example5.py

#!/usr/bin/env python

"""
A GPSTk example featuring some file input and processing to
create a plot with matplotlib.

Usage:

  python sem_plot.py

"""
import gpstk
from matplotlib.pyplot import figure, show


# Read in data, strict=True makes dataSets a list rather than a generator:
header, dataSets = gpstk.readSEM("data/sem_data.txt", strict=True)

# Write the data back to a different file (their contents should match):
gpstk.writeSEM("sem_data.txt.new", header, dataSets)

# Read the orbit out of the data:
orbit = dataSets[0].toAlmOrbit()  # alm orbit of first data point

austin = gpstk.Position(30, 97, 0, gpstk.Position.Geodetic)  # Austin, TX

starttime = gpstk.CommonTime()  # iterator time to start at
starttime.setTimeSystem(gpstk.TimeSystem("GPS"))
endtime = gpstk.CommonTime()  # end time, 1 day later (see below)
endtime.setTimeSystem(gpstk.TimeSystem("GPS"))
endtime.addDays(1)
# %% Step through a day, adding plot points:
d = []
el = []
for t in gpstk.times(starttime, endtime, seconds=1000):
    d.append(t.getDays())
    xvt = orbit.svXvt(t)
    location = gpstk.Position(xvt.x)
    el.append(austin.elevation(location))


# Make the plot
fig = figure()
ax = fig.gca()
ax.plot(el)
ax.set_xlabel("Time (days)")
ax.set_ylabel("Elevation (degrees)")
ax.set_title("Elevation of a GPS satellite throughout the day")
show()