OmniSTAR 5220HP, User Manual

Page: 18 / 83

OmniSTAR 5220HP User Manual
Issue 1.32 12/2010
18
Operating considerations
The 5220HP has proven to be a high-quality positioning device. The accuracy
that the user can obtain depends on several factors, including:
•
Number of visible satellites
•
Multipath
•
Dilution of Precision (DOP)
•
Satellite elevations
•
OmniSTAR corrections
Number of visible satellites
A minimum of four satellites is required to calculate a 3-dimensional position.
In general it can be said that every increase in the number of visible satellites
will result in an increase in the systems’ accuracy. As the GPS satellites orbit
the earth the number of visible satellites will change in time. The GPS
constellation has been designed to provide a minimum of 4 visible satellites at
any location at all times. The number of visible satellites can decrease due to
blockage by objects such as trees and buildings.
Multipath
It is possible for satellite signals to reflect off large nearby objects such as
buildings, cars or even the ground, thereby resulting in an erroneous
distance measurement. This phenomenon is known as multipath. Multipath
can cause significant errors in the position determination and it is therefore
important to place the receiver in an environment, which is free of large
reflective surfaces. It is also recommended to mount the receiver directly
onto a surface, while maintaining a clear view of the sky in all directions
.
Figure 4: Multipath