Do you want to filter out obstructions from your survey? We’ve put together this document to help you pick the best filter for your dataset.
Propeller Smart Filtering is a classification tool that groups points within the constructed point cloud model into a specific class based on their characteristics. By bundling them, we can remove from the final elevation model.
Filtering out obstructions on site is an important aspect of monitoring assets and job progress. Whether it’s a shrub impeding a calculation of bare earth or a vehicle parked on a surface you want a gradient read on, filters help minimize such obstructions.
A point cloud is a set of points in a 3D system. Each point represents a location in space, and represents objects and terrain. When processing drone imagery, each pixel within the image has associated coordinates (X, Y, and Z). After your images are stitched together, these pixels are reconstructed into 3D point clouds of varying densities to replicate the area you just flew over.
Keeping that idea in mind, the three filter parameters are:
- Point Distance (m), which sets limitations on how far a point can be from the ground. The greater the distance, the more likely that the point belongs to a raised obstruction.
- Hold Size (m), which defines an area in which groups of points should be left untouched. This value can vary from a stockpile to a large building.
- Point Angle (deg), which defines a line between the ground and a raised feature. The greater the angle, the greater likelihood the point belongs to a vertical feature.
These work together. In order for a point to be classed as something other than “ground,” it has to meet all three criteria above.
How do you choose the filter best for your survey? You don’t have to. Simply identify the obstructions on site you’re most concerned about hampering your data, and we will choose a filter to remove them. The list below gives you an idea of what we can filter out of your 3D surveys.
When choosing a filter, keep in mind that bare earth can only be rendered where the camera can see. If the camera cannot see it, the filtering will cut away as much of the obstruction as possible, but may not provide a completely flat surface below.
- Equipment—Filters out cars, trucks, and heavy equipment. This is the best choice for measuring stockpiles.
- Vegetation—Takes out the plants. You’ll see bare earth underneath trees, shrubs, etc. The exception to this is when the vegetation is dense enough that the camera cannot see the ground.
- Structures—Flattens large objects with vertical faces. Stricter filter than Vehicles & Equipment.
- Everything—Filters out all raised features, including plants, equipment, and buildings. Should only be used on flat sites.