Within the polygon defined by the closed contour boundary, nodes are generated according to the following principle:

0^th step:

In the 0-th step, a mesh node is generated at all contour points and at all start, end and division points of contour lines (unless a node with these coordinates already exists).

In further steps, points are generated for line contours as follows:

• Points normal to the line contour are generated at contour line division points.

• Additional points are generated at an angle of 90, 150, 210 and 270 degrees to the contour line at the start and end points of l-contours without other neighbouring contour lines.

• Additional points are generated at the start and end points of line contours where further contour sections adjoin, depending on the included or excluded angles. For example, points are generated along the bisecting angles for included angles between 90 and 180 degrees and points are generated normal to both contour sections for angles greater than 270 degrees.

The distance of points generated in these directions from the contour line point is determined from the (possibly average) distance of the contour point to its neighbouring contour line points (dist):

For "normal" contour lines (l-contours), n points are generated at a distance of dist, 2*dist, 3*dist up to n*dist in n generation steps of the boundary node generator (see illustration below).

Boundary node generator for l-contours (step 1)

For fracture contours (k-contours), a point is generated at the maximum distance n*fact*dist from the contour point in n generation steps of the boundary node generator. The scaling factor "fact" (length factor) can be entered by the user. Between this point and the contour point, a predetermined number of additional nodes are generated with exponentially increasing distance to the fracture contour (see figure below).

Boundary node generator for fracture contours (2 additional nodes and factor 0.8; n=2)

In further steps, for point contours with well parameters (R_i, R_a and C>0), points are generated at angles of 45, 90, 135, 180, 225, 270 and 315 degrees with a distance of R_n = R_i * Cⁿ to the contour point.

Nodes are generated starting from a start-, end- or division contour point until one of the following cancellation criteria is met:

The distance reaches the specified limit:

• n*dist for normal line contours (l-contours),

• n*fact*dist for fracture contours (k-contours), and

• the maximum outer radius R_a for p-contours with well parameters, or

• there is already a mesh node in the vicinity of the point to be created, or

• the distance between the point to be created and another base contour line is "too small", or

• the generation direction leads out of the outer contour boundary; in this case, no points are generated in this direction.

Algorithm of the grid node generator