Magellan MobileMapper - GPS Software User Manual page 91

To log a feature: Means to save the characteristics of a
feature into MobileMapper Pro's memory. The user is in
charge of entering the description of this feature whereas
the receiver is responsible for saving the GPS position(s) it
has determined on this feature.
To describe a feature: Means to give each attribute of the
feature one of the prompted values for this feature.
Feature Library: A file containing all the feature types required
for a given job. (In fact we should say "Feature Type Library".)
Feature Type: An item present in a feature library. Each fea-
ture type is defined by a geometry type, a name, a certain
number of possible attributes and the list of possible values
for each attribute. There are four different geometries in fea-
ture types: point, line, area and grid.
Field: Any area on MobileMapper Pro's screen dedicated to
displaying the value of a parameter. Some fields are user-ed-
itable, some others are not.
Geographic Information System: A system of digital maps,
data analysis software and a database of features, attributes
and geographic locations.
GIS: See Geographic Information System.
Global Positioning System: A system of satellites providing
worldwide coverage for positioning information. Although in-
stalled and maintained by the United States, the broadcast
signals are available to anyone anywhere in the world.
GPS: See Global Positioning System
GPS satellite geometry: The satellite distribution at a given lo-
cation. measured by the PDOP index
GPS signal multipath: Occurs when the GPS signal arrives at
the antenna by a path other than a straight line. Multipath sig-
nals make the receiver think that a GPS satellite is farther
away than it is and the resultant position is inaccurate.
Job file: File containing a feature type library and a collection
of features that grows as you log new features in the field with
this job file open. All the features in the job file necessarily
"originate" from the feature types present in the job file's fea-
ture type library.
Nesting: This word is used to describe a feature that you are
logging whereas another feature is already being logged.
PDOP: Positional Dilution of Precision. An accuracy factor de-
rived from the geometry of the constellation of GPS satellites
used to calculate a position. In general, the more widely dis-
tributed the satellites are in the sky, the greater the accuracy.
In general, PDOPs less than 10 are good.
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