Global Mapper can automate the process of locating features on
the ground by using Lidar classified data with the automated feature extraction tools
available with the Lidar Module. The default parameter values can be changed
by the user for improved results.
The Extract Vector Features tool can be used on classified ground points, either on an entire point cloud or on a user-defined subsection. This lidar feature extraction tool lets the user derive features such as building footprints, building roof structures, power lines, and other structures from classified Lidar ground points.
This tool requires a Lidar Module license.
Select which features to extract, choosing from Buildings, Trees, Powerlines, or Poles.
Specify the appropriate settings under each extraction type using the guidelines below.
Press Ok to perform the extraction. See also 3D Point Symbols for options representing the extracted point features.
Select Point Cloud(s) to Extract Features From – If more than one Lidar data set is loaded into workspace, specific Lidar layers may be selected, or unselected, for automated feature extraction. Check the option to 'Only Extract From Lidar Points Selected in Digitizer Tool' to run the classification tool only on points selected by the Digitizer.
Only Extract from Lidar Points Selected in Digitizer Tool – Pre-select a subset of points, and then check this option to only process the selected points.
Resolution to Extract at – This may be set to Point Spacings or Meters. Smaller distances will result in higher accuracy, but will require higher resolution lidar data. Those working with low resolution data can use a higher value.
The average Point Spacings comes from the calculated point cloud statistics. For consistent and repeatable results when working with multiple lidar files, it is recommended to specify an exact resolution for the extraction in meters, rather than using the calculated Point Spacings.
The building extraction tool will create 3D building vectors or mesh features based on points in the Structure/Building Point group.
The default display of extracted 3D buildings is controlled by Area Feature Types: Building - Floor, Building - Ground, Building - Roof, and Building - Wall. These styles carry over to 3D model buildings as well.
Simplified Building Footprints - Select this option to extract only the building footprints and other similar features from the classified ground points.
Pin Footprints to Height - Use this option to set the elevation for all generated building footprints features to a single value.
Simplified Planes - Select this option to identify and create roof features for extracted buildings.
Simplified Side Walls - Select this to generate side wall features extracted buildings.
Sharpen edges and stitch planes by adding points at planar intersections - This option will generate point features along intersections between planes. The points will be placed between pairs of nearby points that are contained in different planes.
Buildings as Mesh - If selected, the building roof will each be turned into a single 3D mesh feature.
Color Vertices by Lidar Intensity - Use this option to color the mesh vertices by the lidar intensity value at that location.
Footprint Line Simplification Epsilon - Use this field to specify, in meters, the distance from one vertex to another for the vertex to be removed when simplifying the building footprint features. Larger values will further simplify the extracted building features.
Maximum Distance to Plane - Set the maximum distance in meters from an identified plane a point can be to still be considered part of the plane.
Minimum Number of Points in Plane - Use this field to set the minimum number of points needed in an area to identify a plane and create an extracted building feature.
Minimum Footprint Area - User this field to specify the minimum size of a building footprint in square meters. Generated footprints smaller than the entered value will be discarded.
Select Create Approximate Tree Coverage Polygons to extract tree top polygons.
Powerline Extraction Settings
Extract Powerline Features – Select this option to extract powerline features from loaded or selected lidar points.
Maximum Distance from Best Fit Line – Define the maximum allowable distance from the mathematical determined Best Fit Line of Classified Powerline points, in meters.
Maximum Angle Delta Allowed – Maximum angle between points to define a colinear powerline feature.
Minimum Powerline Length to Keep – Defines the shortest allowable powerline segment.
Pole Extraction Settings
Extract Pole Points –Select this option to extract poles from points classified as transmission tower
Minimum Pole Height – Specify the minimum height required to create an extracted pole from a cluster of pole points.
Minimum Pole Point Count – Specify the minimum count of points that must be contained in a cluster of points to create an extracted pole point.
Maximum Pole Spread – Specify the maximum width of a cluster of pole points to create a pole point.
Mark Top of Pole – Check this option to create a point at the top of the pole. When unchecked, the point will be created at the bottom of the pole.
Specify Bounds...– Manually specify
the bounds for extraction.
Filter Points... – Contains additional settings for filtering points for classification by elevation and color values, Source ID, and existing classification. The user may also exclude all points outside of a specified scan angle.
Restore Defaults – Restores the default settings for the Auto-Classify Ground Points tool.