Prescribed scale values for LASvalidate
Howard Butler
I have been using the fabulously useful lasvalidate tool to comb through holdings of LAS files looking for issues. On bone I have to pick with the utility is its prescription of scale values to be a factor of 0.1 or a factor of 0.25 [1]. Was there a rationale for this? I know at one time there might have been a a little bit of language attempting to prescribe scale factors of 0.1, but neither of these scale factors work for all situations.
tl;dr. Why does lasvalidate prescribe scale factors be divisible by 0.1 or 0.25?
Howard
[1] https://github.com/LASvalidator/lasvalidate/blob/master/src/lascheck.cpp#L602
Martin Isenburg
Hello Howard,
This inquiry should probably concern the custodians of the LAS and LAZ formats so i added "The LAS room" in my reply.
You are part of the LAS Working Group (LWG) of the ASPRS and so I would assume you were part of those folks in charge of deciding on a set of reasonable validation criteria when the LAS Validation Suite (LVS) was originally discussed. I had been excused from the LWG discussions at the time as I was planning to bid on the tender. At first i was told that my bid had won but then it was cancelled half way through the contract signing a few weeks before the ASPRS president resigned, which, however, was really just a total coincidence ... (-;
That initial LVS specification tender document i received to write a bid for was quite detailed and explicitely asked for scale factors to be powers of 10. I assume this is what the 12 (or so) members of the LWG decided on. This made a lot of sense to me as this assures we have easy to describe resolutions (e.g. cm, mm, dm, tenth of a mm, ...) and discourage "resolution fluff". But since RIEGL uses quarters of a mm for some of their outputs i added anything ending in ....025 as an allowable unit as well. I am totally open to add other meaningful units as well such an anything ending in 05 or 175 but i would like to continue to fail 0.000067436863257 and similar scale factors as these suggest that the author created output that deletes all meaningful information about the resolution (like cloud compare does it right now) ...
Come to think of it ... I think we need a similar check for the offsets. They ought to be a even multiple of the scaling factors and not introduce "translation fluff" ...
Cheers,
Martin @rapidlasso
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