[GIS] How to clean/fix polygons in a Node.js application

geojsonmongodbnode-jsturf

I am working on a simple Node.js application where users can walk around an area with a mobile device using GPS. This track is stored as a Polygon, but sometimes (due to inaccurate GPS signals or users not walking strictly around something) the Polygon is invalid GeoJSON.

I am looking for a way to integrate cleanup/fixing functionality for my user-generated Polygons in my Node.js application that uses a MongoDB (Turf being my main tool for working with GeoJSON).

I have briefly looked at ST_MakeValid and prepair which both seem to do what I need, but I don't see an easy way to integrate either into my stack.

The question is whether there are any libraries that are either written in JavaScript or can easily be wrapped to be used via an npm and play nicely with my existing stack and doesn't require bringing in heavy-weights like PostGIS.

Best Answer

Although I am not cleaning up Polygons I have found a better approach. As users gather data for the polygon I think it may be better to simply collect all points and then use turf.concave to draw a Polygon. Technically it is not 100% accurate but given the jumpy GPS signals the solution is good enough for me.

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[GIS] How to store lines and polygons in JSON documents

GeoJSON here are the SPECs.

Here's an example of a line and a polygon:

{ "type": "FeatureCollection",
  "features": [
    { "type": "Feature",
      "geometry": {"type": "Point", "coordinates": [102.0, 0.5]},
      "properties": {"prop0": "value0"}
      },
    { "type": "Feature",
      "geometry": {
        "type": "LineString",
        "coordinates": [
          [102.0, 0.0], [103.0, 1.0], [104.0, 0.0], [105.0, 1.0]
          ]
        },
      "properties": {
        "prop0": "value0",
        "prop1": 0.0
        }
      },
    { "type": "Feature",
       "geometry": {
         "type": "Polygon",
         "coordinates": [
           [ [100.0, 0.0], [101.0, 0.0], [101.0, 1.0],
             [100.0, 1.0], [100.0, 0.0] ]
           ]
       },
       "properties": {
         "prop0": "value0",
         "prop1": {"this": "that"}
         }
       }
     ]
   }

[GIS] How to perform spatial queries on polygons in mongodb

Currently MongoDB does not support these spatial operations - only Geospatial Indexing of 2d points is supported with some basic accompanying queries (near, within). If you need them you would need to develop support from scratch. Hopefully in the future this will be included.

However if you are interested in storing spatial data in a NoSQL database (instead of a standard relational database, such as PostGIS) you could try CouchDB with the geocouch extension. Geocouch uses GeoJSON to store geometry so polygons can be stored. However as far as I can see only boundnig box queries are supported so far - which you could use to narrow your search - with hopefully polygon and radius search, and srs support coming soon. (Also, a tutorial that I found from Todd Jackson gives a good run-through on getting started. And see this question on GIS SE.).

Best Answer

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[GIS] How to store lines and polygons in JSON documents

[GIS] How to perform spatial queries on polygons in mongodb

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