Revision as of 15:59, 8 January 2021 view source Pavlina Monhartova (talk \| contribs) Bureaucrats, Administrators 5,368 edits →Do I need to use "SXL" option for pits and why my model is causing "pit inlet level" error? ← Older edit		Revision as of 16:39, 25 January 2021 view source Pavlina Monhartova (talk \| contribs) Bureaucrats, Administrators 5,368 edits No edit summary Newer edit →
Line 10: =Should the same model using Quadtree with smaller cell count always be faster than HPC?= Not necessarily. By default, running a model with a single level Quadtree mesh identical to a HPC grid is always slower, on average 20%. Quadtree really starts to have major benefits once there is at least three levels of cell size and judicious refinement resulting in 80% of cell count reduction. There is one major benefit of Quadtree regardless in that in nearly always has a much smaller GPU RAM memory footprint because unused 2D cells within the bounding rectangle used by a HPC grid are not stored in memory whereas for a grid they are. =When should I not use SGS?= There is a threshold beyond which SGS isn’t required. The benefit of SGS is focussed on cells with variety of elevations within each cell. For flat cells, where all SGS sample points have almost the same elevation, there won’t be much of a difference in comparison without SGS. =When should I not use Quadtree?= Line 15 ⟶ 18: =When should I not use a combination of SGS and Quadtree?= Based on the benchmarking thus far there seems to be little reason not to use SGS with Quadtree. The one exception is if the underlying resolution of the DEM is of similar (or coarser) resolution to the 2D cells then there is little reason to use SGS as there is no detailed sub-cell terrain to sample. SGS was not made the default in the 2020-01 release because for some models, especially those with coarse cell sizes over highly variable terrain, you can see substantially different results due to SGS picking up a lot more detail of the terrain within a 2D cell. Using Quadtree with SGS, and by using coarser cells within your model than you would have using a HPC grid, you will achieve a much better result and good results convergence (as discussed further above). It's highly likely that SGS will be made the default in a future release once there has been extensive industry benchmarking demonstrating using SGS to be consistently superior to not using (which is the case thus far). =The resolution of my underlying DEM is 1m and my 2D cell size is 1m. Is there any benefit in using SGS?=

Quadtree and Sub-Grid Sampling FAQ: Difference between revisions