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Network Graphs & Solvers REST Tutorial (DC)

The following guide provides step-by-step instructions to get started with using the Network Graphs & Solvers in Kinetica. This guide demonstrates some key graph concepts as well as how to create and solve a graph using the Kinetica REST API.

Prerequisites

Data File

The tutorial makes use of the dc_shape dataset, which can be ingested from the data file mentioned above. To ingest the file using GAdmin:

  1. Navigate to GAdmin and login (http://<kinetica-host>:8080/)
  2. In the top menu, click Data ‣ Import
  3. In the top right corner, click Advanced CSV Import
  4. Click Select File and select the data file from your local directory
  5. Leave the default options and values for the rest of Step 1 and Step 2
  6. Under Step 3: Confirm, click Import CSV

The file will be validated and records will be inserted.

Using the REST API

As mentioned above, running the following examples requires access to a REST client or a terminal. GAdmin contains a REST client (Query ‣ API) into which you can copy and paste JSON, so there's no need to download a third-party REST client. If opting to run the tutorial via a terminal, the tutorial script and cURL package are required. See Tutorial via Terminal for more information.

Key Information and Concepts

After the data file has been ingested into Kinetica, you should learn about the dataset and how it relates to the Network Graphs Solvers.

Data

The dc_shape dataset is a HERE dataset and is analogous to most road network datasets you could find in that it includes columns for the type of road, the average speed, the direction of the road, a WKT linestring for its geographic location, a unique ID integer for the road, and more. The graph used in the example is created with two columns from the dc_shape dataset:

  • shape -- a WKT linestring composed of points that make up various streets, roads, highways, alleyways, and footpaths throughout Washington, D.C.
  • direction -- an integer column that conveys information about the directionality of the road, with forward meaning the direction in which the way is drawn in OSM and backward being the opposite direction:
    • 0 -- a forward one-way road
    • 1 -- a two-way road
    • 2 -- a backward one-way road

You'll notice later that the shape column is also part of an inline calculation for distance as weight during graph creation using the ST_LENGTH and ST_NPOINTS geospatial functions.

Graph Concepts

A graph typically comprises Nodes, Edges, Weights, Restrictions but only requires edges and weights. The graph created in this tutorial only uses edges and weights.

In this particular example, edges are logically mapped to sections of roadways and footpaths throughout the Washington, D.C., area. Each edge corresponds to a consecutive pair of points from each of the source LINESTRINGs, so a LINESTRING containing n points will have n-1 edges. Because the source graph is not created with nodes, implicit nodes are assigned at either end of each edge after graph creation.

For example, link ID 18350083 is a part of the Ward Circle roundabout, which itself is part of Massachusetts Avenue Northwest near American University. Selecting link ID 18350083 from the dc_shape table reveals the following WKT linestring (the end of the linestring was removed for clarity):

LINESTRING (-77.08544159 38.93787003, -77.08544159 38.93793869, -77.08545685 38.9380188, -77.08548737 38.9381218, ...)

As noted above, each consecutive pair of coordinates will correspond to an edge in the graph, e.g.:

  • Edge A - LINESTRING(-77.08544159 38.93787003, -77.08544159 38.93793869)
  • Edge B - LINESTRING(-77.08544159 38.93793869, -77.08545685 38.9380188)
  • Edge C - LINESTRING(-77.08545685 38.9380188, -77.08548737 38.9381218)

Tip

After graph creation (and assuming the graph table was created), you can view each edge's details, including its respective WKT linestring, using WMS and clicking an edge:

../../_images/edge_wms.png

Each coordinate pair composing an edge is an implicit node:

../../_images/edge_wms_nodes.png

Weights in this graph, as mentioned previously, are an abstract cost (distance, time, etc.) for travelling any roadway or footpath in the Washington, D.C., area. Weights are particularly important when solving a graph. There are two solver types presented in the tutorial below:

  • shortest_path -- Find the shortest path between two points on a graph
  • multiple_routing -- Find the quickest route between a source point and many destination points; also known as travelling salesman

Because there are no explicit nodes in the tutorial graph, source and destination point(s) must be selected from any of the edges comprising the Washington, D.C., road network. Otherwise, the graph will not be able to traverse to the point and will result in a null solution.

