Discrepancy in lat/long location of Revit Survey Point and AutoCAD Position Mark

[snhaabi]

Hello all,

I have a Civil survey CAD file of my site that has Geolocation data. I strip all its geometry and leave just a 'Point' object where I want Revit's internal origin to lie with respect to the survey when I link it in later. I first linked in the survey file containing nothing but the point object (origin to origin). And Acquired Coordinates from this linked CAD file. Now, when I link in the original survey file (Auto - Shared coordinates) everything seems to line up perfectly. Exporting a .dwg from this Revit model to import into that original CAD survey works exactly as required—with all objects in alignment. 

Now here's the problem: The Revit 'Location' (in Location Weather and Site) defines location by getting it from the Survey Point. And lists the GIS coordinate system, and its lat/long values. These lat/long values don't match the lat/long values described by a position marker placed at the same location as Revit's survey point in the geo-referenced AutoCAD drawing. The .dwg file uses the same GIS coordinate system. I don't know if I should be concerned about the discrepancy since the values match up until three decimal degrees. 

See attached screenshot for reference. I've blurred out parts of the snip since this is a confidential project. 

Does anyone know if this is a Revit limitation? Or if there's a way to ensure that Revit's Location information matches the linked AutoCAD file exactly?

[joe_keogh]

Hi @snhaabi 

I can't say that I have considered this before.  As in that the Location Weather and Site is an accurated representation of GIS coordinates.

If you select the Project Origin, unpin it from the project, right click and select Move to Startup Location, does the Project origin remain in the same position?

[snhaabi]

Hi @joe_keogh 

Yes, I tried doing that to check. Right-clicked on the Project Base Point and hit 'Move to Startup Location'. It remains in the same position with the same N/S, E/W values as before. The Location Weather and Site is also unchanged. 

[joe_keogh]

And when selected, the Projet Origin reports the same Lat/Long as the CAD survey file?

[barthbradley]

I'm not following. There is no correlation between Survey Point and Project Location. Also, the Survey Point coordinates are not Latitude and Longitude.   

[snhaabi]

Where does the Project Base Point report lat/long values in Revit? The only Identity data connected with it are the N/S and E/W values. And these are slightly different from the Position X, Position Y values in the CAD drawing. See attached snip. Granted that the difference is only of the order of 0.0001 feet, but there is some discrepancy however minor. 

[snhaabi]

Hi @barthbradley,

I think one can define the location using Survey Point if the coordinates are acquired from a geo-referenced link. See snip attached. And I agree with you—Revit's Project Base Point and Survey Point coordinates are not latitude/longitude. 

[barthbradley]

---

@snhaabi wrote:

Where does the Project Base Point report lat/long values in Revit?

---

Geographic Location.  

[FAIR59]

The Revit UserInterface using the propertiespalet has a quirky way of dealing with input. First it rounds the input conform the Project Units and uses that (rounded) value to store in the database. 

It might be that Acquire  Coordinates uses the same method.

Solution:

• set the Project Units for Length and Angle to the maximal number of decimal digits.
• Aquire Coordinates
• reset the Project Units

 

[ToanDN]

It could be this:

http://www.kylesconverter.com/length/feet-to-feet-(u.s.-survey)

[joe_keogh]

My Apologies I meant Northing and Easting.

[snhaabi]

Thank you for the suggestion, @FAIR59. I thought it might be to do with unit accuracy too. Since this project is set in the US and uses the Imperial units. 

I followed your advice and started a clean new file with units set to that extremely high degree of accuracy. Linked in the geo-referenced CAD drawing and hit 'Acquire Coordinates'. Opened the Location Weather and Site window only to find that the latitude and longitude values matched the same as in the other file with units set to feet-inches. No luck there. 

Then, just to test, I changed the units in the geo-referenced survey file as well to millimeters. And angles to decimal degrees. Linking this metric unit DWG into Revit and using it to acquire coordinates resulted in the Revit being unable to read latitude/longitude values from the DWG. Those fields showed up as blank. See snip attached. 

[snhaabi]

Hi @ToanDN : I looked into the link you sent me and compared the readings I was seeing for dimensions in feet on AutoCAD vs Revit. And the difference in the dimension values between software is much smaller than the difference in unit values between those two measuring systems. See attached snip of values seen when compared. 

This doesn't seem to be the reason either. 

[FAIR59]

Revit stores the lat/long values as radians. Change the units for angles to radians (highest degree of accuracy) and try again. 

[indiana_j0nes]

I am not sure if this can help.

It seems like a lost in translation issue.

Or is a non-adressed revit limitation.

Have you tried it with earlier versions?

Or a new template? Instead of your office template, so we can rule out the issue to be specific to the project settings?

https://up.autodesk.com/2019/RVT/C3D_Revit_SharedReferencePoint2019.htm

Keep us posted. It sucks to be lingering with a issue for more than two days.

Cheers.

[hsRASX8]

I think this is a bug. Revit displays the wrong Latitude/Longditude when "Define Location by" is set to "Get Location From Survey Point". The project's latitude is 59,91 degrees north, but Revit displays 49,00 degrees, about 10,9 degrees off. The Longditude is 0,3 degrees off.

My coordinaes are correct (from civil 3D). The Survey Point is located in 0,0,0 in this coordinate system. The Project Base Point displays correct coordinates.

This probably means that the sun diagrams will be incorrect. Please fix this bug, Autodesk.