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The net design mainly subject to the users' requirement, but outlay, time interval of
observation, type of receiver and the receiver amount, etc also relate to the net design.
In order to satisfy the users' requirement, we should keep the principle as follows
2.2 Graph design of net
The net design mainly subject to the users' requirement, but outlay, time interval of
observation, type of receiver and the receiver amount, etc also relate to the net design.
In order to satisfy the users' requirement, we should keep the principle as follows:
1. GPS net normally forms closed graph by independent observation borders, such as triangle,
polygon or connecting traverse, etc, to add checking conditions and to improve the net
consistency.
2. When designing the net, the net point should be superposition with the original ground net
points. The superposition points are generally no less than three and distribute evenly on the net in
order to ensure the changing parameters between GPS net and local net.
3. GPS net point should be superposition with the level points, and the other points are
normally united--surveyed with level surveying way or the equivalent way. You can also set some
level united--surveying points in order to offer geoid's information.
4. In order to observe and level united survey, we often set GPS net points at a clear and easy
arriving field.
5. We often distribute some well eyeshot azimuth points around GPS net to ensure united
survey direction. The distance from azimuth to observation station should be more than 300
meters.
According to different purpose of GPS surveying, independent observation borders of GPS
net should compose definite geometry graph. The basic graphs are as follows:
1. Triangle net
The triangle in GPS net is composed of independent observation borders, it has strong
geometry structure and well self-checking ability, it can also find out the coarse difference of
result and to share the difference to each baseline with adjustment.
But this net needs a lot of observation, especially when receivers are lacking it will greatly
prolong the observation time. So only when accuracy and security are required very high, and
receivers are more than three, we can use this graph, see fig 2-2.
2. Circle net
Circle net is composed of many loops which are formed of many independent observation
borders. This net is similar with one of the classical surveying-- lead net. Its structure is a little
worse than triangle net. The amount of baselines in closed loop decides the self--checking ability
and consistency. General speaking, the amount of baselines has such limit as follows:
The advantage of circle net is the small workload, good self-checking and consistency. But
the main disadvantage is that the accuracy of indirect-observed border is lower than that of
direct-observed border, and the baseline accuracy of neighbor points distributes unevenly. In field
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