The Effect of the Number of Control Points on the Adjusted Satellite Images


By Dr. Nagi Zomrawi Mohammed Yousif, Abuelhassan Ali Idriss Abdalla.


Traditional survey methods become tedious and time consuming and hens very cost with large scale mapping surveys. In recent years remote sensing imagery was adopted to reduce the cost and facilitate the survey works. These images require some control points to match with the ground coordinates. This research work is oriented to study the effect of the number of control points on the adjusted satellite image. Quick bird image was tested utilizing number of control points. These points were selected on the image first and then observed on the ground using GPS receiver. Some control points was used to adjust the image, where the others were used as check points. Satellite image was repeatedly adjusted and then accuracy was estimated. The effect of the number of control points on the adjusted image was examined by increasing the number of control points in georefrencing model and estimating the accuracy in each case. Three geo-referencing models were taken into account in this research .These models were first order polynomial, affine and projective model. First order polynomial and affine models require at least 3 control points to adjust a satellite image, where, 4 control points are required when using projective model. Results showed that the accuracy of the adjusted satellite image was improved with increasing the number of control points. And the projective model yield better accuracy using four control points compared with other tested models. Moreover, six control points were sufficiently enough to adjusted satellite image using first order polynomial model. Also results showed that affine model always provides lower accuracy compared with other tested models.


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