Tips for using GPS devices
There are several things to keep in mind when you're using the GPS device to collect information for agronomic uses with GeoAgro GIS.
It is best not convert from one coordinate system to another. Since GeoAgro GIS works with geographic coordinates is always advisable to configure your GPS device to use a geographic coordinate system using the WGS84 Datum.
GeoAgro GIS works with Geographic Coordinate System and Datum WGS84. So, it's advisable to Setup the GPS reference system to WGS 84.
The accuracy of the GPS coordinate readings are dependent of the time being over the location and the quantity and quality of the satellite signals. Most GPS receivers can report a theoretical horizontal accuracy based on local conditions at the time of reading. In Personal Garmin devices this is done on the Satellite Page. To access it select Satellites in the Main Menu. The display will show the current accuracy of measurement, a theoretical precision in the order of 7ft to 10ft will do.
If you're taking notes on paper, it's recommended to set the position format in decimal degrees. A measurement in decimal degrees to five decimal places is more precise than a measurement in degrees, minutes and seconds
Taking points accurately
It is very important to be careful when surveying data (especially the corner points of fields), as errors committed in this stage will affect future operations. Is essential to take the points exactly where they should be represented. In the image below is displayed the correct way to locate the GPS receiver at reading time to mark the corner of a farm/field (taking into account previous recommendations).
Number of points
The number of points needed to delineate a Farm or Field depends largely on the shape and extension. For example, a regular rectangular field may require 4 points. Instead, an irregular lot bordering a stream will require more nodes to correctly represent it.
Identifying downloaded GPS data
After you download GPS data to GeoAgro GIS, you may find that it's not easy to identify the downloaded points. Please take into account the following considerations when trying to import points from the GPS device:
- It is convenient to use some type of standard nomenclature for naming the gps points or 'waypoints' as you survey them. For example: If you are surveying the corners of a field '11b' you could use the name of plus a sequential number, so the points would be called 11b-01, 11b-02, etc.
- It is advisable to clear all GPS data once you've downloaded it, this will avoid repeating downloads in the future and having to search between data from different surveys.