Technical data

Survey Preparation & Execution 37
Surveying
You arrive on a new project site where you need to perform a kinematic
survey. You set up the base station on an existing point with known
coordinates or an arbitrary point where approximately coordinates will be
assigned. You assign a point ID of 0001 to your base point. You drive a PK
into the ground to mark your initialization point. You assign a point ID of 0100
to your initialization point. You then initialize your kinematic survey by first
performing a static survey on your initialization point. Once initialized, you
proceed to position new points using the kinematic mode. You successfully
position 10 points when you suddenly loose lock on satellites due to an
obstruction (the Z-Xtreme receiver will sound an alarm when fewer than 5
satellites are locked). You must now re-initialize your survey.
You can re-initialize the survey by returning to your initialization point (0100)
and observing it once again, but this time your observation needs to be only
10 seconds in duration because this point is now a known point. Your
initialization point is a known point because you successfully performed a
static survey on this point earlier. When you observe your initialization point
the second time, you need to assign it the same point ID as your first
observation (0100). By doing so, the post-processing software will know that
these are observations on the same point.
3. Initialize on-the-fly
When using a dual-frequency GPS system such as the Z-Xtreme, there is no
requirement that initializations be performed while standing still at one
location. It is possible to initialize your kinematic survey while moving about
the project site (thus the term on-the-fly). Initialization times are about the
same as with the static survey method. The advantage of the on-the-fly
method over the static method is that during the 5-minute observation
required to initialize, you can be moving about the project site productively
locating points of interest. The post-processing software will use this data to
initialize and, once initialized, will establish precise positions on the points
observed during the initialization time period. There is a trick to this method
though. You must collect clean data (no loss-of-lock) during the initialization
period, i.e. the first 5 minutes of the observation. If loss-of-lock occurs during
the initialization period, you run the risk of not being able to initialize the
segment of data between the start and the loss-of-lock. Any points observed
during this time period will have poor precision. For this reason, this method
of initialization is best left for project sites where obstructions are a minimum.
Consider a scenario where this method of initialization would be useful:
You have a landfill that you need to topo. Being that the project site is a
landfill, most of the area has no obstructions with the possible exception of
trees along the perimeter. You set up your base station in an open area. You
then set up your rover system. You turn on the rover system immediately. As
you finish your preparation, the rover system is collecting data for initialization
630045.book Page 37 Sunday, February 11, 2001 11:38 AM