Creating 3D Buildings from Lidar Data in Global Mapper
Creating and displaying buildings as multifaceted three-dimensional (3D) features is a realistic way to represent an urban landscape. With Global Mapper and the accompanying Lidar Module, it is easy to extract 3D buildings in vector format from lidar and other point cloud datasets. In this blog, we discuss two feature extraction methods for generating 3D building models. The Extract Vector Features tool analyzes the geometric characteristics of points classified as buildings and automatically creates the corresponding structural planes, while the Custom Feature Extraction tool utilizes the Path Profile window to display a series of cross-sectional views of the point cloud for accurately creating one building at a time.
To extract vector features, it is necessary to first identify and classify points that represent buildings, which can be done using the Lidar Module’s Auto-Classify Non-Ground Lidar Points tool. Subsequently, the Extract Vector Features tool is used to extract the footprints, roof structures, and walls of each building.
3D Viewer displaying the extracted building features
Under Building Extraction Settings in the Lidar Feature Extraction Settings dialog box, the Extract Buildings option creates 3D building vectors derived from points classified as buildings, according to ASPRS lidar classification specifications. Extracted buildings can be generated as footprints or as 3D objects containing area features for the roof planes and sidewalls. They can also be generated as 3D models photo-textured with real-world colors if RGB values are included in the attributes of the point cloud.
In the example above, the options selected include: Building Footprints which creates polygons coinciding with the extent of the classified points; Regularize to smooth the building footprints with parallel walls and 90-degree angles; Roof Planes that identifies and creates elevated roof features for extracted buildings; and Side Walls which generates vertical polygons coinciding with the building walls. Also enabled is the Sharpen Edges and Stitch Planes by Adding Points at Planar Intersections that creates point features along intersections between planes and smoothly stitches together pitched roofs.
Lidar Feature Extraction Settings dialog box to extract the buildings
After extraction, the newly created vector features are rendered in the 2D map as polygons. In the 3D Viewer, the walls and roof planes are displayed as 3D objects. The buildings are comprised of vector area features that can be moved and reshaped, can have attributes added, and can be symbolized with various area fill and border options. The building layer can be exported to various supported vector formats, including shapefile, dxf, geojson, geopackage, and many other options.
For more precise building features, an alternative, hands-on method for creating 3D buildings is described below.
The Custom Feature Extraction procedure involves the use of Global Mapper’s Path Profile tool, which is more typically used to render a cross-sectional view of raster terrain data. When used with a point cloud, the path along which the profile is created is effectively buffered, so a user-defined swath of points is displayed. In order to use the Custom Feature Extraction tool, a series of equally spaced profiles perpendicular to the defined path is created, and within each of these views, the position of each vertex in the extracted feature is determined.
Extracted building with a pitched roof in the 3D Viewer
To extract 3D buildings with this tool, we first change the Path Profile Settings and enable Display Series of Profiles Perpendicular to Path, so that cross profiles are generated across rather than along the path. A Perpendicular Path Length larger than the building’s width is set with a distance that is sufficient to display the entire roof in the profile. The Perpendicular Sampling setting is used to establish the distance interval between each sequential profile view. This distance ultimately determines the spacing between consecutive vertices in the extracted feature, so a smaller value will allow more precision in the structure of the building. The Display Lidar Points Along and Near the Path is also enabled under the Lidar Display Options (Requires Lidar Module) to allow the display of lidar points within the Path Profile view.
Path Profile Settings dialog box to set up for tool to display perpendicular profiles
To create the first profile view, we draw a path as close as possible to the building’s centerline. Ordinarily, this path would define the linear array of points that would be displayed in the profile window, but because we had selected the option to create perpendicular profiles, this initial line is simply used as the basis for each sequential view. After completing the line, the first swath of points is displayed in the Path Profile window.
Path Profile tool going through the center of the building where roof angles
In the Path Profile/Line of Sight display, the pitched roof of the building is clearly visible and the Move Next Perpendicular Profile can be used to display each of the profile views in order.
To initiate the 3D feature extraction process, the Extract Lines/Areas from Perpendicular Profiles button is selected, and vertices are created to represent the linear roof features. In this example, we generate one vertex at the bottom edge and one at the apex of the roof for both the left and right sides to create the two roof pane structures. By navigating through each of the sequential profile views, the precise position of each vertex is fine-tuned.
Pitch of roof displayed in the line of sight with the linear features created for the roof panes
After all of the vertices have been placed, a vector feature representing each roof plane can be generated. Before finalizing this extraction process, the polygons are limited to the roof’s extent by defining the start and stop of the perpendicular features through the Perpendicular Profile Options.
Modify Feature Info dialog box for feature creation of the roof
This workflow creates two polygons for each side of the roof and building, shown in the 2D map view. With the 3D Viewer opened, the structure is displayed as two abutting three-dimensional models.
If you’d like to create your own 3D building models from lidar data 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.