I am trying to create a contour file for the globe for a project and am using open source GIS software packages. I was trained for several years on ArcGIS and there is a tool to create contours with barriers allowing the user to provide a vector file of "barriers" and create contours with these in mind. In my case I am looking for the open source alternative using QGIS, SAGA, GvSIG, GRASS. I have tried creating a mask in grass and applying the contour function to my DEM without any successful results.
here is a link to the tool description: http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//009z000000tv000000.htm
This is my first post, please forgive me if I have left any vital information out.