TerraMatch User Guide

Introduction

TerraMatch is a sophisticated tool for improving the accuracy and quality of the raw laser point cloud. It compares laser data from overlapping flight or drive paths and calculates correction values for the misalignment angles as well as xyz location errors. The comparison and correction value calculation can be either based on surface matching or on different types of tie lines. Tie line matching comprises points or lines on horizontal, vertical or sloped surfaces that can be used for matching flight/drive paths to each other, but also known point or line locations that enable the adjustment of the laser point cloud to control measurements.

Especially in mobile ground-based laser scanning, the mismatch between overlapping drive paths usally changes over time during a surveying campaign, depending on the quality of the GPS signal on different locations. This requires a fluctuating correction solution which can be achieved with control measurements and TerraMatch tie lines.

TerraMatch is also used for misalignment angle calibration which should be checked and possibly improved at the beginning of data processing. For this purpose, data is collected on a specific calibration side which offers a point cloud dedicated for the calibration task to the software. If the system includes several laser scanners, the calibration involves scanner-to-scanner matching.

TerraMatch must be accompanied by TerraScan or TerraScan Lite.

General data requirements

The input data must meet some requirements to enable the algorithms to work properly:

•The data set must contain multiple strips which overlap each other. Alternatively, a single strip can be compared against a dense set of known points.

•The data set must contain some well-defined surfaces or other identifiable features for placing tie lines -- matching can not be performed if all the data are hits in forest canopy where no meaningful surfaces or features can be detected.

•Time-stamped trajectory information must be imported into TerraScan.

•For systematic shift corrections (positional or angular), a trajectory must not overlap itself. Any trajectories which make a 180 degree turn and return over itself, have to be split into separate parts using TerraScan.

•Laser points must be linked to trajectory positions so that TerraMatch can derive the laser scanner position and orientation for each laser point. This requires that laser points and trajectories use the same time stamp format.

The specific data requirements for different processing workflows are described in Methods of line adjustment.

TerraMatch UAV

TerraMatch UAV is a lighter version of TerraMatch. It is dedicated to users that process only point clouds collected by Unmanned Airborne Vehicles (UAVs, also called Drones). UAV systems produce relatively small point clouds from a low altitude. The system is more unstable in the air. Often, less capable/expensive hardware is used which leads to a higher inaccuracy level of the raw data. Therefore, the improvement of the data accuracy by eliminating boresight misalignment and positional inaccuracies caused by a bad trajectory solution plays an important role in the processing workflow. The UAV version of TerraMatch is well suited for processing point clouds up to a few million of points.

TerraMatch UAV does not have any project capabilites. Tools can be performed on points loaded in memory but not on project level.

TerraMatch UAV is available only in a bundle with other Terrasolid UAV software versions, such as TerraScan UAV, TerraPhoto UAV and/or TerraModeler UAV. TerraMatch UAV must be accompanied by either TerraScan UAV or TerraScan.

The Function matrix provides a complete overview of the tools in the different TerraMatch versions.