When using GPS, it is important to know how many satellites you are tracking and their position in the sky. Satellite Skyplot's visual and graphical screen aids in identifying when satellites are being masked by surrounding structures, trees and mountains. Satellites close to the horizon, under fifteen degrees, are less helpful resolving the rover position because of extra atmospheric interference. If there are too few satellites present, the receiver will be unable to resolve its position. Typically five satellites are required to resolve position and four are needed to maintain locked solution. Satellite Skyplot can be an invaluable tool to help you monitor the current satellite configuration.
The skyplot screen appears at left. The top half of this window displays the visible satellite information in chart form. PRN is the satellite identification number. Azi is an abbreviation for azimuth; the horizontal angle from due north, in degrees measured clockwise, to the satellite position (0 to 360 degrees). Elv is an abbreviation for elevation; the vertical angle above the horizon where the satellite can be found (0 to 90 degrees). One entry appears for each satellite that the receiver is tracking.
The image on the lower half of the window displays the same information graphically. It shows a map of the sky with North at the top, East to the right. The centerpoint, where the lines cross, is straight up. Each satellite appears as a symbol resembling an "H". As you can see, most of the visible satellites were in the Northeast when this image was captured. The inner circle represents an elevation of sixty degrees. The outer circle is the horizon. Roughly speaking, any "H" touching this circle is too low in the sky to be of much use. For GPS receivers that support GLONAS satellites, Skyplot will show these satellites with a "G" symbol.
For some types of GPS receivers, the receiver will report which
satellites are being used for calculating the position and which
are only being tracked. A satellite might be only tracked and not
part of the solution if the satellite is too low on the horizon or
when the signal is not clear. The skyplot will highlight the
satellites that are part of the calculations.