[Liblas-devel] ReadPointAt bug

[Mateusz Loskot]

Howard Butler wrote:
> 
> On Apr 22, 2008, at 9:30 AM, Mateusz Loskot wrote:
>> Mateusz Loskot wrote:
>>> Howard Butler wrote:
>>>> I'm not sure, and we would need a spec hound to verify, but I think 
>>>> that the file in question is not following the spec.  It *says* it 
>>>> is 1.0, but it has a 28 byte record length (this would imply a 1.1 
>>>> version file, right)?  So, who are we to believe?  The file version, 
>>>> like we were doing, or the record length, which in this case 
>>>> produces the correct results?
>>>>
>>>> Mateusz, do you have anything to add on this?
>>> There are two identifiers that control LAS file processing:
>>> 1. LAS File Version (1.0 or 1.1)
>>> 2. Point Format ID (0 or 1)
>>> So, following combinations are valid:
>>> - point record size is 20 bytes
>>> 1.0 & 0
>>> 1.1 & 0
>>> - point record size is 28 bytes
>>> 1.0 & 1
>>> 1.1 & 1
>>> The libLAS strongly depends on what's written to the header, so this 
>>> information must be as stated above, otherwise we are dealing with 
>>> invalid LAS file.
>>> If the information in header is correct, then we likely are having a 
>>> bug.
>>> Which one is true?
>>
>>
>> OK, we know, we have a bug. We've discussed it with Hobu and use of 
>> the m_recordLength value should fix the problem:
>>
>> [16:23]  <hobu> should we rework the code to explicitly pass the sizes 
>> around, or is caching the recordlength good enough?
>> [16:24]  <mloskot> I don't think we need to pass sizes
>> [16:24]  <mloskot> The m_recordLength is set correctly
>> [16:24]  <mloskot> according to the format ID
>> [16:24]  <mloskot> see LASHeader::GetDataRecordLength()
>> [16:25]  <hobu> ok
>> [16:25]  <mloskot> The m_recordLenght value is set when header is read
>> [16:25]  <mloskot> So, it is IMO fine to use this value for offset 
>> calculations
>>
>>
>> I'll take a closer look at it and run some tests.
> 
> 
> Ok, I have fixed this with http://liblas.org/changeset/572 and 
> http://liblas.org/ticket/34
> 
> I will make a new release later tonight.

Hobu,

Thanks for that fix!
I'm comleting C++ unit tests, hopefully they'll help.

Cheers
-- 
Mateusz Loskot
http://mateusz.loskot.net