Situation with shifting coordinate systems

[Sahay_R]

Just received this from a consultant - 

"I was wondering if you could help me get some control points inserted into the model correctly.   I received the GPS coordinates from XXXX and those points imported perfectly into the model, however those points are too far away from the building to be useful to us.  I received another set of coordinates from YYYY who is working for ZZZZ.  They are working of a local coordinated system developed from a best fit scenario to some existing benchmarks. 

My problem is that our Project Base point (0,0) at column line A-3 is at their point 204 (5116.466, 4292.190)  I had thought that it would be no issue move our PBP so that the two points aligned and we could all work on the same coordinates, however much frustration I have realized that this is not the case.  Our Trimble points can be imported either relative to the shared coordinates or not.  I had assumed that ‘not relative to shared coordinates’ would mean ‘relative to project base point’ but it would appear that it really means ‘relative to project origin.’  No matter how I move things around I cannot get A-3 to be the same as 204.

The only two options I can come up with right now are:

1. I could import the points using shared coordinates and discard the GPS coordinates, but I would rather not discard information
2. I could relocate all the points from S-D and reimport into Revit, but that would mean that there would be two active coordinate systems on the site.

Either of these solutions could work, and may or may not have further implications/cause confusion down the road.

I would really like to be able to relocate the origin point (AKA the mysterious third coordinate system that may or may not exist according to internet experts) but I have no idea how to do that."

Has any of you dealt with this kind of a situation before? I did find a set of detailed and informative responses in this thread   -

https://forums.autodesk.com/t5/revit-architecture-forum/revit-coordinate-system-and-project-site-set...

but what I am looking for is an idiot-proof workflow that I can suggest to the concerned consultant as well as refer to for our projects in the future.

[barthbradley]

@Sahay_R: I'm a little confused, but it sounds like the consultant just wants to Relocate his project. No? 

[Sahay_R]

@barthbradley Welcome to the confused club. That is my thought exactly. But since this is a first for us, I would really really like to make sure.

[barthbradley]

@Sahay_R: Well, I think a lot of confusion would be cleared up by asking the contractor what he means exactly by "control points".  

[SteveKStafford]

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@rsahayUZMK9 wrote:

Just received this from a consultant - 

My problem is that our Project Base point (0,0) at column line A-3 is at their point 204 (5116.466, 4292.190).

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You/they want the intersection of grids A/3 to report: 5116.466,4292.190 for the Survey Coordinate System? If yes, then Specify Coordinates at Point (SCap) will do that. That would suggest to me that the survey would be out of position relative to this location too.

There is no way to change the coordinate system relative to the Internal Origin without moving the model. We can move the PBP unclipped but that only alters the models relative position with regard to the survey coordinate system (Relocate Project does the same thing). If a specific grid intersection must report 0,0 when export to DWG using Project Coordinates, then the model itself has to be moved so that intersection is at the internal origin.

[SteveKStafford]

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@Anonymous wrote:

@Sahay_R: Well, I think a lot of confusion would be cleared up by asking the contractor what he means exactly by "control points".  

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Seems unnecessary, to me, to even use these control points since he wrote they came in at the correct location. Coordinates are just values for any given point location within a cartesian grid system. If the coordinate systems are matched then they can put control points anywhere they like. The goal is to provide a meaningful reference for excavation, form work etc. No?

[barthbradley · Accepted solution]

You're kinda of making my "point", @SteveKStafford. The only data associated to a "point" is its relative position to something. I imagine that "something" is a geodetic marker. No?

[SteveKStafford · Accepted solution]

I'm agreeing with you. The so called control points came in at the correct location so, in a sense...nothing needs to be done. Any point they choose to interrogate via a Spot Coordinate annotation for example will report the correct coordinates relative to whatever those control points are referencing...which must be the survey's coordinate system...if they landed at the correct location.

[barthbradley]

Now the question is: which "points" does the contractor use? GPS or Trimble? Sounds like each are based on a different geodetic markers. 

[Anonymous]

Good Afternoon, 

As the aforementioned contractor, I appreciate all of the responses to this question.

The points made about everything basically importing correctly, is correct.  My confusion comes largely from trying to keep the coordinate from YYYY the same as the points we shoot, which originate from the project base point.

The issue is that when we collect the control points set by YYYY and import them back into the model, Trimble only has a checkbox for "via shared coordinates"  I had assumed that unchecked would mean 'via project coordinates' but instead it means 'via origin to origin.'  All of these option do actually import correctly, and all these coordinate systems would report the same same spot as long as the origin is still the project base point, and as long as YYYY didn't arbitrarily move 0,0,0.... As they do to keep all of their survey points in the +/+ quadrant of the NEZ coordinate grid.  (I was told this is best practice to avoid dropping "-" in tables)

My problem now is that I have a 1 point that has 2 different sets of coordinates.   3 if you count the GPS points.  The main question is one of clarity.  I would rather not have extra coordinate numbering on the job site.  It may cause confusion, it may not, I don't know.  I don't want to discard the GPS points from XXXX as it is a rather large site and those points could be useful so that means I can't relocate the project.  I can't move the project base point, because trimble doesn't import relative to it.  I can't move the origin because, well, Revit.  I can't move the building without wreaking havoc on the model.

I chose to discard YYYY coordinate numbers, shifted the points in AutoCAD and reimported.

The only two solutions I see are 

1) Trimble adds an option to import via Project Base Point

2) Revit allows manipulation of the origin point.

Option 1 sounds great.  Option two sounds like opening up many more problems.