Lecture notes - Belépés
13. Volume computation
13.5. Using digital terrain models
It is typical that you have to calculate the amount of excavation works between two different states in time of the same area. You have to survey the terrain in both cases and to develop digital terrain models. Therefore the job is comparing two digital terrain models.
The first option is to derive grid models from both DTMs, of course using the same grid points. You have two different elevations at each grid points, the first one comes from the first survey and DTM, the second elevation comes from the second survey and DTM. You can calculate the difference between the two elevations, pay attention to the sign. To put it another way, separate cut and fill works. The total volume can be calculated by applying the grid method.
The second option is to derive cross-sections of both DTMs and compute the difference of areas in each section. Again pay attention to the sign. The total volume can be calculated by applying the cross-section method.
The third option is to compute the difference between the two DTMs. Get the points in the first model and calculate the elevation in its points but having the second model by applying linear interpolation. Then compute the difference between the elevations in the first model and the elevations interpolated along with the second one. Sometimes the two models are swapped and the calculations are repeated. The difference between the models is treated as a new DTM, of course, elevations can be both positive and negatíve.