Creating a Local Ground Coordinate System Automatically Transformed From UTM Grid

[darrenr]

Hi, I need to create a local ground coordinate system that is linked to the original UTM grid projection coordinate system so that it will automatically sync orthos, Infraworks, etc between the two systems. I am trying to muddle through it. The surveyor has provided me with a control monument reference point that will be used to shift to the local coordinate system at 25,000N, 10,000E and scaled by 1.00051527 to get from grid to ground. Then the client has requested that it be rotated 46.76405 degrees as well. From watching a few videos, my understanding is that I need to create a local coord system with the  "MAPCSCREATE" command. I got to the "Modify coordinate system", however I can't find a place to enter the scaling and rotation (see first screen shot below).

Once I am able to get this local coordinate system defined, do I set that as drawing coordinate system in the drawing setting dialogue or leave it as the UTM grid system (see second screenshot below)? Then I set the up the transformation settings I guess. Should this be transforming from Local to UTM grid or vice versa (see third screenshot below)?

Thanks in advance.

[Pointdump]

Hi Darren,
Your Transformation Tab settings look OK, but here's a couple of things to think about. The Transformation Tab is usually only one way. There is no breezy back-n-forth between Grid and Ground. Also, and this is a big deal, there is a disconnect between Civil 3D and Map 3D. The Transformation Tab usually breaks Bing Live Maps and you can't use shapefiles or orthophotos.
The next step is to use a custom projection. (I've never seen anyone use a custom projection and the transformation tab together in the same drawing.) Creating a custom transverse mercator projection is no biggie, but the 46.76405 degree rotation would require using an oblique mercator projection. I don't know if that's a good way to go. If a rotation is desired, might be better to use DVIEW >> TWIST in your drawing.
If you want it all, rotation and breezy back-n-forth between grid and ground, consider a custom affine projection. Good video >>>Here<<<, keeping in mind that the rotation parameter can be added.
Dave

[_Hathaway]

That all sounds like a lot of work and potentially alot of trouble.  For instance, the moment you move the surveyors data in any sense they have no responsibility for your downstream issues.  The data supplied by the surveyor should stay in it's delivered form or updated by the surveyor and resubmitted. 

[darrenr]

Thanks  for your response Dave. I thought I saw a video where someone was working in a local coordinate system but was able to reference orthophotos from their original coordinate system and it automatically made the transformation.  Yes it was a specific request by the client and this is something they have done in the past. It would be amazing if Autodesk could make this happen in the future with an auto tranform back and forth and much easier to set up. Ultimately everything has to be transformed back and added to GIS. I might be able to talk them out of the rotation, however, a bunch of work has already been completed. Thanks for the videos, had a quick look but will have to review again to see if I can make sense of it.

[darrenr]

Yes it is a bunch of work but a requirement from the client. They had the surveyor provide the survey in both the original UTM grid and the transformed local ground system so I did not have to make the transformation of the survey itself. I'm sure they would also like to know how to do this auto transformation in Civil 3D (I think they use other software for the conversion of points and then manually transform linework). There is other info, like orthos, LiDAR surveys, GIS data that needs to be converted and added to the Civil 3D file which I have been doing manually. Thanks.

[Pointdump]

Darren,
If you can post one of your drawings I'll demonstrate how to create a custom affine projection.
Dave

[ChicagoLooper]

I agree with @Pointdump 

Create then use a custom coordinate system using the 'original' UTM-Zone as a starting point. You can name the newly created CS UTM-Zone_Ground. When you swtich from UTM-Zone_Ground to Original your coordinates (including Lat/Longs) will still hold true, assuming of course, you created the new Ground system correctly.  

[darrenr]

Thanks Dave, I have blocked out control monument A which is the reference for the transformation as well as a second monument B and a surveyed feature line to simplify it. Drawing coordinates are NAD83 (CSRS) UTM Zone 10N. Vertical  Datum is CGVD 28 HTv2.0. The scale factor from grid to ground is 1.00051527 about monument A. The rotation is 46.76407 degrees. The second drawing shows the same drawing in local ground system.

I have been watching some videos on how Autodesk and ESRI are uniting geographic information system (GIS) and building information modeling (BIM) technology which is pretty cool. I don' think what we are doing is the most efficient way to manage/work with drawings to be used between different platforms and with multiple team members. What is the best/proper way to set up a drawing in a local coordinate system so that it is easily managed between Civil 3D, Infraworks, BIM, GIS, etc. I see all these massive BIM projects and wonder how they make it easy to collaborate between ground and grid GIS data. Thanks again!

