Data Hacking

248 Part III — Data Hacking
Azimuth and Elevation Graphs
This window (see Figure 10-39) enables you to view any satellites that are in view from your
current location (or, more accurately, from the location of the GPS receiver).
FIGURE 10-39: Satellites currently visible
Each satellite is identified by its pseudo-random number (PRN), its azimuth (denoted by the
letter A), and its elevation (denoted by the letter B). This window also enables you to do something
else that is interesting: plot and print the physical mask angle. When you are using your
GPS in a stationary or static application (such as to get the signal for synchronizing your
PC clock), it is important that you place the antenna where it can get a clear view of the sky.
However, sometimes obstructions block the signal from the GPS to the antenna. Knowing the
effect of these obstructions on the tracking of satellites can be essential because there may be
times when the obstruction is adversely affecting reception.
The Azimuth and Elevation window can graphically demonstrate the elevation mask angle. The
mask angle is represented by a blue, jagged line that is built by using satellite information. The
mask angle is, in effect, the “horizon” for the GPS antenna at that point. Using the information
from the SNR (signal to noise ratio) and satellite status, a graphical representation of the mask
angle is created (as shown in Figure 10-40).
It can take up to 24 hours of continuous tracking of satellites to gather all the information
needed to build an accurate mask angle.
If you want more details about satellite availability, along with details about how obstructions will
affect your reception, I suggest you visit www.trimble.com/planningsoftware.html.
Here you can download free software that enables you to calculate satellite availability, create
sky plots of availability, and get information on visible satellites.