Georeferencing Your Scan

An overhead view of a point cloud with scan targets.

Georeferencing

When you capture a point cloud with PX-80, it does not contain any information about its geospatial position. The origin point (0,0) is automatically assigned to the point where you began your scan—it is not fixed to any surveyed, real-world position. That means if you want to fuse it with other project data sets (CAD design models, topography, etc), you will need to align your point cloud to the geospatial coordinates of your project first. 

This guide will walk you through a few methods for georeferencing your PX-80 point cloud. It includes step-by-step directions for using ground control points (GCPs), registering the point cloud to a previously georeferenced scan, and aligning manually using GNSS time stamps.

Notes: PX-80 does not include an interface to georeference data on the device itself, so all alignment will be performed using third-party desktop software. Since it is possible to do this using a variety of software solutions, this guide will include general steps only. If you need more in-depth information about how to perform each step, see the help documentation that accompanies your chosen application—we have included reference links at bottom of this article.

These methods are considered a static transformation. That means they rotate and translate the point cloud into the correct coordinate system—they do not change the shape, size, or scale or the point cloud.

A zoomed-in overhead view of a point cloud with scan targets circled in red.

Method 1: Align with survey control points

Ground control points (GCP) are large targets that you place throughout your site before you begin scanning. By surveying these targets using an independent method, such as a total station, you can determine their real-world coordinates, and then use these coordinates as a guide for georeferencing your PX-80 data. If you have ever used ground control points to align drone imagery, you will find the GCP process for PX-80 to be very similar. ( See this great overview of GCPs.)

  1. Place or identify a minimum of 4 ground control points across your project site.
    • Possible GCP types: 
      • Targets or checkerboard markers
      • Spray paint survey marks (less preferred)
      • Corners of building columns, foundation, or other fixed items on site
      • Automatic GNSS checkerboards, like Aeropoint
    • Tips for selecting GCPs:
      • Pick targets with high color contrast so they will be easy to see in the RGB point cloud.
      • Avoid using small objects like road nails, as these are hard to identify/locate
  2. Survey your GCPs. Determine their geospatial coordinates using one of the following methods:
    • Total station
    • GNSS system
  3. Scan your site with PX-80, being careful to capture all control points.
  4. Upload the coordinate information from your GCPs and georeference your point cloud.

    We recommend using Geo-Plus Vision Lidar. Here is a list of general directions for performing this task, followed by two in-depth videos produced by Geo-Plus.
    1. Open point cloud
    2. Import CSV file with coordinate information
    3. Click to associate each CSV coordinate with a selected target
      It is very important to pick up the exact center of the marker survey point. One should zoom in, take time, and then correctly pick the center point. Otherwise, there will be some minor displacements
    4. Click ‘Apply’ to transform the point cloud to the real-world coordinates

Method 1: Registration using a List (Video Walkthrough)
Method 2: Registration using a List (Video Walkthrough)

Note on software: If you already have the licenses, point cloud tools from FARO, Leica Geosystems, and Trimble will also work to add coordinates. Autodesk ReCap is not a viable option, because it requires you to view your PX-80 data in an imagery view, preventing you from using the point cloud view. 

A zoomed-in overhead view of a point cloud with single scan target circled in red.

Method 2: Register to building models or drawings

If you have models or drawings for your asset, and they are already placed within your project coordinate system, you can align the point cloud directly to these data sets using control points like building corners or foundations.

Some common CAD/BIM tools you could use include:

  • AutoCAD
  • Microstation
  • Civil 3D (Here’s a guide for importing point clouds into Civil 3D.)
  • Revit

Method 3: Register to a previously georeferenced point cloud

If you have previously captured and georeferenced a point cloud for your site using a UAV or terrestrial scanner, you can register your PX-80 data to that point cloud to georeference it. 

To do this, simply use the cloud-to-cloud registration function in your preferred point cloud software.

The result of a geolocation by cloud-to-cloud registration.

Method 4: Manually align to GNSS timestamps

If you have an independent GNSS device, you can use its data timestamping as a guide to georeference your data. 

  1. At the same time as you scan with PX-80, use the GNSS to log for the duration of each scan
  2. Generate a TXT file from your PX-80 with timestamps and relative coordinates from the 0,0 from the start of the scan. 
  3. Align the timestamp from the NMEA GNSS file with the timestamp of each PX-80 scan. (This is a manual process right now, we’re working on automating this alignment).

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