[Liblas-devel] GPS time and intensity?

[Howard Butler]

On Oct 12, 2008, at 6:08 AM, Mateusz Łoskot wrote:

> Jason Woolard pisze:
>> Two more quick questions. I can't seem to pull the intensity from a  
>> LAS file. The documentation shows intensity in the LASPoint class.  
>> Has that been implemented? I'm getting a Traceback error in Python  
>> 2.5 with intensity while x,y,z return_number and classification are  
>> all coming across fine.
>
> Jason,
>
> I'm not an expert of the bindings for Python but as I see, intensity  
> getter/setter is missing:
>
> http://liblas.org/browser/trunk/python/liblas/point.py
>
> Let's wait for Howard to confirm.
>

D'oh.  Of course we would find this the day of the release :)

Add the following to point.py:

     def get_intensity(self):
         return core.las.LASPoint_GetIntensity(self.handle)
     def set_intensity(self, value):
         core.las.LASPoint_SetIntensity(self.handle, value)
     intensity = property(get_intensity, set_intensity)


>> Also, the GPS time seems to be rounding to the nearest second . My  
>> input file has data to 3 decimal places. Is there any way to carry  
>> that precision over?
>
> Aren't LiDAR observations (pulses) measured in seconds with  
> fractions ignored?

I don't know the answer to this but the 1.0 and 1.1 specs say:

"The GPS time is the double floating point time tag value at which the  
point was acquired."

The spec isn't very clear on this, and while it is true that the  
<time.h> C functions don't deal with fractional seconds, it may be  
that vendors are using them.  Maybe we should ask on the USGS board  
about this question and see what people say.