Hard to believe, but we’re already fifteen weeks into the new year. In that time span, Terrasolid has released thirteen updates for TerraScan, plus several for the other modules, each adding improvements, bug fixes and several new features to the products. One new feature that helps improve existing workflows and streamlines the extraction of information and analysis using LIDAR data is a Write Group Info menu command (TerraScan -> Group -> Write group info) for writing a list of groups, such as those which represent trees.
Group or object-based classification was something added to TerraScan in late 2016 to improve on efficiency for above ground classification. This proved to also enable better automated or semi-automated analysis using LIDAR data. The ability to Inspect Groups provided the user a means to improve upon the accuracy of the results for reporting, but the reporting piece was limited and users asked for more attributes depending on what objects the group represented and an easier way to report the information.
The new Write Group Info tool helps fix this problem by making use of a new User group formats setting (TerraScan -> Settings -> File Formats -> User Group Formats) for writing a list of each group and its attributes. Two are configured by default, “Tree– highest point” and “Tree — trunk”, to provide an example of how they can be used, and the attributes that can be determined from the groups.
Figure 1 : Example User Group Format For Tree Groups Derived Using The Highest Point Method
Some attributes are readily derived at run time from the points belonging to each group or the geometry of the group itself, such as average easting, average northing, point count, or ground Z. An elevation at ground attribute is computed at write time using a TIN generated from the specified ground class. On the other hand, some attributes, such as biggest distance, smallest distance, or trunk diameter, require additional information be derived and available before writing the group info. I detailed the distance attribute back in October 2020 showing how it could be used for height from ground, or fall in/grow in values for objects. Trunk diameter at breast height is probably the most requested parameter and now it too can be derived from LIDAR data using TerraScan.
Trunk diameter at breast height
To write out the trunk diameter at breast height, one must first have a tree classification that was derived from groups assigned using the trunk method. Hence, would only be applicable for those datasets where the data density and/or look angle, such as mobile, provides for sufficient visualization of the tree trunks. Then, run the new Measure Trunk Diameters tool (Trees -> Measure Trunk Diameters) to generate circles on a CAD layer representing the diameters at breast height. Edit as necessary or desired. Then, provide the trunk diameter layer when writing group info using the “Tree — trunk” format.
Figure 2 : Circle Elements Produced By Measure Trunk Diameters Terrasolid
Figure 3:Measured Trunk Diameters at breast height
The new Write Group Info and Measure Trunk Diameters tools improve and streamline existing workflows for leveraging LIDAR data to improve the analysis of project areas. Coupled with UAS based LIDAR that can increase the frequency of monitoring small sites at high resolution, or the newer high end traditional aerial systems with increased point density and better scanner arrangement to achieve more vertical structure resolution, these new tools make use of the above ground point information and shows the potential of LIDAR data beyond simply a digital elevation model. We offer training in all Terrasolid workflows for users in North America. Contact us if you’d be interested in learning more about this or other workflows.