Positional Accuracy Testing of Google Earth

Google Earth provides an open source, easy to access and cost free image data that support map interest community. Therefore, depending of this community on Google Earth, grows up day by day. More than simply providing locational information, Google Earth allows users to add their own content such as photos or descriptions of areas or landmarks. They can also extrapolate information from the satellite imagery obtained by digitizing areas of interest and exporting them for use elsewhere. As such, the application has found a strong following not only in explorers and navigators but also in classrooms all over the world. However, this popularity of Google Earth is not an indication of its accuracy. The aim of this research is to estimate the Google Earth horizontal and vertical accuracy in Khartoum State so as to evaluate this free source of data. This was carried out by comparing Google Earth measured coordinates of points with geodetic Global Positional System (GPS) receiver coordinates over sample of 16 check points located in Khartoum State. Since GPS provide accurate measurement of coordinates on the same ellipsoid as Google Earth, it was used to check the accuracy of Google Earth. Root Mean Square Error (RMSE) was computed for horizontal coordinates and was found to be 1.59m. For height measurement RMSE was computed to be 1.7m. For the research purposes and to pursue the changes occurred while Google Earth images updated, it was noted that the positional accuracy was changed and improved, but the elevation is still as it were before update. Keywords– Google Earth, GPS, Projection, Datum and Positional Accuracy