WHAT IS GPS AND HOW DOES IT WORK?
HOW AND WHY THE COUNTY USES GPS
The County Surveyor and the County Forestry Department both use GPS equipment.
Before GPS, the County Surveyor would have to use conventional equipment (simply put, something to measure angles and distances) to determine bearings and distances between section and quarter corners, also known as Public Land Survey System (PLSS) corners. These bearings and distances, when tied to known coordinates on control points, would be used to determine coordinates on the PLSS corners because once the coordinates of a point are known, the position is known and can always be re-established. Working on roads does not present a real problem with conventional equipment but when these measurements are needed in wooded areas, lines of sight had to be brushed and the work took much longer.
With GPS equipment, the only line of sight required is towards the sky. The GPS equipment receives signals that are broadcast by satellites that are approximately 12,000 miles above the earth. With those signals, the receiver on the ground computes its position. As you can guess, to clear out or find a small open area in the woods is much easier and faster than clearing and brushing miles of line to measure along.
The GPS equipment that the County Surveyor uses is more accurate than measuring with conventional equipment. With conventional equipment, errors accumulate throughout the measurement process and are usually assumed to be uniform and are adjusted “out” throughout the measurement network. This could actually induce errors into previously “good” data. If the measurements aren’t closed to a known point, the potential for errors gets greater the further the points are from known control.
With GPS, any error at a point is an “absolute” error and not related to any other measurements. The survey grade GPS equipment the County Surveyor uses has a published accuracy of approximately 1 centimeter (or less) per point.
The time savings in the measuring process and the accuracy of the equipment make GPS the best choice for the County.
The County Forestry Department uses GPS to update timber stand information, to update and maintain forest trail and road maps, to determine and map boundaries of timber sales and for maintenance of location based features in the geographic information system.
How is GPS (Global Positioning System)data is used in a GIS (Geographic Information System)? In a GIS, all information, whether it be database information, statistics, mapping information or other graphical information, must be spatially related. The spatial relationship occurs when position values in terms of mathematical coordinates are developed and tagged to the other information, usually through relational databases. A GPS unit determines the coordinates of a feature and records the coordinate values of it for use in the GIS. Once this information is in the GIS database, queries can be made on all stored information with meaningful results automatically put into map form.