How to correct Building Artifacts in the DSM and Orthomosaic with the rayCloud - PIX4Dmapper

This article explains how to use planar surfaces or create a planar surface on the ground to correct building artifacts in the DSM and Orthomosaic with the rayCloud.

Note:

The orthomosaic is generated based on the DSM that was created from the Densified Point Cloud. Thereby, errors and noise present in the Densified Point Cloud will be reflected in the orthomosaic. These distortions occur because Orthorectification is used instead of Photo Stitching, for more information: Photo stitching vs orthomosaic generation.

When computing the Densified Point Cloud, the altitude of the points will not be perfectly estimated. However, errors and noise can be minimized with datasets that have high overlap, good visual content of the images, GCPs, etc.

These errors and noise result in altitude differences for points that are supposed to be at the same altitude: for example points that belong to the same edge of a building. This altitude difference explains the distortions that appear near building edges in the orthomosaic.

Important: This method preserves the geometry but requires a certain amount of manual work depending on the number of objects to correct. Before proceeding with this method, it may help to read these tips to correct artifacts: How to correct Building Artifacts in the DSM and Orthomosaic.

Planar surfaces can be used to correct the point cloud in building areas:

1. Draw one or several New Surfaces on the roof using the rayCloud: How to draw a Surface in the rayCloud.
2. In the sidebar, under the section Selection, select the check box Use for DSM and Triangle Mesh to use the surface for the DSM generation: Menu View > rayCloud > Right sidebar > Objects - PIX4Dmapper.

3. Once the surfaces are created, process step 3. DSM, Orthomosaic and Index again. This will remove the noisy points from the roof and create a DSM and Orthomosaic without artifacts.

See Figure 1. below.

If there is still noise, the noise can be reduced even more by creating surfaces on the ground:

1. Draw one or several New Surfaces on the ground next to the building using the rayCloud: How to draw a Surface in the rayCloud.
2. In the sidebar, under the section Selection, select the check box Use for DSM and Triangle Mesh to use the surface for the DSM generation: Menu View > rayCloud > Right sidebar > Objects.
3. Once the surfaces have been created, process step 3. DSM, Orthomosaic and Index again. This will remove even more noisy points from the roof and create a DSM and Orthomosaic without artifacts.

See Figure 2. below.

Warning:

When reprocessing step 3. DSM, Orthomosaic and Index, the previous outputs will be overwritten. In order to keep the original outputs, move the outputs to another folder before processing.

When processing step 3. DSM, Orthomosaic and Index, the orthomosaic may present distortions on areas covered by points where the altitude has been modified when creating surfaces.

Figure 1.

PIX4Dmapper rayCloud before adding surfaces

PIX4Dmapper rayCloud after adding surfaces roof

rayCloud before Surface created

rayCloud after Surface created

PIX4Dmapper DSM after adding surfaces roof

DSM before Surface was created in the rayCloud.

DSM after Surface was created in the rayCloud.

PIX4Dmapper Mosaic before adding surfaces roof

PIX4Dmappes Mosaic after adding surfaces roof

Orthomosaic before Surface was created in the rayCloud.

Orthomosaic after Surface was created in the rayCloud.

Figure 2.

rayCloud before Surfaces was created

rayCloud after Surfaces was created

DSM before Surface was created in the rayCloud.

DSM after Surface was created in the rayCloud.

Orthomosaic before Surface was created in the rayCloud.

Orthomosaic after Surface was created in the rayCloud.