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Essentially what I am trying to do is:

  • Take an Observer point (using lat/lon)
  • Calculate the dates for the next equinox and solstice given a starting date
  • Find the Sunset Azimuth for each
  • Find the Sunrise Azimuth for each

*Please note, I am working in ArcGIS, so some of my values are pulling from an outside table

Here is kind of what I have:

sun = ephem.Sun()
final = ephem.Observer()
final.lon = row[1]
final.lat = row[2]
final.elevation = row[3]

equinoxDate = ephem.next_equinox('0001/01/01')
equinoxSetDate = final.next_setting(ephem.Sun(), start=equinoxDate, use_center=True)
final.date = equinoxSetDate
sun.compute(final)

print sun.az

I keep getting hung up on the "next_setting" part. I get NeverUpError... if I switch it to previous_setting, next_rising, previous_rising... it doesn't matter. I always get a NeverUpError or AlwaysUpError.

If someone can help me get it to find the Azimuth for an Equinox Sunset (on any date) then I can figure out the rest I am sure.

Let me know if something isn't clear.

THANKS!

Spatial Pariah
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  • So that we can try this code out on our own computers and have it run and give the same results that you get: could you share with us what the value of `row` is when you start this script? Generally, we have to be able to run your script ourselves to figure out its behavior. :) – Brandon Rhodes Apr 20 '13 at 01:29
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    I figured it out. I was getting errors because: final.lon, final.lat are treated as strings by pyephem. So I switched it by saying final.lon = str(row[1]) and went from there. Works great now! Brandon, you were on the right track with the values. :) – Spatial Pariah Apr 20 '13 at 01:41
  • If you could write up your findings as a quick answer and then mark it as the answer to this question, then this question will no longer show up as an “unanswered PyEphem question” in the browsers of those of us who watch for such things. Thanks! – Brandon Rhodes Apr 20 '13 at 16:10

1 Answers1

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I figured it out. I was getting errors because: final.lon, final.lat are treated as strings by pyephem. So I switched it by saying final.lon = str(row[1]) and went from there. Works great now! Brandon, you were on the right track with the values.

sun = ephem.Sun()
final = ephem.Observer()
final.lon = str(row[1])
final.lat = str(row[2])
final.elevation = row[3]

equinoxDate = ephem.next_equinox('0001/01/01')
equinoxSetDate = final.next_setting(ephem.Sun(), start=equinoxDate, use_center=True)
final.date = equinoxSetDate
sun.compute(final)

print sun.az
Spatial Pariah
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