globalmapper.GenerateWatershed
==============================

.. currentmodule:: globalmapper
.. py:function:: GenerateWatershed ([GM_LayerHandle_t32] aLayerList, GM_WatershedParams_t aWatershedParms, int aReserved) -> GM_Error_t32, GM_LayerHandle_t32, GM_LayerHandle_t32

    Performs a watershed calculation on the loaded terrain layers, generating a stream network and optionally a set of
    drainage area features for each stream. There is also a way to find ridge lines rather than generating a stream
    network. The returned stream and drainage layers must be closed with
    :doc:`CloseLayer<../load/globalmapper.CloseLayer>` when you are done with them.

    If you would rather find ridge lines rather than a drainage network, pass in the
    GM_Watershed_FindRidgeLines flag in the GM_WatershedParams_t.mFlags parameter. The ridge line calculation is the
    same as a stream calculation on an inverted terrain, so the parameters have basically the same meaning.

    :param [GM_LayerHandle_t32] aLayerList: List of elevation layers to use or None for all
    :param GM_WatershedParams_t aWatershedParms: Parameters for generating watershed
    :param int aReserved: Reserved for later use, must be 0.
    :returns: Error Code
    :rtype: GM_Error_t32
    :return: Created stream layer
    :rtype: GM_LayerHandle_t32
    :return: Created drainage area layer (if created)
    :rtype: GM_LayerHandle_t32