Horizontal accuracy assessment of very high resolution Google Earth images in the city of Rome,Italy

Google Earth(GE)has recently become the focus of increasing interest and popularity among available online virtual globes used in scientific research projects,due to the free and easily accessed satellite imagery provided with global coverage.Nevertheless,the uses of this service raises several research questions on the quality and uncertainty of spatial data(e.g.positional accuracy,precision,consistency),with implications for potential uses like data collection and validation.This paper aims to analyze the horizontal accuracy of very high resolution(VHR)GE images in the city of Rome(Italy)for the years 2007,2011,and 2013.The evaluation was conducted by using both Global Positioning System ground truth data and cadastral photogrammetric vertex as independent check points.The validation process includes the comparison of histograms,graph plots,tests of normality,azimuthal direction errors,and the calculation of standard statistical parameters.The results show that GE VHR imageries of Rome have an overall positional accuracy close to 1 m,sufficient for deriving ground truth samples,measurements,and large-scale planimetric maps.