Change Detection and filtering Elevation Differences

AxelG · November 12

Hello everyone,

I am currently working on a topographic change detection project. I am taking two lidar point clouds roughly one year apart and comparing their differences to detect changes in elevation. Here is my workflow:

1) Load in both point clouds

2) Fit the two point clouds together with the LiDAR fit point clouds tool. I do this because there is an option to set the threshold for the maximum z distance. I set it to 0.3 meters since I want to try and fit all points below 0.3m but preserve changes above this value. This reduces noise in the final product.

3) I create GMGs for the two resulting fitted point clouds

4) Create a GMG difference map between these two GMGs using the "Combine/Compare Terrain layers" tool. I used the subtraction (signed) operation to account for both positive and negative changes between the two GMGs.

5) The resulting GMG is a difference map shown below.

Issue: Although I fit the point clouds to a threshold of 0.3cm, I still get difference values between -0.30 and 0.30cm in the final change detection GMG. Is there a way I can filter all points in the final GMG that fall between -0.30 and 0.30cm? I want to remove these points in the GMG and only have difference values above 0.30cm and below -0.30cm.

I know I can change the display shader, but I'm hoping I am able to crop these values out or set them to null since I need to do further analysis on the GMG.