Tutorial via REST Client

This tutorial can be run via the GAdmin API Tool to create and solve the graph, but any REST client will work. To access the API tool in GAdmin:

  1. Navigate to GAdmin and login (http://<kinetica-host>:8080/)
  2. In the top menu, click Query ‣ API
  3. Under Request Mode, select JSON

Create Graph

One graph is used for both solve graph examples later in the tutorial: dc_shape_graph, a graph based on the aforementioned dc_shape dataset. The dc_shape_graph graph is created with the following characteristics:

  • It is directed because the roads in the graph have directionality (one-way and two-way roads)
  • It has no explicitly defined nodes because the example relies on implicit nodes attached to the defined edges
  • The edges are derived from WKT LINESTRINGs in the shape column of the dc_shape table (EDGE_WKTLINE). Each road segment's directionality is derived from the direction column of the dc_shape table (EDGE_DIRECTION).
  • The weights are represented as distance, which is calculated as the length of the entire shape column's LINESTRING (in meters) divided by the number of points in the LINESTRING minus 1 (WEIGHTS_VALUESPECIFIED). The weights are matched to the edges using the same shape column as edges (WEIGHTS_EDGE_WKTLINE) and the same direction column as the edge direction (WEIGHTS_EDGE_DIRECTION).
  • It has no inherent restrictions for any of the nodes or edges in the graph
  • It utilizes the following options:
    • It will be replaced with this instance of the graph if a graph of the same name exists (recreate)
    • If nodes are within 0.00001 degrees (1 meter) of each other, they will be merged together (merge_tolerance)
    • The resulting graph's information will be placed into a table (graph_table) and an EDGE_WKTLINE column will be included so the graph can be visualized (enable_graph_draw)

To create the graph:

  1. In the API Tool, select /create/graph from the Endpoint drop-down menu

  2. Copy the following JSON into the Request Mode text box:

    {
      "graph_name": "dc_shape_graph",
      "directed_graph": true,
      "nodes": [],
      "edges": [
        "dc_shape.shape AS EDGE_WKTLINE",
        "dc_shape.direction AS EDGE_DIRECTION"
      ],
      "weights": [
        "dc_shape.shape AS WEIGHTS_EDGE_WKTLINE",
        "dc_shape.direction AS WEIGHTS_EDGE_DIRECTION",
        "ST_Length(dc_shape.shape,1)/(ST_NPOINTS(dc_shape.shape)-1) AS WEIGHTS_VALUESPECIFIED"
      ],
      "restrictions": [],
      "options": {
        "merge_tolerance": "0.00001",
        "recreate": "true",
        "enable_graph_draw": "true",
        "graph_table": "dc_shape_graph_table"
      }
    }
    
  3. Click Send Request

The response field on the right-hand side of the page will be populated with the server response:

------------------------------------------------------------
Thu Jan 16 2020 10:52:34 GMT-0500 (Eastern Standard Time)
------------------------------------------------------------
Endpoint: /create/graph
Time: 24549
Request: {
    "graph_name": "dc_shape_graph",
    "directed_graph": true,
    "nodes": [],
    "edges": [
        "dc_shape.shape AS EDGE_WKTLINE",
        "dc_shape.direction AS EDGE_DIRECTION"
    ],
    "weights": [
        "dc_shape.shape AS WEIGHTS_EDGE_WKTLINE",
        "dc_shape.direction AS WEIGHTS_EDGE_DIRECTION",
        "ST_Length(dc_shape.shape,1)/(ST_NPOINTS(dc_shape.shape)-1) AS WEIGHTS_VALUESPECIFIED"
    ],
    "restrictions": [],
    "options": {
        "merge_tolerance": "0.00001",
        "recreate": "true",
        "enable_graph_draw": "true",
        "graph_table": "dc_shape_graph_table"
    }
}
Response: {
    "num_nodes": 446491,
    "num_edges": 491461,
    "edges_ids": [],
    "info": {
        "status": "OK"
    }
}

Solve the Graph (Shortest Path)

The following scenario has been designed to illustrate a shortest path solution:

You work near the White House, and after you get off work, you'd like to attend a baseball game at the nearby ballpark. What's the shortest path you could take to get to the ballpark?

Important

The source and destination points were selected from endpoints of edges within the graph. The easiest way to review the points that make up an edge is using the WMS tool on the graph table (dc_roads_graph_table).

Source / Destination Source Destination
WKT POINT(-77.03511810000001 38.89876175) POINT(-77.00585175000001 38.87462997)
Location Description The corner of Madison Place Northwest and Pennsylvania Avenue Northwest The corner of N Street Southeast and Southeast 1st street
WMS Location ../../_images/dc_roads_sp_source.png ../../_images/dc_roads_sp_dest.png

To generate the solution:

  1. In the API Tool, select /solve/graph from the Endpoint drop-down menu

  2. Copy the following JSON into the Request Mode text box:

    {
      "graph_name": "dc_shape_graph",
      "weights_on_edges": [],
      "restrictions": [],
      "solver_type": "shortest_path",
      "source_nodes": ["POINT(-77.03511810000001 38.89876175)"],
      "destination_nodes": ["POINT(-77.00585175000001 38.87462997)"],
      "solution_table": "dc_shape_graph_solved_shortest_path",
      "options": {}
    }
    

    Note

    Because the tutorial graph was created using WKT linestrings, the /solve/graph call provides the source and destination points as WKT points.

