Technical data

26 Post-Process GPS Surveying
4. Ensure that each operator of a GPS receiver has blank GPS observation logs
to utilize during data collection. Fill out one sheet for each observation of
each point. Observation logs will be discussed in more detail later in this
section. The post-processing software supports the ability to print blank
observation logs for use during data collection.
With the previous checklist completed, field data collection can begin.
When collecting data using the Static method, each Z-Xtreme receiver will follow
precisely the same steps in equipment setup and survey execution. These steps
are presented below.
1. Determine if point location is suitable for GPS observations
As discussed earlier, obstructions between the GPS antenna and the GPS
satellites interfere with data collection. The best results are obtains while
observing points that have clear view to the sky. When obstructions are
present, observation times need to increase to obtain the same level of
accuracy. With enough obstructions, it becomes impossible to obtain enough
quality data to determine an accurate position for the point.
If the exact location of the point to be surveyed is flexible, select a location
that contains the least amount of obstructions. If the location is not flexible
and is obstructed, extend the observation time for the point. With a severely
obstructed point, it may be necessary to observe a pair of points offset from
the point of interest. The position of the point of interest can later be
established through conventional means using the offset points.
Determining if a location is suitable for GPS observations is far from an exact
science. Successes and failures will eventually give a user a feel for the
suitability of a location.
2. Position GPS antenna over point to be surveyed
The GPS antenna is the data collection point for GPS observations, i.e. the
computed position for the point will be the location of the GPS antenna.
Therefore, it must be precisely positioned over the point to be surveyed. The
two most common mounts for the receiver antenna are a conventional tripod
and a fixed height GPS tripod (Figure 4.3). Either is sufficient for the task but
the fixed height tripod is recommended since it eliminates the possibility of
incorrectly determining the instrument height of the antenna.
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