Creating a Topographic Map from a Point Cloud

A quality point cloud is a fantastic starting point for a GIS workflow analyzing and modeling the topography of an area. The tools available in Global Mapper Pro allow users to process a raw point cloud to bring meaning to the lidar returns and create many derivative data layers. With all the capabilities of Global Mapper Pro available at your fingertips, a topographic map, or 3D dataset comprehensively modeling natural terrain and manmade structures, can be generated from a single input layer, a point cloud.

Classification

A point cloud describes the vegetation, natural features, and manmade objects in a study area. The first step in creating data from a raw point cloud is classification. This process groups the points into defined classes that bring additional meaning to the point cloud data. Once classified, classes of points in the point cloud can be focused on or removed from consideration in the subsequent processes. 

Global Mapper Pro’s Automatic Point Cloud Analysis tool provides built-in class models for some commonly identified point cloud classes: noise, ground, vegetation, buildings, poles, and powerlines. Not all of these classes can or need to be identified in every dataset. For datasets that do, the tool in Global Mapper allows multiple classification routines to be executed with a single click. 

Moving beyond the basic classes, the geometric segmentation and custom classification functionalities in Global Mapper Pro can be used to identify features in the point cloud and apply additional classifications. In this dataset, geometric segmentation has been used to identify paved surfaces based on curvature and intensity values. A custom class is then applied to the identified ground points representing paved surfaces. Cars and other smaller features on the ground surface are left unclassified, making it easy to filter out these points in Global Mapper Pro.

Extraction

The central feature in this area of interest is a shopping center. To better model the building features on this property, vector features can be created from the point cloud using another section of Global Mapper Pro’s Automatic Point Cloud Extraction tool, extraction. Relying on a classified point cloud, the extraction section of the automatic analysis tool creates vector features representing the objects in the point cloud data. Since the point cloud is a 3D dataset, the vector features extracted from it are also 3D.

The custom- classified parking lot area in this dataset can also be extracted using point selection and a digitizer area feature creation option. With many different selection modes, along with the power of the point cloud segmentation tool in Global Mapper Pro, a bounding area can be generated for almost any feature identified in a point cloud.

Terrain

Since ground has been classified in this dataset, a raster terrain model, also known as a digital elevation model or elevation grid, can be created from only the ground representing points. The Create Elevation Grid tool in Global Mapper Pro provides multiple methods for grid creation as well as an option to filter the points by classification or other characteristics. By filtering to only the ground points and using a binning grid method, a bare-earth terrain model can be created.

Contour Lines

To gain further insight into the shape of the terrain in this area of interest, Global Mapper can be used to generate 3D vector contour lines from the terrain model now present in the workspace. Contour lines provide another layer of topographic information to a viewer of a 2D map. Generated in Global Mapper at the user set interval with vector labeling and styling options, contour lines help to describe the terrain of the area. 

Image

Global Mapper’s Create Elevation Grid tool is a bit misnamed as it holds the capability to generate image layers from other attributes present in a point cloud. If present in a point cloud RGB color values, intensity, classification code, and other attributes can be used to create an image layer for the point cloud area. In this workflow, the source point cloud does not contain RGB color values, but since it has been classified, the point classification codes can be transformed into an image. This gives some additional context to the area.

Creating the Map

All the layers created from the single point cloud layer this workflow began with can be displayed together to create a topographic map. Styling the vector features and ordering the layers in the workspace allows the fine-tuning of the data display for map presentation. Moving to the Map Layout Editor, a tool for creating maps for export to image or print, additional map elements such as a legend, scale bar, and title can be added.

With all the power of Global Mapper Pro’s analysis and editing tools, many different types of data can be generated from a single point cloud to generate a topographic map. To try out this workflow and other Global Mapper Pro tools with your data, download a 14-day free trial today!