Hello,
Thank you for your replies.
Unfortunately, the solution proposed by mvolz47 could not be applied for powerline processing with the use of lidar data or,generated from them, Digital Elevation Model.
The fact is that among 1st shots, you could find shots that hit not only powerlines, but also trees (high vegetation). It is not possibleto separate them from each other. For that reason, there is no need to exclude from analysis areas without high vegetation.
I attach you a file with my testing data (Digital Elevation Model).
I would be grateful for your advice concerning ArcGIS tool, which could help me to generate powerlines.
Best wishes,
Malgosia