Ground Classification & Terrain Models
Strip the trees, cars and buildings out of a survey and keep the ground. Ground classification runs in SkyGIS Pro on a point cloud already in your project, using SMRF or cloth simulation filtering. You get a ground-only point cloud in the project, a terrain raster you can download and, if you ask for it, a raster showing how many points sit behind each cell.
- Methods
- SMRF, cloth simulation filter (CSF)
- Outputs
- Ground points, terrain raster, point-count raster
- Scope
- Whole cloud or inside a boundary
SMRF or cloth simulation filtering?
Both separate ground from everything else, but they get there differently. Run each inside a small boundary on a representative patch of the site and compare the ground points before you process the lot.
- Simple morphological filter
SMRF
Works from a grid of lowest points, removes features that stand above the ground at increasing window sizes, then compares each point with the resulting surface.
- CSF
Cloth simulation
Turns the cloud upside down and drapes a simulated cloth over it. The points the cloth settles on are classed as ground.
Settings, inputs and outputs
- Input
- A point cloud layer in the project
- Boundary
- Optional, to process only part of the cloud
- Algorithm
- SMRF or cloth simulation filtering, with adjustable parameters
- Advanced
- Preprocessing and return-selection controls for sources that need different treatment
- Terrain grid
- Raster resolution and aggregation method
- Ground points
- A ground-only point cloud layer in the project
- Terrain raster
- An elevation raster to download, plus a coloured terrain layer for the map
- Point-count raster
- Optional. The number of points behind each cell
- Related processing
- Pro can also thin point clouds and generate ortho and raster maps, for example to prepare lighter clouds and raster overlays for ArchiCAD and Revit.
Checking a ground classification before you use it
Compare the ground-only points with the full cloud in a few typical places: an open flat area, a steep bank, and somewhere under trees or beside a building. Flat, steep and obstructed ground behave differently, and a setting that works on one can fail on another.
The point-count raster is the quickest way to find thin data. Cells backed by only a handful of points deserve less trust than the colour ramp suggests, and it is better to know that before the terrain goes into a design or a volume.
Once you're happy with it, the ground-only layer is a cleaner starting point for elevation profiles and terrain comparisons than the raw cloud.
Questions
Why classify ground before measuring volumes or levels?
So trees, parked plant and buildings don't count as ground. Volumes and levels then describe the earthworks, not the machines or vegetation on them.
What do I get from ground classification?
A ground-only point cloud in the project and a terrain model you can download for use in other software.
Do I need desktop processing software?
No. It runs in SkyGIS Pro on a point cloud already in your project, on the whole cloud or inside a boundary you set.
Will ground classification recover ground hidden by vegetation?
No. It can only classify points that were captured. Where the scanner recorded no ground, there is nothing to classify.
See it on one of your own datasets
Pro is priced around your team and data volumes. The quickest way to judge it is a 30-minute walkthrough on a dataset you already have.