Filling in Degrees in a Circle (Astronomy)

[W. eWatson]

Maric Michaud wrote:
> Le Saturday 23 August 2008 01:12:48 W. eWatson, vous avez écrit :
>> 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.
> 
> Not sure I got it, but is that fulfill your specs ?
> 
>>>> [20]: def interpolate(a, b) :
>     slope = float(b[1] - a[1]) / (b[0] - a[0])
>     return [ slope * float(i) for i in xrange(b[0]-a[0] + 1) ]
>    ....:
> 
>>>> [23]: interpolate((0, 0), (180, 45))
> ...[23]:
> [0.0,
>  0.25,
>  0.5,
>  0.75,
> ....
>  44.5,
>  44.75,
>  45.0]
> 
>>>> [29]: interpolate((80, 20), (180, 45))
> [0.0,
>  0.25,
>  0.5,
>  0.75,
>  1.0,
>  1.25,
> ...
>  24.5,
>  24.75,
>  25.0]
> 
> 
> 
Yes, the interpolation part looks right, but the tricky part is to be able 
to go through the list and find where one needs to generate all the missing 
az angles. A chunk of my data is in a post above yours. Here's a more 
revealing set of data where four data points are known:

az el
0 10
4 14 (slope is 1)
12 30 (slope is 2)
15 15 (slope is -5)


16 points need to be generated, 0 to 15, representing 15 degrees around the 
circle.
So, I'm doing this in my head, one would get
0 10 (slope is 1)
1 11
2 12
3 13
4 14
5 16 (slope is 2)
6 18
7 18
...
12 30
13 25
14 20
15 15

I use Python occasionally, and starting up requires some effort, but I've 
finally decided to take a go at this.

I'm working on this now, but my knowledge of python needs refreshing. Right 
now I have a file of all the az,el data I've collected, and I'd like to open 
it with Python for XP. However, Python doesn't like this:

junkfile = open('c:\tmp\junkpythonfile','w')

I get
     junkfile = open('c:\tmp\junkpythonfile','w')
IOError: [Errno 2] No such file or directory: 'c:\tmp\\junkpythonfile'

This problematic segment is just a hack of a similar statement which has the 
same problem and a much longer path. I suspect the problem is with the back 
slash.

-- 
            Wayne Watson (Watson Adventures, Prop., Nevada City, CA)

              (121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
               Obz Site:  39° 15' 7" N, 121° 2' 32" W, 2700 feet

                     Web Page: <www.speckledwithstars.net/>