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Adding Survey Coordinates

The following article demonstrates working with artificial targets with known survey coordinates and adding them to a Vercator project.

It also contains definitions for the accuracy report.

Step-by-step guide

  1. Run all Vercator processing steps except the final scan transformation stage.
  2. Open the survey coordinates window from the Tools menu.
  3. Add the targets including their survey positions by pressing Add target and filling in the details as shown below.
    Alternatively import survey data from a csv file using the Import targets button.
    Vercator - Import Targets

    Survey Data CSV
    CSV file must be formatted with these fields only: point name, x, y, z
    Vercator - Imported Targets

  4. Identify the added targets in the scans by selecting the scan name from the list or from the 3D Target locations view.
  5. Right click to select the target position and select the correct target name from the list as shown below.Vercator - Target PositionVercator - Target Position 2

    Target Calculation Note
    With 1 target, only translations are calculated. With 2 targets, translations + rotation around z-axis are calculated. With 3+ targets translations + full 3-axis rotations can be calculated.

  6. To view the accuracy of the result press the Report button to open the statistical result as below, which can be saved where necessary. See next section of definitions for a deeper explanation of the terms used.
    Vercator - Target Report
  7. Press export transformation. This saves the survey transformation to the external_transformation.csv file in the project directory and is needed to run the final export stage successfully.
  8. Run the final Scan Transformations processing step, with “Apply Survey Transformation” option enabled as below. The scans output by this stage now have the survey transformation applied to them.
    Vercator - Survey Transformation

Definitions

All error values are given with scientific notation, for example 7.89123e-3 is the same as 0.00789123 (or 7.89 mm if the units are metres).

Survey Coordinate Location

An external coordinate that is manually entered and measured independently from LIDAR scans. For example coordinates measured using a total station.

Identified Target Location (Identified Coordinate)

An in-scan coordinate that corresponds to a survey coordinate, i.e. a location in a scan point cloud that has been marked as being the location of the survey coordinate.

This location is currently an actual measured point from the scan point cloud, and chosen as the point which is closest to the position chosen in the scan bubble view. That means that the accuracy will depend on the point density in the region where the target is identified.

Survey Transformation

Survey transformation is a transformation that when applied to all scans, optimises the alignment between all entered target survey coordinate locations and the corresponding identified target locations.

Target Mean Position

The mean position of each identified target location in all scans, for a given target.

This location is calculated after applying the survey transformation.

RMS survey-position error

Root-mean-squared error between a target’s survey coordinate and all the identified target locations in scans where the target has been identified.

RMS Position spread

RMS error between the mean identified location of a target and all the locations in each scan where the target is identified.

(This can be used as an error measure of local registration accuracy, provided it is possible to accurately identify the target in each scan)

Survey Position Error

A distance between a target’s survey coordinate location and identified location. This is calculated for each scan where a given target has been identified.

This distance is calculated after the survey transformation has been applied to the scan. A large error indicates a mismatch between the overall entered survey coordinates and identified coordinates.

Scan to Target Distance

The distance between the identified target location and the scanner location in a scan.