Global Mapper allows you to automate the process of locating features on
the ground by using Lidar data in 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 an entire point cloud
or a user defined subsection. This lidar feature extraction tool allows
the user to derive features such as building footprints, building roof
structure, power lines and other structures from classified Lidar ground
points.
Optional settings for extracting building roof and tree top polygons are
available in the Lidar Feature Extraction
Settings menu (below).
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 classification tool only on points selected
by the Digitizer.
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.
Extract 3D Building Footprints - Select
this for extracting building footprints and other, similar features from
classified ground points.
Create Separate 3D Areas for Different
Roof Pieces if Possible - Select this option to identify roof features,
this requires high resolution Lidar data and may not be possible with
all data sets.
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 Side Wall Area Extending to Ground
- Select this to create 'side walls', which extrude to ground from each
roof area edge.
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.
Extract Tree Points - Select this for extracting trees from
classified ground points. This option creates point features located at individual
tree tops.
Minimum Tree Height - The minimum height above ground for a tree.
Minimum Tree Spread -The minimum width (edge-to-edge) of a single tree.
Maximum Tree Spread - Specify the maximum tree (canopy width expected per tree) spread in meters.
Select Create Approximate Tree Coverage
Polygons to extract tree top polygons.
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 - Define shortest allowable powerline segment.