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.
Max Co-Planar Angle Difference – Use this field to set the maximum co-planar angle difference in degrees for use for extracting separate roof pieces. For lower resolution data, use a higher value and for higher resolution data, use a lower value.
Max Distance From Adjacent Plane – Use this field to set the maximum distance in meters from adjacent planes to use for extracting roof piece features. For lower resolution data, use a higher value and for higher resolution data, use a lower value.
Create Building as 3D Model (Mesh) – If selected, the building roof and (if selected) side walls will each be turned into a single 3D mesh.
ADVANCED: Simplify Multiplier for Smoothing Buildings – Select this option to simplify the building outlines. The specified value is a multiplier of the bin spacing for the feature extraction operation. For example, if the extraction is set at 1 point spacing and a simplification of 2 is used, the simplification factor is then 2 point spacings.
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.