  3. Click Send Request

The response field on the right-hand side of the page will be populated with the server response:

------------------------------------------------------------
Thu Jan 16 2020 11:40:33 GMT-0500 (Eastern Standard Time)
------------------------------------------------------------
Endpoint: /solve/graph
Time: 347
Request: {
    "graph_name": "dc_shape_graph",
    "weights_on_edges": [],
    "restrictions": [],
    "solver_type": "shortest_path",
    "source_nodes": [
        "POINT(-77.03511810000001 38.89876175)"
    ],
    "destination_nodes": [
        "POINT(-77.00585175000001 38.87462997)"
    ],
    "solution_table": "dc_shape_graph_solved_shortest_path",
    "options": {}
}
Response: {
    "result": true,
    "result_per_destination_node": [],
    "info": {
        "status": "OK"
    }
}

The solution output to WMS:

../../_images/dc_roads_graph_solved_shortest_path.png

Solve the Graph (Multiple Routing)

The following scenario has been designed to illustrate a multiple routing solution:

You're currently taking the subway to Union Station to visit Washington D.C. for the day. You would like to see some of the most iconic monuments and buildings in Washington, D.C. before returning back to Union Station. Starting from Union Station, what's the quickest route between each stop before returning back to Union Station?

Important

The source and destination points were selected from endpoints of edges within the graph. The easiest way to review the points that make up an edge is using the WMS tool on the graph table (dc_shape_graph_table).

Source / Destination Source Destination Destination Destination Destination
WKT POINT(-77.00576019 38.89677811) POINT(-77.03517151 38.8898201) POINT(-77.03626251 38.88068008) POINT(-77.04974365 38.89020157) POINT(-77.01207733 38.89072037)
Location Description Union Station Near the Washington Monument Near the Jefferson Memorial Near the Lincoln Memorial Near Capitol Hill
WMS Location ../../_images/dc_roads_mr_source.png ../../_images/dc_roads_mr_dest_wm.png ../../_images/dc_roads_mr_dest_jm.png ../../_images/dc_roads_mr_dest_lm.png ../../_images/dc_roads_mr_dest_ch.png

To generate the solution:

  1. In the API Tool, select /solve/graph from the Endpoint drop-down menu

  2. Copy the following JSON into the Request Mode text box:

    {
      "graph_name": "dc_shape_graph",
      "weights_on_edges": [],
      "restrictions": [],
      "solver_type": "multiple_routing",
      "source_nodes": ["POINT(-77.00576019 38.89677811)"],
      "destination_nodes": [
        "POINT(-77.03517151 38.8898201)",
        "POINT(-77.03626251 38.88068008)",
        "POINT(-77.04974365 38.89020157)",
        "POINT(-77.01207733 38.89072037)"
      ],
      "solution_table": "dc_shape_graph_solved_multiple_routing",
      "options": {}
    }
    

    Note

    Because the tutorial graph was created using WKT linestrings, the /solve/graph call provides the source and destination points as WKT points.

  3. Click Send Request

The response field on the right-hand side of the page will be populated with the server response:

------------------------------------------------------------
Thu Jan 16 2020 12:48:18 GMT-0500 (Eastern Standard Time)
------------------------------------------------------------
Endpoint: /solve/graph
Time: 963
Request: {
    "graph_name": "dc_roads_graph",
    "weights_on_edges": [],
    "restrictions": [],
    "solver_type": "multiple_routing",
    "source_nodes": [
        "POINT(-77.00576019 38.89677811)"
    ],
    "destination_nodes": [
        "POINT(-77.03517151 38.8898201)",
        "POINT(-77.03626251 38.88068008)",
        "POINT(-77.04974365 38.89020157)",
        "POINT(-77.01207733 38.89072037)"
    ],
    "solution_table": "dc_roads_graph_solved_multiple_routing",
    "options": {}
}
Response: {
    "result": true,
    "result_per_destination_node": [],
    "info": {
        "status": "OK"
    }
}

The solution output to WMS:

../../_images/dc_roads_graph_solved_multiple_routing.png

Tutorial via Terminal

Included below is the complete tutorial containing all the above requests and the necessary JSON files:

To run the complete sample, ensure the graphs_rest.sh and the JSON files are in the same directory; then switch to that directory and do the following:

./graphs_rest.sh <kinetica-host>