Creating Complex Boundary and Coverage Areas in Global Mapper
Creating boundary and coverage area polygons provides a way to clearly display the extent of the features in a layer using either a minimum bounding rectangle (MBR) or an irregular polygon that conforms to the geometric extent of the features in the layer. Using Global Mapper, this process is easy and is performed with only a few steps. Boundary areas can display the coverages of many different features such as town extents, real-estate zones, and much more. This blog demonstrates how to create a forest area boundary with a buffer by calculating a tree and building coverage area from extracted lidar points and finding the difference between the two layers.
We begin with unclassified lidar data and classify the building and tree points using Global Mapper’s Auto-Classification tools included in the Lidar Module. Next, we extract the building footprints and tree points using the Extract Vector Features tool. These steps create polygon and point features from the lidar point cloud that can be used to create the boundary polygons. Buildings and Trees after feature extraction
Right-clicking the created tree layer in the Control Center and navigating to Layer > BBOX/COVERAGES creates the coverage polygon, showing the tree points’ extent. This function determines the approximate outline of any raster or vector layers in Global Mapper. When creating polygonal coverage areas, the smoothing factor determines how tightly the coverage area matches the layer’s features; the rougher the area feature, the more imperfections show in the boundary, closely matching the actual coverage.
Tree area coverage with extracted buildings
Although there are trees in the urban areas, we want to show those regions that are heavily forested with no buildings. We can achieve this by creating another coverage area and performing a Difference operation using the building footprint feature as the area of interest. The two separate coverage areas overlap each other, one for the trees and one for the buildings.
Tree area coverage overlapping building area coverage with extracted buildings
By performing a Difference Spatial Operation with these two layers, a new layer consisting of zones from the first input layer that does not overlap features in the second input layer is created.
Difference performed between tree and building coverage areas with extracted buildings
Another process we can perform on the new converge area is the creation of a buffer area. The Create Buffer Around Selected Feature(s) tool creates an area around selected features based on a defined distance. For example, if we want to identify buildings within a certain distance of the forested area, we can add a buffer to all of the polygons in the forest coverage layer and run an advanced selection. First, we select the coverage polygon and click the Create Buffer Around Selected Feature(s) button. In the resulting Buffer Area Creation Setup dialog box, we input the required distance from the forest to create the buffer, which makes a bounding box around the forested areas.
50-foot buffer around the forested coverage area
To select any buildings within the buffer area, simply right-click the map with the buffer selected and navigate to Advanced Selection Options > Select All Area Features Enclosed within the Selected Area(s).
The selected buildings completely contained within the 50-foot forested buffer area
If you’d like to perform complex boundary queries yourself or learn more about Global Mapper and Lidar Module, download a 14-day free trial and request a demo today! For more information, contact us.