1. A computer-executed method for converting coordinates for a position of an entity from a first coordinate system to a second coordinate system, comprising: determining by a computer processor whether the coordinates for the position of the entity in the first coordinate system are within a predetermined bound; calculating by the computer processor a value of at least one trigonometric function from a previously-saved value of the at least one trigonometric function using a linear approximation of the at least one trigonometric function when the coordinates for the position of the entity in the first coordinate system are within the predetermined bound; and determining by the computer processor coordinates for the position of the entity in the second coordinate system from the calculated value.