geospatial Coordinate Systems 14.09" folder. I'm doing that right now and I'll let you know if it works.
Dave

[sgleadleD3EMJ]

Interesting, I will follow up with Autodesk. Thanks for all the help.

Under the transformation tab I enter my combined scale factor (ground to grid) of a centrally located point that I wish to scale about, I can use a shift if I'd like so I don't confuse one with the other. I have a point file format setup to import/export ground and one for grid. And an annotation style to label a point with both, just grid or just ground. So If I have a csv in grid I can bring it in and it will convert it to my projects ground based system, that way I can work and draft with a SF of 1.000 and if I need to go back out in the field I can export a csv (of control or search points for example) in grid if i'm going to use GPS or ground if Im going to use a total station.

One question I have on this front is can civil3d give me an accurate combined scale factor? (CSF = point SF * elevation SF)

It gives me an accurate SF with the geodetic calculator but it doesn't apply a ESF even if I check the "Apply sea level scale factor" box.

Currently I'm stuck using the CSF I get from my post processing or Starnet will give me the CSF of any point I observe but it'd be nice to set my scale point (with its approx CSF) when I'm doing my precalcs and before I even go to site.

[sgleadleD3EMJ]

I have those GSB files now, I just cant seem to find the folder you speak of.

[Pointdump · Accepted solution]

Shea,
Yup, that was it. I thought those GSB files would carry over from year to year, but I guess not. Edit your NAD83_TO_CSRS Geodetic Transformation in MAPCSLIBRARY. Add "NTV2.0.GSB" and "BC_93_05.GSB" to your Grid Data File Interpolation collection. Make sure the BC file is above the Canada-wide file.
The folder you're looking for is C:/Program Data/Autodesk/Geospatial Coordinate Systems 14.09. You'll see that the "Canada" folder only has a ReadMe, but not the GSB. Autodesk doesn't include it because those GSB files are proprietary.
Dave

[Pointdump]

Shea,
You're on your own with the Transformation Tab. I've never gotten it to work. For me it usually trashes Bing Maps and none of the Map functions work. (Like bringing in shapefiles.)
Dave

[Pointdump]

Shea,
"...can civil3d give me an accurate combined scale factor? (CSF = point SF * elevation SF)"
No way I've found in Civil 3D. I've always gotten the Combined from an OPUS Solution. Starnet will give you that too.
Dave

[sgleadleD3EMJ]

Worked like a charm, than you very much.

The Bing imagery is still shifted a few meters, but is closer. Why is that?

What do you do if you want to get a CSF before heading to site or collecting any data? I could pull one from a nearby government control monument but in some cases there aren't any close enough.

[Pointdump]

Bing is never perfect. Neither is Google or ESRI imagery. And none of them match.
If you'd like to shift Bing, there's a method >>>Here<<<.
For Elevation Factor, use r/r+h, where h=ellipsoid height. Online calculator to get radius by latitude >>>Here<<<.
Dave

[Pointdump]

Oh, I just remembered, >>>NCAT<<< will compute Combined Scale Factor.

Dave