Global Mapper v25.0

Where does watershed generation start?

JSL Global Mapper UserTrusted User

I was wondering if there is a protocol that the watershed generation algorithm uses to decide which grid cell to begin the slope calculation? For example, if I have a square polygon selected to generate a watershed on, will it begin in the center? Or will it begin with the highest point of elevation?


  • JSL
    JSL Global Mapper User Trusted User

    I reread the Planchon & Darboux (2001) paper on which GM's watershed process is based, and I'm reformulating my question: what I need to know is in what order DEM points are scanned in the watershed generation process. Is it from left to right starting in the upper left corner of the grid, or is it another order?

    I'm working on a research problem using different polygons for watershed generation, and I've found that in DEMs with lots of flat areas, the streamflow varies directly depending upon the geometry of the bounding window. So it is very important for me to know the order in which points are acted upon in the watershed generation process, so I can incorporate that into the research.

    Thanks for any help.