[GIS] How to assign node IDs to links in a network

arcgis-10.0arcgis-desktoplineNetwork

I have two shapefile layers in ArcGIS for Desktop 10.

I have one line layer and node layer.

My node layer(shp) has a "code_1" field and line layer has a "code_node" field.

The intersection point of the line layer has only one node.

I want get the code from the "code_1" field of the node layer for the line's "code_node" field

For example, for one line, the first node has code_1=1 and the node at the end of line has code_1=2. In this case the code_node attribute in that line must be "12",.

How can I automatically get the code from the nodes for each line?

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Best Answer

Use Feature Vertices To Points to get the START points from the line shapefile. Do the same for END points. Name the resulted layers "start" and "end". Then use Spatial Join to join these resulted layers to your node layer separately (Target features: "start" and "end" layers, Join feature: your node layer, JOIN_ONE_TO_ONE, Match Option: Intersect). Name the resulting layers "startJoin" and "endJoin". Add a new field "origin" to your line layer (with the same properties as your "code_1" field, I suggest TEXT format). Join your line layer to "startJoin" (match FID to ORIG_FID) and by field calculator copy "code_1" in the "origin" field. Add another field "destination" to your line layer and do the same (you may want to remove the existing join before doing this) for "endJoin" and get the "code_1" into "destination" field. Fianlly, do this field calculation to your "code_node" field: [origin]&[destination]

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[GIS] calculate slope for a road network

You probably could do something like this (assuming you already have an elevation raster in the database called 'elev' and the road network is called 'roads' with a primary key 'road_id')

-- Add a column for slope values
ALTER roads ADD COLUMN slope float;

-- Update with: (elevation of start pt - elev of end pt )/length of segment
UPDATE roads SET slope=(
   SELECT ( ST_Value(elev, ST_StartPoint(r.geom))-ST_Value(elev,ST_EndPoint(r.geom))/ST_Length(r.geom) )
   FROM roads AS r
   WHERE r.road_id=roads.road_id);

The ST_Length will, of course return values in the same units as the CRS. If your data is in Lon/Lat degrees, use ST_Length_Spheroid() instead. Slopes going down in the direction of the segments will be positive. Slopes up in the direction of the segment will be negative. Also, the above assumes the elevation units are the same as the CRS units.

HTH

python – Getting Lines and Nodes Around the Confluence Point in a Network System (Line Shapefile)

You work here with a Graph (Graph Theory) and your confluence point is simply a node with a degree (number of edges adjacent to that node) > 2.

As you mentioned a Python tag, a solution in Python with Fiona (for reading the shapefile) and NetworkX (Graph Theory)

The Polylines

Open the shapefile and convert all the segments of the Polylines in egdes of a Graph

import fiona
import networkx as nx
import itertools # for extracting all the line segments
# creation of an undirected Graph
G = nx.Graph()
for line in fiona.open("lines.shp"):
   # convert the line segments to Graph edges
   for seg_start, seg_end in itertools.izip(line['geometry']['coordinates'],line['geometry']['coordinates'][1:]):
       G.add_edge(seg_start, seg_end)

The Graph with Nodes(x) and edges

Now, in NetworkX, the degrees of a node are obtained by degree (I use Shapely here but you can save the resulting shapefiles with Fiona and even Networkx)

from shapely.geometry import Point, LineString
for node in G.nodes_iter():
    if G.degree(node) > 2:
        print Point(node) #the nodes
        for edge in G.edges(node):
            print LineString(edge) # the edges (>2)

Result

You can translate easily the Fiona solution in PyQGIS.

Best Answer

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python – Getting Lines and Nodes Around the Confluence Point in a Network System (Line Shapefile)

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