Reconstruct offers the ability to use GCPs to geo-locate point clouds. Additionally, Reconstruct allows geo-location information to be added to BIM through the alignment tool enabling a GCP-based alignment.
Set Up GCP Alignment
In order to perform an alignment task using GCPs, the user needs to have:
- The Longitude, Latitude, and Altitude (LLA) values of a minimum of 3 control points in BIM. These control points can be the corner of a column, the corner of a door opening, etc.. Or, they can be objects modeled specifically as control points (adding elements in BIM for the purpose of alignment).
- The construction site must contain physical GCPs (tags) with known LLA values. Those physical GCPs are required to be seen in the captured images, and the 3D reconstruction needs to be conducted using those GCPs.
GCP Alignment Workflow
In the Alignment Tool, create new control points and place their pins on the desired locations in BIM (the locations for which you have LLA coordinates offered by the site surveyor).
- For each of these control points, add the LLA values as follows.
- After adding a minimum of 3 control points along with their LLA coordinates, use the "Auto Place" buttons next to each control point to place their pin on the correct locations on the point cloud. Click the "Align" button to geo-locate BIM and align it with the point cloud.
Since Reconstruct aligns the point cloud to BIM (while maintaining a reference to the correct geo-location of both), any new BIM which is originally aligned to existing models on a third party software (such as Revit or Navisworks) will still be aligned to the point cloud.
In case the BIM was not aligned, check and update the BIM coordinate system in the Data Manager and choose between using the BIM's shared coordinates system or internal coordinates systems.
Creating a New Point Cloud
When creating a new point cloud for the same location of the point cloud that was previously built using GCPs, run the new reconstruction with alignment to that previous point cloud to achieve the same location accuracy. This guarantees (given enough similarity between the new and old images) that the new point cloud will also be aligned to BIM.
In other words, running the point cloud with GCPs only needs to happen once, and every other point cloud of the same location can be aligned to that reference point cloud.