An Algorithm to Extract More Accurate Slopes From DEMs

In this letter, a new algorithm Quad is proposed to improve slope accuracy. According to the traditional Horn algorithm, the importance of neighboring cells depends on their distance from the center, but strangely, no consideration is given to the center cell itself. The loss of self-elevation leads to unpredictable distortions, which can cause errors. To make up for this kind of shortfall, the Quad algorithm uses the 2 × 2 cell neighborhood model instead of the 3 × 3 one so that the center cell's own elevation becomes the most important factor during calculation. While the horizontal and vertical cells are twice as important as the corn cell, the center cell gets twice larger than the corn one. The comparison between Horn and Quad is based on three different artificial surfaces, in which we can obtain the true slope value by derivation. Experiments indicate that Quad calculates the slope more accurately, and from the results of Student's t-test, its performance is significantly better than Horn.