Project Coordinates, Shared Coordinates, and the new Survey Point

[Steve_Stafford]

Yes

Revit is concerned about geometry that spans large distances (20 miles is the current "limit"), not the coordinate values themselves. If your building is modeled near the Revit project origin you can still define what real world coordinate values a specific location should have, such as a benchmark, grid intersection or building corner etc.

If your survey file has geometry near the origin as well as the site contours and property information very far from the origin, that is the condition Revit is concerned about. You can leave the geometry where it is, the relevant stuff, but you should strip out the information that is near origin.

[aargumaniz]

Sorry Steve but I must contradict. I know that we've had this discussion before where, as you mentioned, you can have large coordinates as long as your geometry is not greater that a 20 mile cube, is it drawn by the origin point and no linked model or CAD file is beyond the limit. I have 16 projects set up exactly as you mentioned and every single one has graphic issues. I have tried moving the survey point back to the origin point without modifying my coordinates and I still have graphic problems.

The problem I am having, or was since I removed shared coordinates, is that my section cuts were not displaying the correct information. Sometimes it would show items that were behind the section cut. This is very dangerous because we are use to Revit automatically creating these sections that we fail to verify if the information is correct. After many hours of trying to figure out what the problem was, I sent my file to Autodesk and they confirmed that it was the shared coordinates being larger than the 20 mile limit regarless if my geometry didn't exceed this constraint. (This is an example of a survey point I had to match E/W: 6457476.2445, N/S: 1845267.3191)

Someone asked a question a few post back as why use shared coordinates. I also thought that way until I had to work on a project where multiple software platforms were being used, Autodesk and Bently, and it was critical that the model align to the exact survey point when exported. This caused issues because the survey/shared coordinate point was large. My work around involved using Revit, AutoCAD and Microstation to ensure the coordinates were accurate. Now if this wasn't enough, when the files are handed over to the Client the Revit files MUST have shared coordinates; even though I know that the graphics will not be correct.

I don't understand why Revit has a 20 mile limitation, when other softwares handle true coordinates without difficulty.

[Steve_Stafford]

My information comes from people inside the organization too. I've worked with files that have similarly large coordinate values without the issue you describe. The developer I've chatted with said that all cad software deals with this distance issue. 2D representation is less affected by the truncation that occurs with very large distances

It's all math under the hood. When the design cube is small enough the variations are too small to notice, they get worse and worse as the distances increases. The limit is imposed to try to restrict the inaccuracies that occurs. 3D solids and vectors multiply the complexity of the problem. If he (my contact) is to be believed, all the other software out there deals with it, the others hide it from us "better". Hidden doesn't mean it isn't there, they are just "faking" the results so it doesnt "bother" us.

Obviously I can't disprove your results. All I can say is that the concept is intended to work as I described. If it fails to then perhaps there are issues within the code at present that are in conflict with the intended behavior, a bug in other words.

[aargumaniz]

Very interesting. I guess that I'm going to have to pick your brain further to understand exactly what you are doing to achieve the large coordinates without the geometry errors. I'll have to chat with you at the RCT in Georgia.

Aracely

[Steve_Stafford]

Sure, look forward to chatting with you there. Doing a class on shared coordinates too

Another aspect of this to consider is rotation. If the sections you were having issues with cut through a building that is rotated very precisely (not "clean" numbers)...like 18.0000051 degress... this could possible contribute to the issue. The coordinate size could factor in somehow too.

Just to reiterate for another reader who stumbles on to this, I recommend a separate building and site file. The site coordinates are defined in the site file with the linked survey. The building file is built orthogonally in its own file (easy to put on paper). The building file is linked to the site and moved to where it needs to go. Publishing the coordinates to the building file synchronize the two files shared coordinates.

Technically nothing changes in the building file except the "understanding" of the true coordinates. I don't really have to put the building file in the site file to do this. All I need to know is a valid coordinate value for a known location in/on or around the building. I can use Specify Coordinates at Point to define the shared coordinates in the building file if I'm armed with that info. I unclip the Survey Point so that I can move it to this location in the building file. This also prevents it from showing up at the survey 0,0,0 origin, which makes it hard to see the building when you use Zoom to Fit.

[aargumaniz]

As a matter of fact I have already enrolled in your class. Now the rotation angle does play a part in one of the projects, or maybe more. Do you think that the rotation from True North to project North can also play a part in the issue? All of the files have a rotation from True North to project North and they are not a nice whole number but more like this 41° 19' 39" west.

Both the site file and the building file are rotated from True North to project North so that we can place it on our sheets. I wonder if this has anything to do with the graphics issue? Something else I have noticed while working with shared coordinates is that there are occasions when I can't select a linked file. This linked file has shared coordinates which I have published from the building file. Perhaps I should have published the coordinates from the site file instead.


Aracely

[Steve_Stafford]

From your various descriptions in this thread it sounds to me like shared coordinates are getting blamed because it is the easy culprit, "Yep there are large coordinates, guilty!"

Obviously the only way to find out for sure would be a much closer look.

[gbrowne]

Steve, thanks for the answer. I think part of the problem was a decimal place error... I have stopped work on that project awaiting the go-ahead from the client. I'll keep you posted.

[cmalenki115420]

So Jeff, are we talking about the startup basepoint, or any location that the basepoint is moved to? So if we move the Project Base Point a mile away from the startup location, isn't that going to be a problem? I assume that the caveat about model positioning is with respect to the startup/original location of Project Coordinates...

Hello everyone. I been following conversations and would like to comment. I presume it would be better to keep the project at the startup basepoint or original location and work outwards within the project coordinates. I consider that it does not really matter where the project site is erected within the 2mile radius of the original location. However changing of project location may have some effect on the existance of the original basepoint and it may be appropriate the project to build up on the original basepoint and outwards. Just an opinion if the Project is what I assume.

[tarrah]

This was SUPER helpful! Thank you Wes!