Assessment of Positional Accuracy of Google Earth Imagery: A Case of Adama city

Abstract

Google Earth (GE) is the most popular virtual globe in use today. Given its popularity and usefulness, most users do not pay close attention to the positional accuracy of the imagery, and there is limited information on the subject. This study therefore evaluates the horizontal accuracy of historical Google Earth imagery at two epochs between year 2013 and 2023, and the vertical accuracy of its elevation data within Adama city. The horizontal accuracies of the images were evaluated by comparison with Global Position System coordinate which measured by former name of Ethiopian Mapping Agency (currently known as Institute of Geo-Spatial Science) and the vertical accuracy was also assessed by comparison with a network of 142 Ground Control Points. To mark elevation data of Google Earth, first Ground Control Points were converted into Keyhole Markup Language data format, then open it Google Earth pro, mark the perspective points of Google Earth and save folder of GE marked data. After that the data was converted into feature using GIS software. To generate Z value of Google Earth Advanced Land Observation Satellite (ALOS) Digital Elevation Model was downloaded and imported into GIS software and Z was generated. The positional accuracy for both horizontal and vertical was performed. The latest or recent Google Earth imagery (year 2023) was the most accurate than Google Earth imagery of 2023. The horizontal Root Mean Square Error of Google Earth imagery of 2013 was estimated 5.98846m and 3.9154m in 2023. Vertical positional accuracy of Google Earth was estimated at a value of 15.97m. The estimated Root Mean Square Error of Google Earth was found fit to produce a class-1 map of having scale of 1:20000 as recommended by ASPRS-1990. Also the positional accuracy of Google Earth was seen improving.