Plotting Spacecraft in Earth Orbit (earthplot)

A plot of a spacecraft in orbit can be made by using the EarthPlot plotting class. This plot class takes advantage of the Cartopy API. To initialize the class, we can do the following:

>>> import matplotlib.pyplot as plt
>>> from gdt.core.plot.earthplot import EarthPlot
>>> earthplot = EarthPlot(interactive=True)
>>> plt.show()

This creates a plot of the Earth in a cylindrical projection. You can also easily create an image of a section of the Earth by defining lat_range and lon_range:

>>> earthplot = EarthPlot(lat_range=(-70.0, 70.0), lon_range=(0.0, 60.0), interactive=True)

We can also add a polygon representing a defined region for the South Atlantic Anomaly (SAA). This example uses the SAA region defined for Fermi GBM (see the Geomagnetic Module for more info about defining the SAA).

>>> from gdt.missions.fermi.gbm.saa import GbmSaa
>>> earthplot = EarthPlot(lat_range=[-30.0, 30.0], saa=GbmSaa(), interactive=True)

The SAA plot polygon object can be accessed:

>>> earthplot.saa
<SAA: color='darkred';
      alpha=0.4;
      linestyle='solid';
      linewidth=1.0>

And its properties can be modified:

>>> earthplot.saa.color = 'purple'
>>> earthplot.saa.fill = False
>>> earthplot.saa.linestyle = '--'
>>> earthplot.saa.linewidth = 2
>>> earthplot.saa.hatch = 'x'

Now, we want to show the orbit of our spacecraft and perhaps even plot the position of the spacecraft at a particular time. For this example, we will read from a Fermi GBM Position History file and use the SpacecraftFrame object (see Spacecraft Attitude, Position, and Coordinates for details about using the SpacecraftFrame class). This file contains the position history of Fermi for an entire day. We will select a time range over which to display the orbit.

>>> from gdt.core import data_path
>>> from gdt.missions.fermi.gbm.poshist import GbmPosHistFile
>>> # get the spacecraft frame from the position history file
>>> filepath = data_path.joinpath('fermi-gbm/glg_poshist_all_170101_v01.fit')
>>> with GbmPosHistFile(filepath) as poshist:
>>>     frame = poshist.get_spacecraft_frame()

>>> earthplot.add_spacecraft_frame(frame, tstart=frame.obstime[0], tstop=5000.,
>>>                                trigtime=frame.obstime[4000], marker='*')

What we did here was specified a time range that began at the start of the file (frame.obstime[0]) and stop time that extends 5,000 seconds from the start time. We also set trigtime=frame.obstime[4000], which means that we set our time of interest to be at that particular time. Since Fermi GBM provides the frame sampling at 1 Hz, this means that we set our time of interest at 4,000 seconds after the start time. Finally, we told Matplotlib we wanted our spacecraft marker to be a star (marker='*').

The resulting plot has a very small black star, so we probably want to make it bigger. You can access that plot element, which is an EarthPoints object:

>>> earthplot.spacecraft
<EarthPoints: 1 points;
              color='black';
              alpha=1.0>

We can make the spacecraft marker larger, change the color, and bring it to the front:

>>> earthplot.spacecraft.sizes = 200
>>> earthplot.spacecraft.color = 'green'
>>> earthplot.spacecraft.zorder = 5

Similarly, the orbital plot element, am EarthLine object, can be accessed:

>>> earthplot.orbit
<EarthLine: color=black;
            alpha=0.4;
            linestyle='-';
            linewidth=5.0>

And we can also update the plot settings for the orbit:

>>> earthplot.orbit.linestyle = '--'
>>> earthplot.orbit.linewidth = 3
>>> earthplot.orbit.color = 'green'

Finally, we can a simple title to the plot that lists the coordinates for the spacecraft position:

>>> earthplot.standard_title()

Reference/API

gdt.core.plot.earthplot Module

Classes

EarthPlot([lat_range, lon_range, saa])

Class for plotting the Earth, primarily related to a spacecraft's position in orbit.

Class Inheritance Diagram