DWG files coming into Revit in wrong place?

[ChuckEdwards]

I'm trying to bring in an Autocad file (a grid drawing) to Revit, no matter what I try, the file comes into the wrong place in Revit. CAD file is attached.

I have marked the required insertion point with a small block in the DWG, layer REVIT BASE POINT. The X and Y values for this in World UCS are 331960000 and 161200000 respectively, and the grid I'm measuring off an orientation of 4.02199022 degrees relative to the X-plane, which I'm using as the "Angle to True North" in Revit.

I have plugged the Y and X figures in Revit Basepoint N/S and E/W values respectively, but then when I insert the DWG as a linked file (Revit plan view set to Project North) using Auto-Origin to Origin, I find the grid comes in rotated at 4.000 degrees from my Project North, and the base point in my CAD file is 17,936mm away.

No matter what I do, the orientation seems to come in at that 4 degrees. I've tried making it -4.02199022 and it comes in the same, even when I change the Revit Project base Point to 45 degrees, it still comes in on 4 degrees? Its as if whatever I do the orientation has been pre-set and cannot be changed.

I also find (for some reason) I have the Revit view set to True North, the orientation comes in with a further rotation on it. Shouldn't it come in the same, regardless of what the orientation is?

Can anyone advise what is happening here to make everything go out of true like this?

I've spent hours trying to figure this out but am no closer to an understanding of what is going wrong. I've tried other project files that use the same base point and have also found the same result, the dwg's just don't come in where they should.

The DWG base point is a UK Ordnance Survey position, adjusting it isn't an option....

NB I'm clear on Autocad UCS's (Autocad user of 16 years) and understand the Revit system too (move the tablecloth, not the table)...

The screenshots show the project basepoint value = the DWG world UCS value, and also the settings in the View (set to use Project North).

[Alfredo_Medina]

The origin of the AutoCAD file is the 0,0,0 of the World Coordinate System. It is not that mark that you placed in the drawing, even if you set that mark as the origin of a custom user coordinate system. That origin, in your file, is more than 33 kilometers (20 miles) from where the grids are drawn. Therefore, Revit cannot use that origin, and, instead, Revit is using the center of the bounding box that encloses all the entities in the .dwg file (the center), and is placing that at the origin of the Revit file.

Before linking your drawing, do not make any changes to your project base point and survey point in Revit. Leave them as they are at their default location, which is the same as Revit's orgin or Internal point. All coordinates at both points should be zero before linking, and ideally, you have not unclipped them or moved them yet at all.

Then, bring the .dwg file as a link, using "center to center" as the method of placement. Then, select the link, and move it, using the intersection of two grid lines in the .dwg file as the base point, and placing that intersection at the place where that intersection should be in relation to your Revit model (your building). Then, rotate the link to match the orientation of the equivalent grids in your model. Use the "Place" button of the Rotate tool, to locate the center of rotation at the intersection of the grids. Then, pick a point at a grid line of the .dwg file, and then a point at the equivalent grid line of the Revit model. Now the two drawings match location and rotation (but not coordinates yet).

Then, in Revit, draw a line or reference plane that begins at the center of that mark that you see in the linked .dwg file. The purpose of drawing that line or reference plane is to have an endpoint that we can use to specify coordinates. Then go to Manage > Coordinates > Specify coordinates at point, and click on the endpoint of that reference (which is at the center of the mark in the .dwg file), and enter the coordinates of this point, and the angle of deviation from project North to true North, based on the information that you already know, as shown in this image:

This will send automatically your Survey Point (the triangle) to exactly the same location of the origin of the .dwg file, which is far away at the lower left corner of the screen, if you zoom out enough. That is fine and that point can stay there. Optionally, if you want to place that point exactly at the mark of the dwg, you do this: find that Survey Point, and click at its center. Then unclip it. Then, you could specify the coordinates if the distance was not greater than the maximum of 20 miles, but since it is greater, you need to manually drag the triangle it to the mark. Once you have the triangle there, exactly, clip it again. Now click on it. You will see that it has exactly the same coordinates as your mark of reference.

Now the two drawings match in location, rotation, North, and North/East coordinates. In this case, this is enough. If you had a civil drawing with the topography you would need to enter also the "z" value, for the correct elevation, or use the other method, which is "adquire" coordinates of the .dwg file.

[ChuckEdwards]

Alfredo, I think you missed the line 'I've been working with Autocad UCS for 16 years so understand it'. I really, really understand it. I understand that the point I put in the Grid file was not the origin (I never said it was), it only represents where in the World UCS of the Grid drawing the same x/y coordinates relate, which is where I expect having set a northing/easting in Revit it should come and drop in on that, with the .dwg point sitting straight over the Revit point.

Still, I've done your workflow in the hope there is something in it.  I've then dropped in the ground floor plan (same origin point as the grid drawing) and yet it has still come in with the same degree of wrongness that I was finding previously. This is as a result not a solution.

I can bring in every drawing I work on the same way, and I can move and rotate them too, but this is still not a solution, and I think not what having a project base point is all about.

[Alfredo_Medina]

Well, all I can say is that the procedure described above works, and the proof is that I am posting here the coordinates of the points in Revit, matching your drawing file, as expected. My impression is that you expect Revit to work in a certain way, based on your AutoCAD experience. I am explaining to you how it works, and I have made your files match in a few steps. If that is not enough, sorry, I pass the ball to someone else who can explain it to you in another way, but that will be just a different explanation of the same procedure.

[ChuckEdwards]

OK, thanks anyway.

[olga]

If you have PBP with coordinates predefined in your Revit project, you should link dwg using Auto - by Share Coordinates option.

Remember as well correct orientation. If you link dwg in the view oriented to Project North, it should be linked with option "Orient to View". If you link your dwg in the view oriented to True North, you should turn off that option.

Your mistake was trying to link dwg Origin to Origin. As Alfredo mentioned, when trying to use Origin to Origin, Revit finds that Autocad origin more than 20 miles away and uses Center to Center. It's confusing that no warning is issued, but such "misbehaviour" is common in Revit in case you have all geometry in dwg laying inside of 20 mile dia. boundary.

Otherwise Alfredo's method would work perfectly for Revit project where coordinates are not defined yet. 

[carmen]

Hi Alfredo,

I'm having quite a bit of difficulty in regards to topography and elevation.

My best attempt at a summary is as follows :

1) i have both the building and topography in the one file

2) i have adjusted the project base point elevation and survey elevation to the correct elevations being 2100mm above sea level

3) for some reason, i have somehow ended up with a topography that is 18 meters above my building, but when i select the internal point of the topo, it says it is at the correct height of 1m...?

4) any ideas on how i can change the topography to the right height so that it matches my building elevation, and the internal points read at the correct height??

Your help would be greatly appreciated!