EPSG guidance note #7-2, http://www.epsg.org 2017-06-13 true false false For transformation Belge Lambert 72 to ED50 / UTM zone 31N, Eo1 = 0 No1 = 0 Eo2 = 449681.702 No2 = 5460505.326 A1 = -71.3747 A2 = 1858.8407 A3 = -5.4504 A4 = -16.9681 A5 = 4.0783 A6 = 0.2193 For source coordinate system E1=200000 N1=100000, then E2 = 647737.377 N2 = 5564124.227. urn:ogc:def:method:EPSG::9652 Complex polynomial of degree 3 Coordinate pairs treated as complex numbers. This exploits the correlation between the polynomial coefficients and leads to a smaller number of coefficients than the general polynomial of degree 3. 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. The relationship between two projected coordinate reference systems may be approximated more elegantly by a single polynomial regression formula written in terms of complex numbers. The advantage is that the dependence between the ‘A’ and ‘B’ coefficients (for U and V) is taken into account in the formula, resulting in fewer coefficients for the same order polynomial. A third-order polynomial in complex numbers is used in Belgium. mT.(dX + i. dY) = (A1 + i. A2).(U + i.V) + (A3 + i. A4).(U + i.V)^2 + (A5 + i. A6).(U + i.V)^3 where U = mS.(XS - XS0) V = mS.(YS - YS0) and mS, mT are the scaling factors for the coordinate differences in the source and target coordinate reference systems. The polynomial to degree 4 can alternatively be expressed in matrix form. Then XT = XS - XS0 + XT0 + dX YT = YS - YS0 + YT0 + dY where XT , YT are coordinates in the target coordinate reference system, XS , YS are coordinates in the source coordinate reference system, XS0 , YS0 are coordinates of the evaluation point in the source coordinate reference system, XT0 , YT0 are coordinates of the evaluation point in the target coordinate reference system. Note that the zero order coefficients of the general polynomial, A0 and B0, have apparently disappeared. In reality they are absorbed by the different coordinates of the source and of the target evaluation point, which in this case, are numerically very different because of the use of two different projected coordinate reference systems for source and target. The transformation parameter values (the coefficients) are not reversible. For the reverse transformation a different set of parameter values are required, used within the same formulas as the forward direction.