[Pointdump]

Darren,
I got pretty close. For an Affine Transformation you need at least 3 points. I had to create a 3rd point out of thin air, and I probably got that wrong. Also, for your grid coordinate system I used EPSG:3157 and I haven't installed the BC grid files, so my transformation from CSRS to NAD83 to WGS84 probably was off. And I kept the standard "0.9996" scale factor of UTM10N. In retrospect I should have set the central meridian on MonA and used your combined scale factor. I'll play with it tonight.
I'm attaching a drawing with the custom affine coordinate system and the Excel file I used to calculate the affine parameters. I learned this from Egor Grebenyuk @georg.grebenyuk. Sadly, I can't find his excellent white paper that used to be in the Autodesk Knowledge Network.
For transforming from grid to ground you can use the Attach/Query method on linework, aerial photos, and shapefiles. For Civil 3D objects, like COGO points and surfaces, you'll need to use the Coordinate Transformation Tool in the Toolbox Tab under Miscellaneous Utilities.
Dave

[Pointdump]

Darren,
I got a lot closer by tweaking a few parameters and adding the BC Grid Shift files, but not good enough. I've seen Bing Live Maps off by more than this, especially in Canada. That's not really worrisome. What is worrisome is wrong coordinates on the lower status bar and the ViewCube should be rotated 46.76407 degrees. So I've got to say I don't recommend this way. I've had good success before with custom affine projections. I'll do more testing to see if I missed something.
Dave

[darrenr]

Wow! Thanks for your time and effort Dave. Much appreciated. This seems a lot more difficult then what I was hoping. I thought it would be as simple as inputting the projected coord system and the local conversion and it would scale, move and rotate it automatically. I have no idea what those custom setting are that you are playing with. I think I will just continue converting manually for now. That polygon I included is the top of the structure which is sticking way out of the ground so I don't think it will line up propertly. I always find that tops of buildings etc do not line up very well with the orthos because they are not necessarily takin directly above the objects (I think).  

[Pointdump]

Darren,
It was killing me so I spent some time and got it working. I learned a few things along the way. To calculate the parameters for an affine projection you need at least 3 tie points. My first attempt to Rube Golberg a 3rd point wasn't good and so I tried to play with some of the parameters that I shouldn't have. The A0,A1,A2,B0,B1,B2 parameters do all the work. Everything else should be the source EPSG:3157 parameters. My second calculation of a 3rd point was much better.
Another fine-tune is to add the British Columbia GSB grid shift file to MAPCSLIBRARY. Not mentioned in >>>This support article<<< is that each province has at least one GSB file that supercedes the national GSB file. It should be placed above the ".\Canada\NTV2_0.GSB" file. Without doing that I've seen Bing Live Maps disagree with linework as much as 70 meters.
The >>>Coordinates Transformation Tool<<< will allow you a breezy back-n-forth between grid and ground.
Dave

[darrenr]

Incredible Dave! Thank you again. I'm going through this in baby steps as it's all new to me. I had to download and install the Transformation extension for the Toolbox. I then set my original drawing "Units and Zone" to "NAD83(CSRS) / UTM zone 10N". Then created the local coordinate system using the parameters you provided (see screenshots below). When I executed the "Coordinate System Transformation" command, it transformed it but not to the correct local coord system. Mon A is at E24761.332, N11072.594 instead of E10000, N25000. I haven't figured out how to add the British Columbia GSB grid shift per your recommendation so will try to figure that out as well. I would like to understand further how you came up with those affine matrix calcs in the Excel spreadsheet so will spend some time trying to reverse engineer them too. Once again, thanks for getting me on the correct path here.

[Pointdump · Accepted solution]

Darren,
Whenever you create a custom coordinate system you need to exit the program and start it back up. (A subtle thing that has tripped me up before.)
I tried out the Coordinate Transformation Tool just now and it works good with one caveat. After the transformation, C3D doesn't automatically assign the CS. You'll need to use MAPCSASSIGN before you can use Bing Live Maps.
Dave

[Pointdump]

That spreadsheet uses some matrix algebra. Excel does a quicker job than manually solving. I also show the Inverse Matrix and Identity Matrix, just to check my work.
Another way, a bit easier, to get the 6 parameters is to use QGIS. Workflow >>>Here<<<.
Dave

[Pointdump]

Edit your "NAD83_to_CSRS" Geodetic Transformation to add the BC Province GSB file. Civil 3D starts at the top of the list, so you can add other Provinces and it will choose the first one that applies to your area.
You'll put the BC GSB file here:
Program Data\Autodesk\Geospatial Coordinate Systems 14.10
(14.10 is C3D 2024)
You can get all the GSB files for Canada >>>Here<<<. (You'll need to create an account, but it's free.)

Dave

[darrenr]

It Worked! I would have never figured this out without your help Dave. I noticed when I did the transformation from UTM to Local, there was a very small error (See screenshot below). Every time I do the transformation back and forth, it adds to this error.

Now that I got this working, my next step is to turn on the geomaps in the local coord system and have it do the transform automatically per the video you sent. It's not working at the moment. When I assign the coords to my local affine system, it tells me "no geographic location defined" when using "geomaps" command.  I also thought if I used the "mapiinsert" while in the local affine system to bring in my ortho files, it would automatically convert them from the grid coords to local but it doesn't. I'm going to try and set up an Infraworks project in the local system next and see if it automatically converts objects imported in grid coords to local. 

[Pointdump]

Darren,
"Every time I do the transformation back and forth, it adds to this error."
Yup, and the only thing that might help is to bump up your precision to the max.
I was using Bing Live Maps in the custom projection, but it was slow and came in with small tiles.
As for your orthos, MAPIINSERT won't work. You'll need to use Raster Tools IINSERT or MAPCONNECT.
Dave