Hi Johannes, For more complex network analysis I can warmly recommend the igraph package (http://igraph.org/, which has both Python and R bindings). It comes very handy for customized network analysis, is not too complicated to learn, well documented and quite efficient. I could provide you with some sample code in R if that would be of interest.
Cheers Stefan From: grass-user-boun...@lists.osgeo.org [mailto:grass-user-boun...@lists.osgeo.org] On Behalf Of Johannes Radinger Sent: 18. mars 2015 10:30 To: GRASS user list Subject: [GRASS-user] Stream order for vector networks Hi, I am interested in calculating stream order (Strahler, Shreve) for stream networks based on GRASS vector networks (e.g. created by v.net<http://v.net>) without using the raster approach of the GRASS add-on r.stream.order. Therefore, I came across following paper: Gleyzer, A., Denisyuk, M., Rimmer, A. and Salingar, Y. (2004), A FAST RECURSIVE GIS ALGORITHM FOR COMPUTING STRAHLER STREAM ORDER IN BRAIDED AND NONBRAIDED NETWORKS. JAWRA Journal of the American Water Resources Association, 40: 937–946. doi: 10.1111/j.1752-1688.2004.tb01057.x which also provides pseudocode to calculate Strahler order for non-braided and braided vector networks defined by arcs and nodes. Thus, I am wondering if it is possible to get the information from which node a specific arc starts (from_node) and where it drains to (to_node). BTW, I seems some kind of this information is already provided with the NC-dataset (FNODE_ and TNODE column) in the streams attribute table, however I don't know where this information comes from. Of course to extract this information the network needs to be directed to define what is the upstream and what the downstream node of each arc. However, having this information available, it should not be to complicated to apply the algorithm proposed by Gleyzer et al 2004. Thus I am interested to get 'from_node' and 'to_node' information e.g. stored in the attribute table of v.net<http://v.net> output? Here the pseudocode provided by Gleyzer et al 2004: ######################################################################## MakeDictionaries(Network) 1 for each Arc ∈ Network 2 do FromNodesPerArc[Arc's ID] ← Arc’s FromNodeID 3 InflowingArcsPerNode[Arc's ToNodeID] ← InflowingArcsPerNode[Arc’s ToNodeID] ∪ Arc’s ID 4 OriginatingNode[Arc's ID] ← Arc’s FromNodeID StreamOrdering(ArcID) 1 Visited[ArcID] ← true 2 if | InflowingArcsPerNode[ FromNodesPerArc[ArcID] ] | = 0 3 then StreamOrders[ArcID] ← 1 4 else 5 for each Arc ∈ InflowingArcsPerNode[ FromNodesPerArc[ArcID] ] 6 do if not Visited[Arc] 7 then UpstreamOrders[Arc] ← (StreamOrdering(Arc), OriginatingNode[Arc]) 8 else UpstreamOrders[Arc] ← (StreamOrders[Arc], OriginatingNode[Arc]) 9 MaxOrder ← 0 10 MaxOrderCount ← 0 11 for each (Order, Origin) ∈ UpstreamOrders 12 do if Order > MaxOrder 13 then MaxOrder ← Order 14 MaxOrderCount ← 1 15 MaxOrderOrigin ← Origin 16 else if Order = MaxOrder 17 then if Origin ≠ MaxOrderOrigin 18 then MaxOrderCount ← MaxOrderCount + 1 19 if MaxOrderCount > 1 20 then StreamOrders[ArcID] ← MaxOrder + 1 21 OriginatingNode[ArcID] ← FromNodesPerArc[ArcID] 22 else StreamOrders[ArcID] ← MaxOrder 23 OriginatingNode[ArcID] ← MaxOrderOrigin 24 if SegmentIDsPerOriginatingNode[ OriginatingNode[ArcID] ] = nil 25 then SegmentIDs[ StreamOrders[ArcID] ] ← SegmentIDs[ StreamOrders[ArcID] ] + 1 26 SegmentIDsPerOriginatingNode[ OriginatingNode[ArcID] ] ← SegmentIDs[ StreamOrders[ArcID] ] 27 Segments[ArcID] ← SegmentIDsPerOriginatingNode[ OriginatingNode[ArcID] ] 28 return StreamOrders[ArcID] ######################################################################## Is there anyone having experience with that, or has already tried to implement a vector-stream order approach in GRASS GIS. Specifically I am interested in Shreve stream order for simple (non-braided) stream networks and Strahler stream order for braided river networks (Gleyzer et al 2004). Best regards, Johannes
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