Technical data

38 Post-Process GPS Surveying
on some arbitrary location. After two minutes, you are ready to begin locating
topo points. You decide to start at the northeast corner of the landfill because
it is wide open with no obstructions. It takes you approximately 1 minute to
walk to the location of the first topo shot. By this time, you have already
collected 3 minutes of data that will be used towards your initialization. You
begin collecting topo points. In the next 2 minutes, you have collected 4 topo
points without lose-of-lock. By this time, the system has collected 5 minutes
of data, enough to initialize. Without hesitation, you continue with your
survey.
When this data is processed, the kinematic survey will initialize using the data
collected during the start of the survey. Even points collected prior to
initialization will result in precise positions.
You successfully continue to collect topo points for approximately 30 minutes
without loss-of-lock. You now are in the perimeter areas were there are trees
close to the edge of the landfill. While attempting to locate topo points right
on the edge of the trees, the kinematic alarm in the receiver sounds indicating
that you have loss your initialization. You must now re-initialize. It is good
practice to establish a re-initialization point near an area where you think you
may loose lock. This is done by simply driving a PK into the ground and
observing this point prior to entering into the obstructed area. If lose-of-lock
occurs, you can simply observe the re-initialization point for 10 seconds to
regain initialization. As an alternative, once you loose lock, you can move out
of the obstructed area and collect data on other points where there are no
obstructions for approximately 5 minutes, giving the system enough clean
data to re-initialize. Then move back into the obstructed area to collect more
points.
On-the-fly initialization is an effective method for initializing your kinematic survey
since there is no time wasted waiting for the system to initialize. But, you must be
careful that you collect clean data during the initialization period or you run the risk
of getting poor positions on some of your points.
Point Observation
When initialized, all data collected by the rover system will produce centimeter-level
results. Whether walking around the project area or positioned over a feature, every
data sample stored in memory will produce a centimeter-level position. If your
recording interval is set to 2 seconds, data samples are written to memory every 2
seconds, all of which are processed by the post-processing software to generate
centimeter-level positions. If you are walking around the project site, a position is
calculated every 2 seconds producing a crumb-trail of where you walked. If you
stop and observe a feature of interest for 10 seconds, five data samples are
observed for this feature, producing a more precise position than those produced
630045.book Page 38 Sunday, February 11, 2001 11:38 AM