Overview

GlobalTop GPS module has support for 223 different types of datum. Selecting the right datum type that matches the datum of the map data is important in ensuring the position data received from GPS remains accurate.

Background

A part of equation to the accuracy of GPS positioning is associated with the type of map data used in combination with the GPS receiver. The datum, which defines the shape and size of the earth, is composed from a specific mathematical model with a set of specific geographical reference points. This datum is in turn used as the basis for constructing the map and its coordinates.

Datum is used to translate Earth's three-dimensional sphere into two dimensions ellipsoid (flattened sphere). Contrast to popular beliefs, because the surface of Earth is a highly irregular and the shape itself is not a perfect sphere, for each different location on Earth, there may exists a specific mathematic model that best describes its horizontal coordinates.

In another words, datum affect the positions of Latitude/Longitude and local grid systems. Each datum is associated with a particular reference spheroid that can be different in size, orientation and relative position from the spheroids associated with other datum.

It is important to know the datum type of the map data and set the GPS receiver to the corresponding datum type. If datum is set incorrectly, the position can differ by several hundred meters.

GlobalTop Solution

Currently there are many datum that are in use beside the popular WGS84, such as the Japan standard Tokyo-A and Tokyo-M. GlobalTop GPS modules have support for 223 types of datum to reduce the inaccuracy caused by the deviations of different datum.

All GPS users should be aware of this peculiarity and make sure that your GPS match with the most applicable datum to be used.

Users can select the datum type to be used from our Mini GPS tool available for download from our website, and can also contact us if they wish to set a particular datum as default value via firmware setting.

Requirement

RX pin of module must be connected in order to receive PMTK command using Mini GPS Tool or other terminal program.