White functions on the basis of equal-slope method are established, and value range of pollutants in white function is expanded with full use of information.

Tracing algorithm of equislope curves on free-form surface;

The method of equivalency slope circularity approaching was presented for this.

we compared isogradient obscure clustering method and isogenyv point obscure clustering method in the water environmental quality assessment of Nandujiang River the authors discuss the difference between the methods and point out that the isogeny point obscure clustering method is more practicable than isogradient obscure clustering method in handling weighting.