[Liblas-devel] LASPoint::IsValid

[Volker Wichmann]

Hi Howard,

Howard Butler wrote:

>
> On Oct 2, 2009, at 2:42 AM, Volker Wichmann wrote:
>
>> Hi,
>>
>> as there's some discussion on "invalid points" on the list at  
>> moment, I like to ask a question about the IsValid check which I  
>> have for some weeks now.
>
>
> Is this using las2las?  You can use the --skip_invalid which despite  
> its terrible name, means "skip the invalid check" (I think :) )
>
no, I've stumbled over the problem using the isValid check in my own 
code ... while importing MLS data to our software, I realized that some 
points above the scanner were obmitted (e.g. bridges above the car on 
which the scanner was mounted had dropouts)

>>
>> IsValid checks (amongst others) the ScanAngleRank to be in the range  
>> -90° to 90°. Our problem is now, that we have LAS files from MLS  
>> (Mobile Laser Scanning) which have scan angle ranks ranging from  
>> -128 to 128. So the check fails with this data.
>>
>> Does anybody of you know if the ASPRS is discussing this issue for  
>> the next LAS specification and will relax this constraint (-90/90)?
>
>
> http://lidarnews.com/open-source-software-licensing contains a lot of  
> my thoughts on this subject, but I'll boil it down to this:  The  
> specification is just a suggestion until there is a reference  
> implementation.  libLAS isn't the reference implementation, and the  
> ASPRS committee doesn't seem so keen on proclaiming one, so each  
> vendor can pretty much do what they want and call it a "LAS" file 
> (and  they do, too.  Boy do they ever).
>
yeah, that's true - it seems the LAS format is getting THE format in 
which you need to distribute your data (i.e. all customers expect to get 
their data in LAS format) irrespective of what information is actually 
available or useful. It's a pity - and I would like to see the libLAS 
being the reference implementation. Thanks again for all your efforts to 
provide such a nice library!

> With regards to scan angle, the committee tried to outright through 
> it  out for the 1.3 release before being beat back by complaints.   
> Evidently it isn't that useful.

ok ... let's see what the future will bring

>
> As far as libLAS is concerned, I was willing to tilt at the windmill  
> of validation earlier, but without the committee's sanction, it's 
> just  libLAS' word against whomever wrote the file.  Being strict  
> contradicts libLAS' desire to be widely used in the industry,  
> especially if we can't read everyone's crappy LAS.  To that end, I've  
> taken on maintaining a sample library <http://liblas.org/samples>,  
> which contains just about every file that a user comes on the list  
> complaining that libLAS can't read ;)  My hope is the number of  
> permutations of bad files with asymptotically approach zero as time  
> goes by.  Of course, the committee makes geometrically more  
> possibilities with every ridiculous (thank goodness 1.3 got scaled  
> back from its original form) specification release :)

Extending liblas to read crappy LAS seems somehow ok to me (how should 
we handle these files otherwise?), but I think it is necessary to 
establish a standard for LAS that is capable to deal with all sorts of 
laserscanning data in a standarized way. I feel this is not possible 
with the suggestions made for 1.3. I will take a more detailed look at 
your thoughts on the format and will try to talk to some people who may 
influence some of the vendors - hope against hope ;-)

Thanks,
Volker

BTW: Thanks for the 1.2.1 maintenance release - this simplyfies a lot 
for us! ... and excuse my english, sometimes I'm unable to express my 
thoughts corretly :-)

>
> Howard