# How to create an iso-surface along an arbitrarily oriented plane?

 Sometimes one needs to create an iso-surface that is arbitrarily oriented in space,i.e. not parallel or perpendicular to any coordinate axis. This is accomplished as follows:1. First determine the direction cosines of the vector perpendicular to the wanted iso-surface. If you know three points on the plane, then it is easy to determine the direction cosines of the vector perpendicular to the plane. Let the points be A B C. The vector cross product of vector AB and vector BC is a vector perpendicular to the plane containing A B and C.2. Under Define->CustomFieldFunctions, create a customfieldfunction: custom_field_function_0 = ax+by+cz Here a, b, c are the direction cosines of the perpendicular vector that you have determined in step 1. x,y,z are Grid->X-coordinate, etc.3. Using the coordinates of one of the points A B or C, calculate the the value of ax+by+cz.4. Make sure that the case is initialized. Solve->Initialize->Initialize5. Go to Surface->Iso-Surface Select Iso-Surface of custom_field_function_0 Under 'value' type the value that you calculated in step 3. above. Click on Create/ApplyThe iso-surface is created.