[Liblas-devel] PROJ4 / Georeference info?

[Jason Woolard]

hi again,

Your example still returns an empty string for me:

 >>> input = file.File('C:\\liblas_test\\debug.las')
 >>> header = input.header
 >>> header.proj4
''
 >>> header.proj4 = '+proj=utm +zone=17 +ellps=WGS84 +units=m'
 >>> header.proj4
'+proj=utm +zone=17 +ellps=WGS84 +units=m'
 >>> output = 
file.File('C:\\liblas_test\\junk_srs.las',mode='w',header=header)
 >>> output.header.proj4
'+proj=utm +zone=17 +ellps=WGS84 +units=m'
 >>> output.write(input.read(0))
 >>> output.close()
 >>> output = file.File('C:\\liblas_test\\junk_srs.las',mode='r')
 >>> output.header.proj4
''
 >>>

Am I maybe using Proj4 incorrectly? I'm just trying to add the 
Projection/geoference info into the header where it doesn't exist. Also, 
If I understood the posts from you and Mateusz it is necessary to write 
something (even a zero record) if you are making any changes to the 
input LAS file?

Thanks again,
Jason




Howard Butler wrote:
>
> On Oct 29, 2008, at 10:27 PM, Jason Woolard wrote:
>
>>
>> Thanks for the great work here. The library is working quite well. I 
>> have another quick question though. Sorry if I'm missing something 
>> obvious.
>>
>> I'm trying to add projection and georeference info to LAS header 
>> files that currently don't have any projection info. I was thinking 
>> something like this would work:
>>
>> >>> from liblas import file
>> >>> infile = liblas.file.File('C:\\liblas_test\\debug.las',mode='r')
>> >>> h = infile.header
>> >>> h.proj4 ='+proj=utm +zone=17 +ellps=WGS84 +units=m'
>> >>> h.proj4
>> '+proj=utm +zone=17 +ellps=WGS84 +units=m'
>> >>> outfile = 
>> liblas.file.File('C:\\liblas_test\\debug_junk.las',mode='w', header=h)
>> >>> outfile.header.proj4
>> '+proj=utm +zone=17 +ellps=WGS84 +units=m'
>> >>> outfile.close()
>> >>> outfile = 
>> liblas.file.File('C:\\liblas_test\\debug_junk.las',mode='r')
>> >>> outfile.header.proj4
>> ''
>> >>>
>
>
>
> You have to write a point to the file or it is not valid.  I guess we 
> should update the wiki to reflect this...  I also wonder if maybe we 
> should have the writer try to throw an exception when nPoints is 0...
>
>> >>> input = file.File('srs.las')
>> >>> header = input.header
>> >>> header.proj4
>> '+proj=utm +zone=17 +ellps=WGS84 +units=m '
>
>> >>> output = file.File('junk_srs.las',mode='w',header=header)
>> >>> output.header.proj4
>> '+proj=utm +zone=17 +ellps=WGS84 +units=m '
>> >>> output.write(input.read(0)) # read the first point and write it 
>> to the file
>> >>> output.close()
>> >>> output = file.File('junk_srs.las',mode='r')
>> >>> output.header.proj4
>> '+proj=tmerc +lat_0=0.000000000 +lon_0=-81.000000000 +k=0.999600 
>> +x_0=500000.000 +y_0=0.000 +ellps=WGS84 +units=m '
>>
>
>