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/>
--
http://mail.python.org/mailman/listinfo/python-list
