Given a starting point and a travel time, I would like to produce a travel distance polygon. Can I request this from osm2po via http?
What kind of polygons are you thinking of? ConvexHull, Alphashapes, IsoLines? ... osm2po returns either a cloud of visited vertexes or the convex hull. Here is the exact copy from the osm2po-online-help-page:
It is possible to calculate a route in osm2po, output the result as GeoJson and to add it as a layer in QuantumGIS. * Convert the graph file with [cmd=g] and start osm2po with [cmd=r] (Service) * If you need the street-types (-class) enable them by setting [graph.support.edgeflags=true] either in the osm2po.config file or as additional parameter on the commandline. * Instead of opening the WebGUI in your Browser with e.g. [http://localhost:8888/Osm2poService] add these Parameters to the address above [?cmd=fr&source=100&target=1000&format=geojson] * The Browser should show you the routing result as plain text in geojson format (UTF8). * If this works, copy the complete address, open your QuantumGIS and add the layer under [Menu-Layers-Add_VectorLayer] A Dialog opens. Set the [protocol] to [GeoJSON] and the [Encoding] to [UTF8] Finally paste the address into the [URI] Field and click [Open] * The same works with driving circle distance. Here osm2po creates a cloud of points (in geojson-format) which are reachable in either time or distance from a given starting point (source). e.g.: 1) Show each point which can be reached within a distance of 5 km from starting point (53.5,10.0): [?cmd=fx&source=53.5,10.0&findShortestPath=true&maxCost=5.0&format=geojson] 2) Show each point which can be reached within a distance of 12 Minutes (0.2 hours) from starting point (53.5,10.0). [?cmd=fx&source=53.5,10.0&findShortestPath=false&maxCost=0.2&format=geojson]
cmd=fx returns the cloud of points. Replace it with
cmd=fh to receive the hull.