GIS applications

Geographical Information Systems, GIS, is the new buzz word … these are systems that add location based services to a digital map. Basically anything that superimposes services with precise location over a map is a GIS and some are quite amazing!

Basically a GIS presents location bbased information over relevant cartography. Different service providers, public and private, want to know where their physical elements are over a digital map. They also want to be able to know where other relevant physical elements are also marked; gas mains, water pipes, etc so that conflicts can be avoided without inconveniencing customers unnecessarily.

When a service provider wants to create GIS information they have to use GPS technology to gather all the coordinates of all the different elements; power lines, power pilons, water treatment plants, transformers, etc. Once these coordinates are gathered by mobile GPS devices they have to be properly placed in a digital map in the same coordinates!!

This last point is very important. Simply using GPS technology does not guarantee that coordinates will make sense over any map or over time. In other word coordinates taken at the same time of several elements may not exactly match depending on many local conditions. Also coordinates taken of different elements over a period of days will also likely not match. The problem is that there is a certain uncertainty in GPS coordinates due to multipath environment, atmosphere conditions, constellation geometry, etc.

These facts of Satellite based positioning requires that coordinates need to be corrected by using data from a permanent reference station operating at the same time as the mobile coordinates are being taken. Since we know the reference station coordinates, and provided the reference station is not too far away from the field work taking place we can correct the field coordinates to put them in the same reference system as the reference station.

This method guarantees that field measurements can be shared and placed correctly with other similar measurements on digital cartography without having expensive correction campaign for each set of field measurements.

Happy positioning!!
Ignacio Romero

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