Based on the documentation and the implementation in the Lidar Viewer - Ground Removal tools, it is likely that the reference vector used by the “pcfitplane” function in this case is the Z-axis, i.e. the [0,0,1] vector, unless explicitly specified otherwise.
The “maxAngularDistance” parameter in the Lidar Viewer - Ground Removal tools may represent the maximum angle between the estimated plane and the Z-axis, beyond which points are considered as non-ground points. This is consistent with the behavior of the “pcfitplane” function where the “maxAngularDistance” parameter can be used to specify the maximum angle between the estimated plane normal and a reference vector.
If you want to ensure that the plane fitting is constrained in a specific direction, you could explicitly specify a reference vector using the “referenceVector” parameter in “pcfitplane”. However, if you leave it unspecified, it will likely use the Z-axis as the default reference vector.
Note that if the ground surface is not flat, using a single reference vector may not be sufficient and may result in incorrect plane fitting. In this case, you may need to use more advanced algorithms or techniques, such as RANSAC, iterative fitting, or ground segmentation methods to accurately estimate the ground surface.
