Transformation from ITRF2000 to WGS84 – A Case Study for Iranian Permanent GPS Network, IPGN





The Molodensky-Badekas model:
The Molodensky-Badekas model (Molodensky et al., 1962; Badekas, 1969) is also a seven-parameter conformal transformation of three-dimensional Cartesian co-ordinates between datums, but is more suited to the transformation between terrestrial and satellite datums (Krakiwsky and Thomson, 1974). The Molodensky-Badekas model, as given by Krakiwsky and Thomson (1974), Burford (1985) and Harvey (1986), is
to the Bursa-Wolf model. Therefore, the only conceptual difference between the Molodensky-Badekas and Bursa-Wolf models is the choice of the point about which the axial rotations and scale change are applied. As this point is the barycentre for the Molodensky-Badekas model, this model offers a more appropriate option for the transformation between terrestrial and satellite datums. Theoretically, the Bursa-Wolf and Molodensky-Badekas models should give the same results when the same data are used to determine the respective sets of transformation parameters (Harvey, 1986).



However, due to better results, in this region, the Bursa-Wolf was used for determination the transformation parameters.

Transformation
First step in this process was selecting some stations if IPGN of which WGS coordinates were available and also have suitable distribution in Iran(fig5).These stations should have been stable enough to trust. The two transformation models were tested on these stations in order to find best transformation parameters. According to the results, Bursa-Wolf was better.


Figure 5: Selected stations in the first step



Figure 6: Residuals of selected stations in the first step