Note: These formulas have been transcribed from EPSG Guidance Note #7-2. Users are encouraged to use that document rather than the text which follows as reference because limitations in the transcription will be avoided.¶¶First it is necessary to derive ellipsoidal values Po, Lo of the topocentric origin from their geocentric values Xo, Yo, Zo through the reverse formulas given in method 9602.¶¶Then topocentric coordinates [U, V, W] are computed as follows:¶¶U = – (X-Xo) sin Lo + (Y-Yo) cos Lo¶V = – (X–Xo) sin Po cos Lo – (Y–Yo) sin Po sin Lo + (Z–Zo) cos Po¶W = (X–Xo) cos Po cos Lo + (Y–Yo) cos Po sin Lo + (Z–Zo) sin Po ¶¶
The reverse formulas to calculate geocentric coordinates from topocentric coordinates are:¶¶X = Xo – U sin Lo  – V sin Po cos Lo + W cos Po cos Lo¶Y = Yo + U cos Lo – V sin Po sin Lo  + W cos Po sin Lo ¶Z = Zo + V cos Po + W sin Po