def fromJSON(value):
        """loads the GP object from a JSON string """
        j = json.loads(value)
        v = GPRasterData()
        if "defaultValue" in j:
            v.value = j['defaultValue']
        else:
            v.value = j['value']
        if 'paramName' in j:
            v.paramName = j['paramName']
        elif 'name' in j:
            v.paramName = j['name']
        return v
loads the GP object from a JSON string