Section 4: Standards and Specifications
Anchor: #i1000255Standards and Specifications Issues
There are two issues, which are significant within the manuals’ standards and specifications.
First, least squares analysis is the primary process by which the stated project conclusions are justified. However, this process is only valid with sufficient redundancy and correct assumptions made regarding the probability of errors.
Second, the processing of raw GPS observables has been the subject of much innovation and experimentation. This trend is certain to continue, as GPS technology is extremely dynamic and changing constantly.
It is the responsibility of the professional in charge to employ techniques, which are appropriate for the project and to provide verification that the stated conclusions are valid.
The use of these standards and specifications are recommended and do not relieve the surveyor from making decisions or using professional judgment during the course of the field survey and the subsequent data processing to obtain the desired results.
Carefully document the procedures, techniques, and results for every step.
Anchor: #i1000293Accuracy Levels and Specifications
Experience has shown that current receivers and software have the capability to achieve geodetic-quality accuracy levels under certain conditions and restrictions. Specifications for performing control surveys using kinematic techniques require greater observational and occupational redundancies and checks than usually specified by the manufacturers. The specifications provide sufficient observational and occupational redundancy to detect blunders and quantitatively demonstrate accuracy achievement for a survey.
The accuracy reporting requirements of this document are in accordance with accuracy reporting requirements of the Federal Geographic Data Committee’s “Geospatial Positioning Accuracy Standards,” FGDC-STD-007-1998.
Anchor: #i1000308Statistical Analyses
In accordance with new federal positioning standards, these specifications rely heavily on the use of statistical analyses to determine the accuracy of a GPS survey. Regardless of how the observations for a particular survey were obtained, the completed survey must provide the following information:
- elimination or reduction of known and potential systematic error sources
- sufficient occupational and observational redundancy to clearly demonstrate the stated accuracy
- adequate baseline processing and evaluation, network (least squares) adjustment, and data evaluation
- sufficient documentation to allow verification of the results.
Terminology
In dealing with GPS equipment manufacturers, federal agencies and long time surveyors, we find phrases and terminology used in different and confusing ways. For the purpose of this manual, a “GPS observation” is an uninterrupted recording of satellite data at one station and the created file of raw data. A “GPS session” is a number of observations run simultaneously for creating baselines.