Filling in Degrees in a Circle (Astronomy)

tom tom1189 at removethis.verizon.net
Sun Aug 24 01:45:27 CEST 2008


W. eWatson wrote:
> tom wrote:
>> W. eWatson wrote:
>>> The other night I surveyed a site for astronomical use by measuring 
>>> the altitude (0-90 degrees above the horizon) and az (azimuth, 0 
>>> degrees north clockwise around the site to 360 degrees, almost north 
>>> again) of obstacles, trees. My purpose was to feed this profile of 
>>> obstacles (trees) to an astronomy program that would then account for 
>>> not sighting objects below the trees.
>>>
>>> When I got around to entering them into the program by a file, I 
>>> found it required the alt at 360 azimuth points in order from 0 to 
>>> 360 (same as 0). Instead I have about 25 points, and expected the 
>>> program to be able to do simple linear interpolation between those.
>>>
>>> Is there some simple operational device in Python that would allow me 
>>> to create an array (vector) of 360 points from my data by 
>>> interpolating between azimuth points when necessary? All my data I 
>>> rounded to the nearest integer. Maybe there's an interpolation operator?
>>>
>>> As an example, supposed I had made 3 observations: (0,0) (180,45) and 
>>> (360,0). I would want some thing like (note the slope of the line 
>>> from 0 to 179 is 45/180 or 0.25):
>>> alt: 0, 0.25, 0.50, 0.75, ... 44.75, 45.0
>>> az : 0, 1,    2,    3,              180
>>>
>>> Of course, I don't need the az.
>>>
>>
>>
>> If I understand you right, I think using interpolation as provided by 
>> scipy would do what you need.
>>
>> Here's an example:
>>
>> from scipy.interpolate.interpolate import interp1d
>>
>> angles = [0, 22, 47.5, 180, 247.01, 360]
>> altitudes = [18, 18, 26, 3, 5, 18]
>>
>> desired_angles = range(0, 361)
>>
>> skyline = interp1d(angles, altitudes, kind="linear")
>> vals = skyline(desired_angles)
>>
>> # that is, vals will be the interpolated altitudes at each of the
>> # desired angles.
>>
>> if 1:  # plot this out with matplotlib
>>     import pylab as mx
>>     mx.figure()
>>     mx.plot(angles, altitudes, 'x')
>>     mx.plot(desired_angles, vals)
>>     mx.show()
> I decided this morning and roll up my sleeves and write the program. I 
> plan to take a deeper plunge in the next month than my so far erratic 
> look over the last 18 or more months  It's working.
> 
> The above looks like it's on the right track. Is scipy some collection 
> of astro programs? mx is a graphics character plot?
> 
> I just hauled it into IDLE and tried executing it.
>     from scipy.interpolate.interpolate import interp1d
> ImportError: No module named scipy.interpolate.interpolate
> 
> Apparently, something is missing.
> 
> I posted a recent msg a bit higher that will probably go unnoticed, so 
> I'll repeat most of it. How do I get my py code into some executable 
> form so that Win users who don't have python can execute it?
> 
> 

Both scipy and matplotlib are not part of the standard Python 
distribution so they would need to be installed separately.  Scipy is 
useful for scientific data analysis, and matplotlib is useful for making 
plots.

Since you want to wrap everything into a  Windows executable, it's 
probably easiest for you not to use scipy.  At the least, I suspect it 
would make your executable file much larger, but I've never made a 
Windows executable so I don't know the details.

As for making an executable, I'm not the one to ask, but googling leads 
to this:
http://effbot.org/pyfaq/how-can-i-create-a-stand-alone-binary-from-a-python-script.htm
which looks like a good place to start.

Tom




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