When two or more receivers observe the same satellite constellation simultaneously, a set of correlated vectors are created between the coobserving stations. Most GPS practitioners use more than two receivers. Therefore, most electronic tracking device networks consist of many sets of correlated vectors for every separate session. The longest baselines between stations on the earth are usually relatively short when compared with the 20,000-km distances from the receivers to the GPS satellites. Therefore, even when several receivers are set up on widely spaced stations, as long as they collect their data simultaneously from the same constellation of satellites, they will record very similar errors. In other words, their vectors will be correlated. It is the simultaneity of observation and the resulting correlation of the carrier phase observables that make the extraordinary GPS accuracies possible. Biases that are correlated linearly can be virtually eliminated by differencing the data sets of a session.
In creating an observation, schedule consideration might be given to observing a particular station during a session when none of the satellites would be blocked by obstructions. And while GPS is not restricted by inclement weather, particular access routes may not be so immune. Despite best efforts, a planned observation may have been unsuccessful at a required station on a previous day, and it may need to be revisited. However, the line-of-sight between a particular station and another in the survey is not likely to affect the motorcycle GPS tracker observation schedule, though such a consideration may be critical in a conventional survey. The simplicity of the zero baseline test is an advantage. It is not dependent on special software or a test network and it can be used to separate receiver difficulties from antenna errors. Two or more receivers are connected to one antenna with a signal or antenna splitter.
Rubbings are performed with paper held on top of the monument’s disk; a pencil is run over it in a zigzag pattern producing a positive image of the stamping. This method is a bit more awkward than simply copying the information from the disk onto the data sheet, but it does have the advantage of ensuring the station was actually visited and that the stamping was faithfully recorded. Such rubbings or closeup photographs are required by the provisional FGCC Geometric Geodetic Accuracy Standards and Specifications for Using vehicle GPS tracker Relative Positioning Techniques for all orders of GPS surveys.
The station data sheet is often an important bridge between on-site reconnaissance and the actual occupation of a monument. Neatness and clarity, always paramount virtues of good field notes, are of particular interest when the station data sheet is to be later included in the final report to the client. The overriding principle in drafting a station data sheet is to guide succeeding visitors to the station without ambiguity. A GPS Platforms surveyor on the way to observe the position for the first time may be the initial user of a station data sheet. A poorly written document could void an entire session if the observer is unable to locate the monument. A client, later struggling to find a particular monument with an inadequate data sheet, may ultimately question the value of more than the field notes.