Jochen Schmidt Ian Evans S. Johannes Brinkmann Comparison of polynomial models for land surface curvature calculation. 797-814 2003 17 International Journal of Geographical Information Science 8 http://taylorandfrancis.metapress.com/openurl.asp?genre=article&issn=1365-8816&volume=17&issue=8&spage=797 db/journals/gis/gis17.html#SchmidtSB03