Use a General Projection nonlocal coupling () to define integration along curves. A projection coupling operator evaluates an expression defined on a source by integration along lines or curves depending on the evaluation point in the destination. The General Projection operator is defined by mapping the source to an abstract intermediate space of dimension srcedim, and the destination to the subspace of dimension srcedim−1 obtained by setting the last coordinate to 0 (srcedim is the dimension of the source selection). To every point in the destination, there is a vertical line in the intermediate space, obtained by allowing the last coordinate to vary while the remaining coordinates are given by the destination map. The set of points in the source selection that are mapped onto this line by the source map is a line or curve, and the projection operator is evaluated by integrating along this line or curve. The default Operator name is genproj1.

Specify the general projection source map using expressions in the x-expression, y-expression, and z-expression fields.

Use expressions containing spatial coordinates in the source geometry when defining the map. The map must be approximately linear within each mesh element. Select a Source frame from the list.

Enter an x-expression and, depending on the dimensions, y-expression for each coordinate except the last in the intermediate space.

Enter an Integration order of the numerical integration method (default: 4). See integration order in the Glossary.