Borehold trajectory between two consecutive survey points is approximated by using a curve defined in three dimensional space. Mathematically, this curve is envisioned to be the course swept by the end points of the vectors originating from the wellhead. These vectors are represented by a single vector function. Three components of the vector function are defined as a second degree polynomical function of the measured depth (MD). These second degree functions represent the change in North-South, East-West, and the true vertical depth (TVD) co-ordinates of any point on the well course. The second degree polynomical relation is verified by using the data from a small scale curved hole model measurements as well as the data from the field measurements.