Deduce using time
Deduce using time command assigns line numbers to laser points based on time stamps and imported trajectory information. The process looks at the time stamp of each laser point, finds a trajectory which covers that time and assigns that trajectory number to the laser point.
The command is the easiest way to make sure that the line numbers of laser points match the trajectory numbering.
The process of deducing line numbers works only correct if the time stamps of laser points and trajectories are unique. This may cause a problem, for example, if time stamps are stored in GPS second-of-week format and if you have loaded multiple flight sessions from the same week day but different weeks. If both, laser points and trajectories store time stamps in GPS standard time format, the time information is unique and there are no roll-over problems between different weeks.
Matching time stamps of laser data and trajectories are required for a number of processing steps, especially in TerraMatch but also in TerraScan.
To deduce line numbers from trajectories:
1. Load trajectories into TerraScan.
2. Select Deduce using time command from the Line pulldown menu.
This assigns the trajectory numbers as line number attributes to laser points. An information dialog shows the number of points that were effected by the process.