demqgisshortest path
I've got two locations, A and B, and a DTM covering the region between A and B. Say I want to drive from A to B. I want the shortest route possible, but avoiding regions with slopes higher than, let's say 30 degrees.
Can QGIS calculate such a path?
If needed I can also script using python.
There are two choose for you on NAServer. The NAServer is a MapServer object extension that can be used to perform network analysis in a stateless environment using ArcGIS Server.
For publishing a network analysis service you can check out this tutorial...
1.Closest Facility Analysis: displays the best routes between incidents and facilities.
2.OD Cost Matrix: (origin–destination (OD) cost matrix) a table that contains the network impedance from each origin to each destination.
and showing them in a map as openlayers, you can use ArcGIS Server Service.
1.Go to Home > Network(NAServer) > Route
2.Select Solve Route
3.Define your points and barriers
4.Get format as JSON
5.Read json features and add them to vector layer.
example NAServer is here. beside this you have to define stops as following structure:
{
"features" : [
{
"geometry" : {"x" : -122.4079, "y" : 37.78356},
"attributes" : {"Name" : "From", "RouteName" : "Route A"}
},
{
"geometry" : {"x" : -122.404, "y" : 37.782},
"attributes" : {"Name" : "To", "RouteName" : "Route A"}
}
]
}
you can check out this example:
you should know this the link is so long:
_http://sampleserver3.arcgisonline.com/ArcGIS/rest/services/Network/USA/NAServer/Route/solve?stops={+%0D%0A%22features%22++%3A+[%0D%0A{%0D%0A++%22geometry%22+%3A+{%22x%22+%3A+-122.4079%2C+%22y%22+%3A+37.78356}%2C%0D%0A++%22attributes%22+%3A+{%22Name%22+%3A+%22From%22%2C+%22RouteName%22+%3A+%22Route+A%22}%0D%0A}%2C%0D%0A{%0D%0A++%22geometry%22+%3A+{%22x%22+%3A+-122.404%2C+%22y%22+%3A+37.782}%2C%0D%0A++%22attributes%22+%3A+{%22Name%22+%3A+%22To%22%2C+%22RouteName%22+%3A+%22Route+A%22}%0D%0A}%0D%0A]%0D%0A}%0D%0A&barriers=&polylineBarriers=&polygonBarriers=&outSR=4326&ignoreInvalidLocations=true&accumulateAttributeNames=&impedanceAttributeName=Time&restrictionAttributeNames=OneWay%2CTurnRestriction%2CAvoid+passenger+ferries%2CNon-routeable+segments&attributeParameterValues=&restrictUTurns=esriNFSBAllowBacktrack&useHierarchy=true&returnDirections=true&returnRoutes=true&returnStops=false&returnBarriers=false&returnPolylineBarriers=false&returnPolygonBarriers=false&directionsLanguage=en-US&directionsStyleName=NA+Desktop&outputLines=esriNAOutputLineTrueShape&findBestSequence=false&preserveFirstStop=true&preserveLastStop=true&useTimeWindows=true&startTime=1227663551096&outputGeometryPrecision=&outputGeometryPrecisionUnits=esriUnknownUnits&directionsTimeAttributeName=Time&directionsLengthUnits=esriNAUMiles&f=html
The findBestSequence parameter on the RouteParameters class should re-order the stops in the most efficient order (depending on whether you want shortest or fastest route), from the API help :
Find Best Sequence
Gets or sets a value indicating whether the analysis should reorder stops to find the optimized route. The default is false.
Note using this you may wish to preserve the first and/or last stops if that's an origin and destination of the route, e.g.
A.getRouteParameter().setFindBestSequence(true);
A.getRouteParameter().setPreserveFirstStop(true);
Best Answer
There's a python example in the GDAL/OGR Raster Cookbook (look for 'Least Cost Path analysis'). You'll need to install scikit-image for that.
If using QGIS:-
That will find the route with the least overall slope between A and B. The output is a binary raster.
It won't necessarily be the shortest path distance-wise, but it would represent the easiest route between A and B (for example, for hillwalkers or cyclists)