= Relief Displacement =

Relief displacement  is the shift in an object's image position caused by its elevation above a particular datum. For vertical or near vertical photography the shift occurs radially from the nadir point. This effect is demonstrated in the diagram below. Though the distances between A-B and C-D are identical on the datum plane, their corresponding representations on the photo plane are not (i.e. distances between a-b and c-d are not equivalent). 

[[Image(relief_displacement.jpg)]]