[Liblas-devel] PROJ4 / Georeference info?

[Jason Woolard]

Thanks Howard. The problem is on my end. The strange thing is I can get 
this to work on a different computer. I remembered I was never able to 
get the win32 exe to properly install on my machine. No errors during 
the install it just doesn't import liblas. Martin R. gave me a DLL he 
made from a mingw compilation and I can get it to work by replacing 
liblas1.dll with his dll. Otherwise I get this:

 >>> from liblas import file

Traceback (most recent call last):
  File "<pyshell#16>", line 1, in <module>
    from liblas import file
  File "C:\pythonxy\python\Lib\site-packages\liblas\__init__.py", line 
1, in <module>
    from core import *
  File "C:\pythonxy\python\Lib\site-packages\liblas\core.py", line 112, 
in <module>
    las = ctypes.CDLL(lib_name)
  File "C:\pythonxy\python\lib\ctypes\__init__.py", line 348, in __init__
    self._handle = _dlopen(self._name, mode)
WindowsError: [Error 127] The specified procedure could not be found

Everything had been working fine until now. I know it's a problem with 
my pc because I have 1.0.0 successfully installed at home. I haven't 
seen anyone else report this since 1.0.0 was released. Have you seen 
this issue recently? The only difference I can think of is one machine 
is XP home and one is XP Professional but that really shouldn't matter.


Howard Butler wrote:
> This works almost exactly for me...
>
>> >>> from liblas import file
>> >>> input = file.File('TO_core_last_clip.las')
>> >>> h = input.header
>> >>> h.proj4
>> ''
>> >>> h.proj4 =  '+proj=utm +zone=17 +ellps=WGS84 +units=m'
>> >>> h.proj4
>> '+proj=utm +zone=17 +ellps=WGS84 +units=m'
>> >>> output = file.File('junk.las',mode='w', header = h)
>> >>> output.header.proj4
>> '+proj=utm +zone=17 +ellps=WGS84 +units=m'
>> >>> output.write(input.read(0))
>> >>> output.close()
>> >>> del output
>> >>> output = file.File('junk.las')
>> >>> 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 '
>> >>>
>>
>
> The only thing I'm doing different is making sure to manually delete 
> the reference to output when working in the interpreter to ensure that 
> the file is actually flushed and not using 'header' as the name for my 
> header that I'm writing to the file to ensure that I don't have a 
> namespace collision or something.
>
> Other than that, is it possible our versions are out of sync?
>
>
> On Oct 30, 2008, at 2:25 PM, Jason Woolard wrote:
>
>> 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 '
>>>>
>>>
>>>
>