ACCURACY ANALYSIS OF MAPPING BASED ON PHOTOS AND GCPs COLLECTED FROM GOOGLE EARTH

The photoic maps available on Google Earth come primarily from two sources: satellites and aircraft. Google gets this imagery and other digital mapping information from sources such as TeleAtlas and EarthSat, both of which compile photos and maps into digital form for commercial applications. Because the data comes from different sources, it is provided at different resolutions, which is why some areas of the globe appear crisp even at street level while others are blurry from a great distance. The selected test area is located in Egypt. The test area is covered by photos collected from Google Earth with an overlap and side-lap between them ranging between 15%-25%. All GCPs and CPs are collected from Google Earth, based on Universal Transverse Mercator (UTM). The minimum number of GCPs was 5 well distributed GCPs for each photo. Only two ground control points were measured from maps covering the study area on Egyptian Transverse Mercator (ETM). After collecting the required data, the methodology procedures included: firstly, geo-referencing of each photo; secondly, generating a mosaic from the geo-referenced photos; and finally, map conversion from UTM to ETM for the produced mosaic followed by linear transformation using only 2 GCPs measured from maps. In the present research, the accuracy test includes calculations of the discrepancies of (E, N) coordinates for 27 test points (CPs) located on the corrected mosaic. The (E, N) coordinates of check points CPs are compared with the corresponding ones derived from the existing map, which are considered as a reference in this research. The results of this study concluded that the photos of Google Earth can be used successfully for producing maps with suitable scale in similar study area in case of lacking remotely sensed data and field observations. They also concluded that the worries of numerous countries about the level of detail available in the Google Earth must be taken into consideration.