I'm creating an app to predict satellites visible passes. In the app, I use 'if' statement to decide whether or not a satellite would be visible.
like follows;
if satellite.neverup is False and satellite.circumpolar is False:
observer.next_pass(satellite)
This computation works fine for most of LEO satellites.
However, I found some curious results. The next_pass function used before satellite.compute(observer) and after return different values.
Following code reproduce the result.
import ephem
line_0 = '0 SL-3 R/B'
line_1 = '1 12904U 81103B 14252.72400340 .00001812 00000-0 13444-3 0 5754'
line_2 = '2 12904 081.1813 349.2718 0030677 147.5032 212.8569 15.02708918340741'
target = ephem.readtle(line_0,line_1,line_2)
site = ephem.Observer()
site.lon = '151:43:00'
site.lat = '-27:26:00'
site.elevation = 400
site.name = 'test facility'
site.horizon = '40:00:00'
site.date = '2014/9/20 00:29:10'
print ephem.__version__
print site.next_pass(target)
target.compute(site)
print [target.neverup,target.circumpolar]
print site.next_pass(target)
Results are follows;
3.7.5.3
(2014/9/20 01:55:43, 303:49:09.6, 2014/9/20 00:25:02, 30:44:01.7, 2014/9/20 00:30:10, 164:08:09.1)
[False, False]
(None, None, None, None, None, None)
How can I avoid this result changing? Where am I wrong?
Thank you in advance.
After playing around for a while, and using other TLE's, a thought I have is that neverup is not properly accounting for your horizon. Perhaps it is using 00:00:00 to define the boolean; if you change the horizon to 30:00:00 the output becomes:
3.7.5.3
(2014/9/20 01:55:43, 303:49:09.6, 2014/9/20 00:25:02, 30:44:01.7, 2014/9/20 00:30:10,164:08:09.1)
[False, False]
(2014/9/20 12:06:25, 191:15:15.1, 2014/9/20 12:08:23, 82:43:37.8, 2014/9/20 12:10:20, 1:10:09.6)
For further debugging, we can print the altitude of the satellite at the next pass shown here. i.e.
info = site.next_pass(target)
site.date = info[0]
target.compute(site)
print target.alt
this gives:
31:07:31.3
Now if we change the altitude to something like 34:00:00, we get your list of None's back.
My guess is that neverup is not taking your defined horizon into account, but next_pass is.