A priori horizontal displacement (HD) estimation of hydrological features when versioned DEMs are used

Often, in hydrological processes, different (versioned) DEMs of the same area can provide similar results. An example of a versioned DEM can be one that has a different cell size from the original one, or the same cell size but height values that have undergone a generalization process such as smoothing techniques or two DEMs built for different cartographic agencies. Most of the studies present planimetric differences between versioned DEMs only in visual form. These studies graphically compare the differences between the contours as an effect of the different accuracy between two versioned DEMs. However, visual methodology does not enable measurement of how much a contour is horizontally displaced from one DEM to another. If a measure could estimate such displacement, it could be used as an estimation of expected displacement of those hydrological features derived from different versioned DEMs. In this paper, we develop an algorithm to estimate such a measure by automatically calculating the area within two homologous contours present in two different DEMs. The automation process is not easy because homologous contours are not linked by a bijective function. To solve this problem, we use polygon Boolean operations. We observe that the horizontal displacement measure from contours, after the fitting process, can, with a low error, predict the horizontal displacement of streams.