Shared co-ordinated from point cloud

[nathaniel.mcmahon]

Trying to get shared co-ordinates from a pointcloud.

I have a point cloud in Recap with every point in a coordinate system.

I'm going to reset the cloud co-ords in recap to a point who's co-ords I've jotted down. 

Import pointcloud into revit. Locate shared co-ords to known point and manually add update the co-ords to the known values. I'm guessing the rotation will not need to be changed as the rest point cloud points will retain their interrelation.

Thing is how do I find a point in the point cloud once in revit. It's not like I can make a note of one that I can later locate in revit.?

[barthbradley]

I'm not sure I understand. Is your Point Cloud in a Revit File which is Linked into another Revit Project via Shared Coordinates?  

[nathaniel.mcmahon]

nope it's a recap file linked into the model

[nathaniel.mcmahon]

Now obviously revit doesn't want to deal with thousands of geolocated points. So I'm stripping the cloud to a relative local co-ord system but fuffing around trying to relocate it on a shared co-ord system. It's a very simple operation, just now clear way of doing it in Revit to my knowledge.

[barthbradley]

I'm lost. Revit Shared Coordinates don't work with Points Clouds. 

Maybe this info will help you:

https://knowledge.autodesk.com/support/revit-products/troubleshooting/caas/sfdcarticles/sfdcarticles...

[nathaniel.mcmahon]

I'd like to use the geo located co-ordinates from a point cloud as the basis of a shared co-ordinate system. Is there any practical way of dong this as there doesn't seem to be. I'm having to strip away geo information from the point cloud for it to work within the accurate mathematical bounds of a revit model but is there any way of practically putting that geo information back in with shared coordinates.

Ideally tagging a point and jotting down it's xyz then locating that point in the revit model to the shared coord. But you can't simply tag and find a point, it's a practical problem really.  Is there some workaround? Point cloud software for example cloud compare will automatically upon importing a point cloud will locate the cloud in a shifted local co-ordinate system and then upon export will reshift back to the original. Much like revit's shared co-ordinates, but revit fails to offer this and doesn't take into account that a proper point cloud is geolocated. 

[SteveKStafford]

Was a surveyor involved with the point cloud process? If not then it probably isn't related to the site or local coordinate grid system for surveying. Either way...

What I've done in the past is link the primary point cloud file into a blank Revit project using Auto - Center to Center. Move it so it is close the project origin. Then link the remaining point cloud files using the other option Origin to Last Placed. This way they will all line up with each other based on the first.

Now this file can be linked into your building and use Acquire Coordinates. The file separation  from the building also creates an opportunity to manage the loading of point cloud files (if there are many) if you make it a worksharing file and assign each point cloud to its own workset. This way I was able to load clouds for each floor individually...as I worked my way up the building.

It is also helpful to trim any point data that lies beyond the actual scope of work. In my case one project picked up adjacent building, trees and cloud cover even. They did the scanning at night with windows open because it was so hot (summer in Texas). It was necessary to eliminate that noise first so the file's scope wasn't much too large.

[nathaniel.mcmahon]

Hi Steve,
Thanks for the reply.
First off I'll explain that the cloud is derived not from terrestrial
scanners but an rtk drone via Photogrammetry. So there's just one cloud
who's points are located within an Irish grid OS.
I'm not sure from your description how the point cloud coordinates inform
the shared coordinates. You can't import a cloud with global coordinates
without accuracy errors.

But it may be useful for me in aligning an .las point cloud to a text based
cloud edited into a DTM for the purposes of turning into a topo surface
that way the point cloud and topo surface would be perfectly aligned. But
wait I don't think I can turn a linked point cloud into a topo, topo can
only be created from a text file point cloud with no coordinate system. I
just don't think Revit can do much here. Perhaps I should be using civil
for the coordination efforts?

[SteveKStafford]

The approach I described is agnostic to the real world, just getting the Revit model to relate to the point cloud in a way that both can be used.

What is the overall expectation? Put another way, what software is being used and expected that it will all line up? The Geolocation of the project can be established in Revit via the Location settings. That depends on Lat/Long data. It can also be acquired from a civil file that uses Geolocation (Revit 2018-20).

If you can get the point cloud file aligned with a civil file and the local grid system then that DWG file can be used to Acquire Coordinates. That ought to permit linking the Point Cloud by Shared Coordinates.