About the Z Threshold

The Z threshold parameter represents the maximum orthogonal distance to the plane under consideration required for a point to be classified. If the plane is a good fit, based on the plane fit parameter, new points are added to the plane during the surface growing if the points are less than the Z threshold value. The threshold value depends on the accuracy of the input point cloud data. In addition, the object of interest under consideration and the quality of the point cloud data would affect the value to use for this parameter. For example when using the planar filter to classify buildings, certain roof types might require a higher value for this parameter such as roofs with Spanish tiles where there might be significant surface roughness on the roof. If there is poor alignment amongst various LIDAR tiles or flight lines a higher value might be required. Finally, the value used for this parameter would typically not be much larger and not greater than two times the value input for plane fit. The Z threshold value is linear and the default value for this parameter is appropriate for most cases.

Effects of Increasing or Decreasing the Z Threshold

• Decreasing Value: Decreasing the Z threshold value will result in fewer points being classified. Lower values will result in fewer classifications because the points under consideration are required to be a 'tighter' fit to the given plane resulting in fewer points being classified.
• Increasing Value: Increasing the Z threshold value will result in more points being classified. Higher values will result in more classifications is because the points under consideration are allowed a 'looser' fit to the given plane resulting in more points being classified.

How to Modify the Z Threshold

Z Threshold Box

1. On the Planar Point Filter property page, type a new Z Threshold value into the Z Threshold box.
2. Click the 'Apply' button to commit the changes.