When preparing a design many plans contain elevation data. Various settings in IRRICAD control how elevation data is interpolated and utilised during the design process. The following information will help to understand the effect and use of some of these settings.
Pro Version 11 introduced the ABOS method which is generally faster and better represents likely topography for non-uniform slopes and in situations where elevation data is sparse. Some points to note for this method are:-
Unlike the AEI method there is no limit on the number of contour segments or spot heights that can be processed.
Continuing to simplify contours, during Import Contours, is however desirable as this will improve both general graphical performance and the speed of interpolation.
If this method is used, it may be best to set the “Contour Simplification Tolerance” to a lower value (for example 0.2 m) to ensure that imported contours are reasonably smooth (Settings|Irrigation Items "Contours")
Using the ABOS method means that every elevation, used in a design, is calculated from the DEM grid.
If the "D.E.M. Grid Size" to set to 0 the grid size will be determined automatically so that a reasonable level of accuracy is maintained. Note that in some circumstances this may result in a large grid and consequently interpolation may be slow on low powered machines.
Some other useful tips are:-
ABOS or AEI methods can be selected in Design|Design Parameter|Analysis Parameters "D.E.M. Options". The ABOS method is the default for all new designs.
Regardless of the elevation method used (ABOS or AEI), the grid spans the area covered by elevations. Therefore if the extents of the elevations are much greater than the hydraulic design, care should be taken that effective grid size is sufficient.
Trimming elevations to the extents of the hydraulic design will also increase accuracy as the grid will be finer over the smaller area.
The "Max Error" reported in the "Elevation Limits" dialog is a useful indication if the grid size is acceptable and/or there are some inconsistencies in the elevation data. The top 10 inconsistencies will be listed in the View Errors Report, if any of these errors are significant then the elevation data at the specified location should be checked. Some typical problems with elevation data include: contours crossing or very close together; spot heights inconsistent with neighboring contours or spot heights. If no elevation inconsistencies are found, increase the grid size and re-run.
We hope you have found this helpful. If you have a tip you would like to share, please email your tip to Support@IRRICAD.com