mentioned this earlier: when I do elevation calculations on lidar data - las input and gridded to a certain GMG I notice what I call: ghost precision. This is a precision (way) beyond the input precision.
In this case the LAS input is mm precision - as is standard in lidar input data, so 1.123 meters.
When doing calculations I frequently see numbers appearing far beyond the input precision. Including rounding to insignificant precision like 19.00000999 mm (see example)
Typical workflow allows LAS analysis GMG settings on the input to be set as meters of feet (I work in meters) to convert las data to GMG.
I typically use an average (binning) within a gridcell - so basically the average is the total elevation / divided by the number of points. The resulting number can never be more precise than the input precision:
1.123 meters + 1.122 meters = 1.1225 so should be 1.123m (and I will chose to use 1.12)
For further analysis and calculations (combine/compare, visualisation) I make sure to set the precision to cm (2 significant numbers). Still I notice that the RAW number displayed can have (not always, so: can have) a ghost precision, way beyond the cm level.
I don't know where the extra precision comes from. I guess from somewhere in the code.
Please note that more complex calculations might in theory lead to more figures behind the comma (like when doing a triangulation) but the result should never get beyond the input precision and should be rounded to the input precision. In an export the user should be able to round even further (p.e. to cm precision if wanted). You can do that to set the level in the export box.
I now manage the process because I am very careful in my procedure. I will remove the original LAS file and use the save GMG and load separately to avoid cross-over from the original files.
Please have a look at this!
Are there more users who noticed this behaviour?
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