Why does WAsP Engineering fail to read my WAsP contour map?

WEng reads the WAsP contour map and convert it into grid format. This conversions is tricky and sometimes fails, e.g. with a small inconsistency in the contour map. Here are some tips to avoid map conversion errors:

• Check that the vector map is in WAsP ASCII format.
• WEng may fail to read WAsP ASCII vector maps generated by external software. In this case it sometimes helps to import a map in the WAsP Map Editor and save this as a new file, which you then load into WEng.
• Inspect the contour map in the WAsP Maps Editor. Pay attention to the error indicators and correct possible inconsistencies.
• Working with WAsP, it is sometimes recommended to reduce file size of vector maps. One of the methods provided by the WAsP Map Editor is called ‘contour line thinning’, which means that you reduce the number of points in each terrain contour. The resulting file may be perfect for WAsP but cause a crash in the WEng triangulation method. Contours lie close to each other in steep terrain, and if you ‘thin’ them too aggressively the triangles will tend to be elongated. We suspect that this might disturb the triangulation algorithm.

Map good enough for WAsP Engineering calculations?

Recommendations for preparation of WAsP maps are found in the WAsP help file regarding "WAsP best practices and checklist". The WEng flow model is less tolerant with map errors than the WAsP flow model – e.g. beware of crossing elevation contours. Existing maps can be inspected and edited with the WAsP map editor, which has its own help file. The recommendations for the WEng calculation domain settings are:

• In general, extend the domain 100 times hub heights in all directions from all turbine sites. This is needed for accurate local speedup and reliable extreme-wind calculations.
• In coastal areas you may need a larger run up from the sea side to avoid wrap-around effects of the Fourier based flow model.
• The grid resolution should be finer than the hub height. This is necessary for accurate calculation of shear and flow inclination.
• The grid size should be limited to 500-1000 points in each direction, depending on computer memory and CPU capacity. You may have to compromise with this and the above requirements.

NB: Unlike in WAsP, you should avoid having nearly (or fully) identical contour lines on top of each other when working in WEng. The WAsP MapToGrid routine may crash.

Map good enough for Windfarm Assessment Tool calculations?

WAT uses maps to calculate the IEC 61400 complex terrain indicator. For this purpose the grid must

• extend at least 20 hub heights from each turbine site
• have a grid resolution better than one hub height

Thus, the optimal grid extent and resolution in WAT may differ from those in WEng. It may be a good idea to

• save the WEng project
• temporarily change the grid with the WEng domain editor
• right-click on terrain maps | elevation grid and export in Surfer grid format
• reload the original WEng project
• use the optimized grid for the WAT project