Point source correction

The IEC method to calculate the temperature at any point in the soil uses the exact analytical solution for a line source in an infinte environment in conjunction with Kennelly's hypthesis to account for the fact that a cable environment is semi-infinite in nature.

However, in reality the entire cable acts as the heat source which deforms the isotherms around the cable, especially with proximity to the earth surface. To consider this physical reality, it is assumed that the cable surface forms an isotherm and that one can imagine that the temperature field is built up by a line source which runs parallel to the cable axis at a distance $d_{psc}$ (eccentricity of the cable) closer to the earth surface according to the book 'Kabel und Leitungen für Starkstrom' by L. Heinhold, 5th edition 1999 (in German).

This yields to a tiny improvement in the ‰ range. Point source correction is optional in Cableizer, and not activated by default.