Measuring Precise Distances in Point Clouds

The video below shows the steps to use to compute precise distances between faces of structures in point cloud data. The request here was to provide a way to take point cloud data and be able to provide an accurate measurement for the separation between a concrete face of the building and the front face of pearlings (Steel columns) that are attached to the front face of the concrete onto which some architectural “cheese grater” detail is added to the face of the building. The measurements will provide detail for the steel erector to determine the shimming required at each location where the steel pearlings and building can be seen in the same locations. The building is not a perfect face nor is it perfectly plumb or perfectly straight so of course each point determination is unique.

The pearlings are visible only in certain areas, as is the concrete because the cheese grater facade is already in place.

Station View of the project

The process that we recommend here is as follows

  • Find the elevation of the horizontal plane that cuts through the visible concrete wall where you can also see the pearlings - in this case the planes were separated by 6.5’
  • Use the Plane Manager command to create cutting planes at each of the horizontal plane elevations
  • Use the cutting plane view using the cutting planes that you defined, one at a time to slice the building point cloud regions that you have available - note that it is beneficial to create point cloud regions for the data that you are trying to analyze rather than trying to use the whole point cloud in each analysis - you will find that the calculation time for e.g. the best fit lines below and the selection of the point cloud data will be much faster as a result.
  • Once the building point cloud has been sliced - you can select the thickness of the cutting plane to show some data above and below the plane to give you enough point cloud data to determine the location of the front face of the pearling and the front face of the concrete. Note that it is helpful at this point if you have managed to separate the Concrete Face Detail from the Pearling Detail as Point Cloud Regions.
  • Now you can select the point data that represent the front face of the pearling and use the Best Fit Line command from the CAD menu to find the face line of the Pearling as a 3D line. Repeat the process to find the front face of the concrete wall. DO this over a small area around the Pearling of interest and the concrete wall that goes with it.
  • You now have 2 lines for the pearling and wall. You can draw a 2 point line between the center of the face of pearling line and perpendicular to the face of concrete line. This line will be a 3D line so will have a Slope Length and a Horizontal length. The Horizontal length is the separation between the face of the pearling and the face of the concrete.
  • If you need precise point locations for these points you can use the Point Creator Command to create 3D points at the ends of these lines. If you want the lines to be horizontal, you can review the Min Max Elevation of the lines and use the Change Elevation or Adjust Linestring Elevation Command to set the elevation to a single value - that way they now only have a Horizontal length. If you set the elevation to be the same as the datum plane that is going to give you the best results.

If you then want to compare these to a “design” location for where the face of the building was meant to be (in a perfect world where the building was built to an accuracy of 0.01 to the Design), then if you build a 3D polygon representing that face you can compare the Concrete Points and or the Pearling Points to that polygon using the Face Analyzer or the Perpendicular Distance to Surface commands to determine those values also as needed.

The video shows the process used.