Isosurface

The user may also be interested in finding points that fulfil a certain condition, e.g. what volume is fully saturated, or where confining rock layers are. Such a query would split up space into two volumes that can be shown by only drawing the surface separating them. Such a surface can always be considered an isosurface of a value, as it shows answers to questions like where contaminant concentration over a given value is, or where the hydraulic potential exactly zero is. For an isosurface it is obviously insufficient to know the values only at the nodes, we have to use interpolation similar to the cross-section case. Via interpolation it is easy to find where the surface would intersect the edges, and display the polygons making up the surface in every element. Colour coding of the value naturally has little relevance here, as long as it is not the value some different variable. It is useful, for instance, to show saturation values along a layer boundary, which can also be considered to be an isosurface, namely the isosurface of the layer identifiers assigned to the nodes.