Vector Sensor Reference Manual 128
Note - When using a differential correction service, the resultant position may be
referenced to a local datum rather than the WGS-84 ellipsoid. Please refer to your
signal provider for more information.
Post Processing
Post processing is a method to compute accurate positions in post mission by logging raw
measurement data at the base station and the from the rover simultaneously. The differential
processing can then be performed later in the office using sophisticated processing software tools.
There are a small variety of methodologies available to the operator, such as static, rapid static,
kinematic, etc.
Describing in detail the various post processing techniques is beyond the scope of this document,
however, generally, post processing is more complicated from a procedural perspective and
requires more skill to successfully operate than real-time systems.
Real-Time Kinematic (RTK)
Real-Time Kinematic (RTK) is a term used for describing an advanced method of correcting for
GPS errors. The differential method discussed in the previous section is a convention process
How it Works
Similar to conventional DGPS, RTK uses a base station (or a network of base stations) installed at
locations of known coordinates. Measurements in real-time are taken at both the rover and base
station, however, in addition to the C/A code-based range measurement, the carrier phase is also
measured. The additional measurement of the carrier phase is used to compute the number of
carrier cycles between the rover antenna and each of the satellites in view.
Computing the number of cycles to each satellite from the rover antenna is easier said than done,
since both the base and the rover receivers can only measure the portion of the current
wavelength being received (this is the angular carrier phase, measured in degrees from 0 to 360).
This means that the number of full cycles, beyond the portion of the current one being received,
can’t be directly measured in the same manner as the C/A code (through time alignment of a code
copy within the receiver). Some advanced methods of resolving the ambiguous number of carrier
waves to each satellite (called the ambiguity for each satellite) is the job of proprietary algorithms
within capable receivers.
There are two primary types of RTK based upon the type of ambiguity solution that they offer: an
integer (a variable with no fractional wavelength) or a floating variable (a value with that also has a
value beyond the decimal point). A floating integer solution can offer a designer more flexibility,
but it does not provide as much accuracy as a fixed integer ambiguity solution. The Vector Sensor
uses a fixed integer ambiguity solution for computing real-time heading and is able to solve the
To Next Page
Loading...
Need help?
General
