geometric correction

CHAPTER 4A. DERMANIS: REMOTE SENSINGest neighbor interpolation (fig. 4.5). If i ≤ I ≤ i + 1 and j ≤ J ≤ j + 1,i.e. the point ( I , J ) falls in the grid cell with vertices ( i , j), ( i , j + 1),( i + 1, j), ( i + 1, j + 1), the 4 distances from the vertices are evaluated22d i , j ( I − i)+ ( J − j)= , (51)22d , j + 1 = ( I − i)+ ( J − j −1)i , (52)221 , j = ( I − i −1)+ ( J − j)di+ , (53)22+ 1 , j + 1 = ( I − i −1)+ ( J − j −1)di , (54)the minimal one is determined, say d p , q and the value is set equal to thatof the nearest (neighboring) grid point V X , Y= VI, J= Vp,q .The nearest neighbor interpolation has the advantage that it assigns to thenew (registered) image pixel values that have been actually observed. Forthis reason it is the only reasonable method to use when image registrationis preceding image classification. In general image registrationshould follow classification, or other image transformations. Its disadvantageis that it produces images, which are not smooth with an obviouspixel-like effect, especially when the pixel size of the original image isdifferent from that of the new image. The pixel size of the new image isequal to that of the target image or map. The difference in pixel size canbe avoided in image-to-map registration by a proper choice of the mapscale. It is though unavoidable in image-to-image registration when thesensor of the original image is different from the sensor of the target image.The above problems of closest neighbor interpolation can be avoided byusing more appropriate interpolation methods, which produce smoothimages, such as the bilinear and the bicubical interpolation.Figure 4-6: The bilinear interpolationThe bilinear interpolation (fig. 4.6) is utilizing only the 4 grid values10