TUFLOW HR Output: Difference between revisions
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=Introduction=
High-Resolution (HR) Grid/Raster Map Outputs was first introduced in TUFLOW 2020-10-AB release. When an SGS model uses “<font color="blue"><tt>SGS Approach </tt></font> <font color="red"><tt>== </tt></font> <font color="black"><tt>Method C</tt></font>”, the sampled elevations are retained at the end of the geometry processing. These sub-grid elevations include topography modifiers such as breaklines, and they allow a high-resolution elevation check file to be written and used for high-resolution depth map outputs. Currently, ASC, FLT and TIF raster formats are supported.
Example models with high-resolution outputs are available in the <u>[[TUFLOW_Example_Models|TUFLOW Example Models]]</u> dataset.
For the HR output, the water level at each HR output location is interpolated from the computed 2D water levels (see <u>[[#Water_Level_Interpolation_Methods|Water Level Interpolation Methods]]</u> for details). The depth output is calculated differently for standard and high-resolution outputs:
:* Standard depth output: The depth is calculated at cell centres and corners first, then interpolated to the standard output grid locations (default is half the cell size). This is shown in the image on the left.
:* High-resolution depth output: The depth is the difference between the interpolated water level and the sub-grid elevation. This is shown in the image on the right.<br>
<br>
[[File:Sgs_std_output.png|360px]] [[File:Sgs_hr_output.png|360px]]
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Note that when these two methods are applied, the interpolated corner water level is biased to the non-sheet flow cells, and consequently, sheet flow cells may appear as “dry” cells. The improved approach takes into account that the sheet flow water level is currently under development.
Whilst Methods B and C can substantially improve the water surface mapping of SGS models using direct rainfall (rain-on-grid), there will always be inaccuracies with mapping at a higher resolution than the 2D cell resolution due to interpolation and extrapolation. Regardless of the software, the greater the ratio of 2D cell size to the high-resolution DEM cell size, the greater the potential for mapping inaccuracies. Should better mapping accuracy be required, reducing the 2D cell size to compute the spatial variation in water surface and velocities more accurately is by far the best course of action.
=Interpolation near Thin Breaklines =
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