The Key to Model Key Point Identification in Global Mapper Pro

Model key points are used when subsequent analysis is required outside of a traditional geospatial application, such as CAD environments or gaming and simulation scenarios. Identifying model key points is an important process used to reduce the size of a data set, both in point count and file size, while retaining important structural qualities of the data. Global Mapper Pro v26® introduced a tool that enables users to locate these points within a point cloud with the Model Key Point Identification Tool.

See how the decimated point cloud (right) that only contains key points maintains more points where additional structural information is required.

What Are Key Points in a Point Cloud?

The typical purpose for identifying model key points is to reduce the size of a point cloud without sacrificing fidelity to any 3D objects within the point cloud. Model key points are the integral points within a cloud that must be retained during decimation in order to represent important structures and characteristics accurately. Essentially, model key points often represent the fewest points required to make an accurate TIN, a triangular surface, of the features.

If you look closely at the above point cloud you’ll see this car near the bottom left. Unlike the flat ground that surrounds it, the car is a relatively complex shape with three-dimensional changes between points. The surrounding ground is flat, and generally unchanging, making many of the ground points redundant and unnecessary. As such, during processing many ground points were excluded from the key points list. On the other side, we know that the points that make up this car couldn’t be removed without changing the shape of the car as represented in the point cloud.

Key Points vs Lidar Thin Tool

Global Mapper Pro users may be familiar with the Lidar Thin tool. While both tools thin the point cloud, the Model Key Points tool makes a more thorough investigation in determining which points are important. The Lidar Thin tool lessens the resolution of the point cloud to a specified resolution while maintaining as much data integrity as possible (3D Thin) or based on elevation parameters. Key Points works to decimate a point cloud to the least amount of points required to represent the features in the data.

How to Find Model Key Points in Global Mapper Pro

Finding Key Points is as easy as opening the Automatic Point Cloud Analysis Tools and clicking Apply Flags.

The tool works by creating a TIN from the points in the cloud, thinned based on the shared resolution parameter, as vertices. Next, TIN faces with similar angles are combined until the number of faces is a fraction of the initial count based on the Reduction Level parameter. The points at the vertices of the remaining faces are then applied as the Key-Point flag.

Be sure to check your resolution settings at the top of the Classification and Extraction Shared Settings dialog. This affects how the TIN that the key points are derived from is made.

• The Reduction Level is an estimate of how much of the point cloud is being reduced. The final result will vary (a little) depending on the structure of individual features in the point cloud. The final reduction might be higher in point clouds that have many 3D structures as more points need to be retained to maintain the integrity of the data.
• The Max Face Angle setting assesses the angle of faces in the TIN layer. If a face exceeds this setting it will be considered a different object. Larger values highlight steeper areas.

Compare the Max Face Angle setting at the default 45 vs 60. The larger value is more strict, only keeping points in steeper areas. 

Once Key points have been identified, use the Lidar Draw Mode dropdown to Color Lidar by Key Point in the original point cloud. The red points are recognized as key points based on the parameters in the tool settings.

Key points can be labeled as a Flag, or as a point classification, meeting the LAS 1.4 standards. These labels function similarly in Global Mapper, in that both can be used in filters for display or in other processing tools. Applying key points as a flag is the default functionality, but classification is also an option for those users who are using software that doesn’t have the ability to read flags.

GIS Resources

Interested in learning more about the new tools available in Global Mapper version 26.0? See these blogs:

• The Global Mapper Insight and Learning Engine™(beta) Leads Expansion of Analysis Tools in Global Mapper Pro v26.0
• Improved Ease-of-Use, Editing, and Data Support in Global Mapper v26.0

Test the Model Key Point Identification tool for yourself with a free 14-day trial license. If you have any questions, please contact us!