Isosurface
An isosurface is a surface made up of points in the Domain volume where the magnitude of a certain quantity takes a constant value. For example, all the points in the Domain where the magnitude of the wind speed is 10m/s forms an isosurface.
For a chosen quantity, it automatically extracts the minimum and maximum values in the entire domain and allows you to specify a value for constructing the isosurface within this range.
One special type of isosurface is always available in Virtualwind: the Terrain Elevation, which defines a surface that every point on this surface has a same (shortest) distance to the terrain surface in your simulation. For instance, you can define an isosurface formed from points that are 20 meters away from the terrain surface. To do this, you can choose an isosurface-based actor, such as Isosurface Isolines, Isosurface Solid Contours, or Isosurface Vectors, and select "QUANTITY_ELEVATION" for the "IsoSurfaceSelection" item in the visulaization tree. Then specify its "Value" subitem to be 20. The following example shows such an isosurface.
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The terrain elevation gives you a convenient way of saying "I want to see what happens 20 meters above the ground" – here ground is actually the terrain surface. If you do not explicitly have a terrain in your simulation, Virtualwind will use the bottom plane of the domain as the default terrain. In this case, the terrain elevation will be identical to orthoslices parallel to the domain's XY plane and the distance is actually the height relative to the bottom plane of the domain – the default ground.