by Dennis Collin
A client recently asked me how to control where a laser scan survey was positioned within an existing Revit project. The project was complex and contain many elements and the default position where the cloud was referenced was extremely hard to determine. I was asked how we could control where the laser scan would be placed initially.
It helps to understand Revit’s 3 Origin marker points. I have written about Revit’s trio of origins here: Revits 3 origins
Fig 1. Enabling the display of Revit’s 3 origin markers.
In terms of visibility control the origins are set as subcategories under site category.
In a typical project the origins will be located at various positions. In terms of positioning the point cloud users usually only need to worry about the position of the Survey Point (shared coordinate origin) or the Project Base Point (user definable origin) The internal origin is Revit’s default 0,0 origin which is used as a global default. For the purposes of referencing laser scan data, we can ignore it.
If the Laser Scan has had its coordinates located correctly and is properly georeferenced, the Point cloud should be linked using the Shared Coordinates option. As shown in Fig 3.
Fig 2. Scan positioned using Shared Coordinates Setting
Cloud file will be positioned correctly from the Shared Coordinate System’s origin.
Fig 3. Linking a scan file to the survey point.
The Shared Coordinate Origin (usually represented by the Survey Point, triangular marker) and orientated correctly from the True North, once linked the scans orientation follows the True North aspect.
However, If the laser scan has not been located correctly, link the scan using the Origin to Internal Origin option. This option is a little deceptive as it connects to the Project Base Point and not the Internal Origin as stated/expected. To be honest, this is a better option as it provides control and some flexibility to the positioning of the survey scan.
Fig 3 Origin to Internal Origin, locates the scan on the Project Base Point! This is good news!
The scans orientation will follow the Project North aspect.
Fig 4. Linking a scan to the Project Base Point aligns the scan to project north.
Therefore, to locate the Point cloud in the correct place, move the Project Base Point to the required position using object snaps or coordinate entry and then link the Point Cloud using the Origin to ‘Internal Origin’ Option.
The third option I don’t use too often, is the centre-to-centre option which brings the centroid of the scanned points to the centre of the view.
Fig 5. Only link a scan centre to centre for diagnostic purposes!
The scans orientation will follow the Project North aspect.
Fig 6. Use Centre to Centre placement for diagnostic purposes?
This centre-to-centre option isn’t so helpful, so I would recommend the previous two options depending upon how the point cloud has been configured.
If the Autodesk Recap product is available, it is possible to set a coordinate of a particular point which will influence how the file is attached within Revit. If not, a suitable position can be derived from the model or site survey notes.
I have found in certain scenarios Revit’s origins don’t always display on screen. This is especially the case if 3rd party add-ins have been used to perform task on a project. To address this problem, create a view template from a new file and use transfer project standards into the working project.
Another useful tip is to create a selection set of the project base point. This means on busy projects awkward selections can be easily made rather than using conventional manual methods and risking inadvertently moving the wrong element!
Fig 7. Selection Sets are an especially useful Revit function!
It should be noted working with other formats such as NWD coordination models linking to the Internal Origin will do exactly that. Which is a pity because linking to the project base point would be far more useful. I am hoping such options will be included in a future version of Revit.
Working with Laser Scan data, Selection Sets, and the setting up of Revit Project Templates are just some of the topics that are covered on our follow-on or custom Revit training courses. For more information talk to one of the team by clicking here.
Príspevky (0 komentárov)