Point Cloud Import from Recap not Lining Up in Revit

[aaron.bortz]

I was curious if anyone else has had this problem or found a solution:

• I generate a point cloud using drone images with Pix4D, ordinated to the local coordinate system using GCPs in an .las format.
• Bring it in to Recap and the coordinate system is exactly the same for all points. Everything checks out.
• Export as .rcs for Revit.
• Import the .rcs version into Revit by shared coordinates and it comes in offset from where it should be. Almost exactly the same offset regardless of project.

Any ideas as to why this is happening?

[barthbradley]

Insert the Point Cloud into another Project and Link that Project with the PC into your Project. Set up Shared Coordinates between the two.  

[aaron.bortz]

Thanks for the suggestion. Not quite sure of the workflow on that.  Seems like a roundabout way of manually lining it up.

I was hoping for an accurate coordinate-coordinate import. We spend a lot of effort with GCPs ordinating the data in Pix4D.

The coordinates for any object are identical in Recap and its counterpart in Revit. It's when I import the point cloud into Revit that there is a disparity.

[barthbradley]

Well, if you are linking Point Cloud via Shared Coordinates, then the Point Cloud origin in landing at the Project's Survey Point origin.  

[ToanDN]

How did you establish the Shared Coordinates in the Revit model in the first place?

[barthbradley]

Point Clouds - From georeferenced to local Revit coordinates - Modelical

[aaron.bortz]

Placed the Civil CAD center to center and inherited the coordinate system from it.

In theory, they should be on the exact northing/easting coordinate system. NC83F in my case.  

[ToanDN]

---

@aaron.bortz wrote:

Placed the Civil CAD center to center and inherited the coordinate system from it.

In theory, they should be on the exact northing/easting coordinate system. NC83F in my case.  

---

So that checked out.  How did you align the scanned pointcloud model with the Civil CAD drawing?

[aaron.bortz]

@ToanDN 

For aerial scans we use a drone with Pix4D software. Within that software, we use ground control points to ordinate it to the real-world coordinate system. When I bring that aligned scan into Recap, which is set to the same NC83F coordinate system, hovering the cursor over any point displays the correct coordinate for that point. It's after I export it from Recap and import it into Revit that I see the displacement.

I think it may be due to what @barthbradley is getting at- due to Revit truncating large numbers. When I "reverse engineer" it and change the origin point in Recap to match the coordinates of the origin point in Revit, including the xy rotation to match the angle to True North, the point cloud pops in fine when imported 'Origin to Internal Origin'.

I'm not sure this is the issue and 'By Shared Coordinates' would be my preference in alignment. So I'm still open to suggestions.

[ToanDN]

---

@aaron.bortz wrote:

@ToanDN 

For aerial scans we use a drone with Pix4D software. Within that software, we use ground control points to ordinate it to the real-world coordinate system. When I bring that aligned scan into Recap, which is set to the same NC83F coordinate system, hovering the cursor over any point displays the correct coordinate for that point. It's after I export it from Recap and import it into Revit that I see the displacement.

I think it may be due to what @barthbradley is getting at- due to Revit truncating large numbers. When I "reverse engineer" it and change the origin point in Recap to match the coordinates of the origin point in Revit, including the xy rotation to match the angle to True North, the point cloud pops in fine when imported 'Origin to Internal Origin'.

I'm not sure this is the issue and 'By Shared Coordinates' would be my preference in alignment. So I'm still open to suggestions.

---

There are 3 components that need to align: a Point Cloud, a Civil CAD file, and a Revit model.

- The alignment between the Civil CAD file and the Revit model is via the shared coordinates established in the Civil CAD file and acquired by the Revit model

- The alignment between the Point Cloud and the Revit model via (supposedly) the same shared coordinates

- Have you brought the Point Cloud file into the Civil CAD file (AutoCAD or Civil 3D) and see if they align?

[barthbradley]

Betcha my link suggestion is looking pretty good about right now; huh? 😉

[aaron.bortz]

@barthbradley 

No. Still looks like an overly-complicated solution to a simple problem. I'm more interested in the root of the problem. Thanks for the suggestion though. 

[aaron.bortz]

@ToanDN 

I tried bringing it in to the civil CAD in Civil 3D set to the same coordinate system and got the exact same offset.

The exact same point in Recap reports a different (correct) set of coordinates than Revit and Civil 3D. Truncating decimals is one thing but the discrepancy here is feet. 

[barthbradley]

---

@aaron.bortz wrote:

@barthbradley 

No. Still looks like an overly-complicated solution to a simple problem. I'm more interested in the root of the problem. Thanks for the suggestion though. 

---

The root of the problem is the Geographic Marker and Grid Coordinate System and the extraordinary extents – well beyond Revit’s 20 mi (33 km) limit. If you can figure out a "solution", then please, do share.  It’s not just about Point Clouds.  It affects Autodesk Point Layout too.   

[ToanDN]

---

@aaron.bortz wrote:

@ToanDN 

I tried bringing it in to the civil CAD in Civil 3D set to the same coordinate system and got the exact same offset.

The exact same point in Recap reports a different (correct) set of coordinates than Revit and Civil 3D. Truncating decimals is one thing but the discrepancy here is feet. 

---

There you go. So it is not a Revit's problem but the scanner's or Civil3D's.  But you said earlier you getting the same offset regardless of projects so I am more inclined to the scanner.  Have you calibrated it?

[aaron.bortz]

@ToanDN 

We're using a drone and the data is oriented using GCP's.

I wouldn't say that's the problem because the point cloud coordinates go from Pix4D to Recap flawlessly-coordinates line up perfectly. It's the Recap to Revit step where they get off.

[aaron.bortz]

@barthbradley 

The simplest solution I've found so far is to update the origin in Recap to match the origin coordinates in the Revit model, including the xy angle to True North. Then insert Origin to Internal Origin and it pops in perfect. You lose the coordinate system in Recap but it's just an intermediary anyway.