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Reference systems

December 13 2022

There are thousands of reference systems in the world. For example, the well know geocentric reference system WGS84, used by the Global Positioning System (GPS) is one of them. Others are created for specific countries and regions. Some of them are almost aligned with International Terrestrial Reference Frame (ITRF), they are known as modern datum. Others are a heritage from the past and are needed only when reading old maps and documents.

All GNSS receivers will typically output positions with respect to WGS84. If used in RTK mode, they will output their positions with respect to the datum used by the Base Station (typically a modern datum). WGS84 is not suitable for surveying since it is a time-dependent datum (coordinates are slowly moving with time). It is better to generate positions in a well know and stable reference system.

For sake of simplicity, most mobile applications display positions in WGS84 as output by a GNSS receiver, and require additional transformations to transform these coordinates in a different datum. Making these transformations with another software inevitably takes time, increase complexity, increases the cost and induces errors.

We have designed OnPOZ to be reliable, easy to use and cost efficient. Dealing with reference systems makes no exception. OnPOZ offers the possibility to select the reference system from a list of well-known EPSG Codes. You can also simply click on a map nearby your location to find out all EPSG Codes available in your area. You can also import your own ESRI PRJ files. The limitation with the EPSG codes and PRJ files is the lack of information (7-parameters) to apply datum transformation (from WGS84 to your modern datum).  Typically, users working with GNSS equipment are dealing with modern datum (like NAD83 in North America). For this reason, OnPOZ implemented, within the selection of reference systems, an option to handle all coordinate transformation at the highest accuracy level.  

OnPOZ allows you to align GNSS-WGS84 positions to your modern datum. It is simply set with the OnPOZ Cloud Mapping System edition window.

If you are working in RTK mode, this transformation is not required since RTK corrections allow to output positions perfectly aligned with the reference system used by the Base Station sending RTK corrections. OnPOZ Collect is able to identify if positions are RTK corrected or not, and thus apply the datum correction only if needed.

If you are using a modern datum, there is probably no reason to turn the datum correction off. Even if you do RTK, you probably want to use the datum correction for any position that would not receive an RTK correction.

The OnPOZ Mapping System interface displays if your Mapping Systems use a datum correction (transformation) or not.