Subtract elevations from z-values

jeromecranston

Newbie here, is there a simple way to normalize a point cloud (convert z-values from height above sea level to height above ground) by subtracting z-values from an underlying Bare Earth GeoTIFF?

jeromecranston

That did the trick, Thank you :)

bmg_mike

You can do the following to subtract Z values from Lidar point Z values:

1) On Adjust Elevations tab of Options dialog for terrain (Bare Earth GeoTIFF), set scale factor to -1 to invert values

2) Select Lidar points to adjust with Digitizer Tool

3) Right-click and select the Analysis/Measurement -> Apply Elevations option

4) Choose to add the elevations from the terrain like below:

Thanks,

Mike

Global Mapper Guru

jeromecranston

Thank you for your suggestion, what that did though was turn the elevation values to negative (-510m instead of 510m).

bmg_mike

I just tried the workflow and it updated the Lidar elevations to be relative to the grid surface. The grid itself would show up negative, which is required to subtract by adding. If you change the scale on the grid back to +1 after applying to Lidar, then it will be back at the appropriate elevations.

When you applied the terrain to the selected Lidar, did you check the option to 'Add the New Elevation Value to the Existing Value'? If you just had the 'Replace It' option checked then you would have the negative values.

Thanks,

Mike

Global Mapper Guru