Abstract：After having reviewed the basic collocation theory, the principle of the collocation by two minimization steps is introduced. Considering that the stochastic signal contains not only the stochastic information but also some systematic trend, after the systematic trend parameter having been calculated and then the residual was used to compute the covariance function of the stochastic information. With the refitted covariance function, the stochastic signal was evaluated and the systematic trend parameters were estimated again. An actual digital map case shows that the solution accuracy with this method for collocation is better than that with the affine transformation by least squares.
