PostGIS GeoServer – Styling Layers with Multiple Geometries

draw ordergeometrygeoserverpostgiswms

I've build a table with multiple geometries in PostGIS. This table is published in GeoServer. Now I'm wondering how GeoServer handles this type of layer. specifically the drawing part.

My layer contains all three geometries, points, lines and polygons. In the ideal situation polygons are drawn first, lines second and point third. To prevent polygons overlapping the other geometry types.

The generated WMS looks rather good, all point and lines are visible. My question is: 'Does Geoserver draw objects according to its geometry, in a specific order?'

Best Answer

GeoServer draws things as defined by their rule order and then in feature order with each symbolizer (roughly the order they are in the table in your case).

The tricky thing is that when dealing with mixed geometries SLD will do funny things (and CSS and YSLD are just SLD in the end). Basically if you have the symbolizer you have specified will be applied to all of the geometries and they will be coerced in to the expected geometry type. So, for example, a point symbolizer will use the centroid of a line or polygon, while a polygon symbolizer will connect the ends of a linestring to make a polygon.

The best (and easiest plan) is to separate features out by geometry type into different tables. The next easiest plan is to use a geometryType filter to determine which symbolizer to apply.

While your map may currently look good what happens if the next feature you add is a large polygon the covers everything else.

Related Solutions

WFS Layer – How to Initialize in OpenLayers

Take a look at this code example:

var adresspt_wfs = new OpenLayers.Layer.Vector("Address points WFS", {
 strategies: [new OpenLayers.Strategy.BBOX(), saveStrategy],
    protocol: new OpenLayers.Protocol.WFS({
    url: "http://localhost:8080/geoserver/wfs",
    featurePrefix: "XXXX" //<-- GeoServer workspace name
    featureType: "RAILWAY",//<-- layer name
    featureNS: "http://localhost:8080/MIA", //<-- Edit Workspace Namespace URI
    srsName: "EPSG:900913",
    geometryName: "SDO_GEOMETRY" //<-- geometry field
  })
});

The featureNS property is equivalent to your Namespace URI in the Edit Workspace page of GeoServer:

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Here's a tutorial

[GIS] display multiple vector layers from single PostGis table in GeoServer using OpenLayers — REWORDED

Yes it's possible.

Starting with GeoServer 2.1.0 the user can also create a new layer by specifying a raw SQL query

You can create SQL Views which reference the same table using SQL Statements.

Instructions and Documentation

Update Per OpenLayers question in comment:

It really depends on how you want to serve out your data which depends on what kind and how much data you have.

If the data is vector data and not more than +-300 features you can use WFS. Add that layer like so: OpenLayers GeoServer WFS Layer Example

If the data is Raster data or you just want your layer served out as an image rather than vector features, then add that layer using WMS. Like so: OpenLayers WMS Layer Example

Update #2:

Based on your latest comment, what you can do is: add multiple wfs layers to your open layers map which point to ONE layer on your GeoServer but have a filter defined so you only get ONE feature back based on ID or some other attribute in your filter.

Take a look at this example.

Basically it will be something like:

var wfs = new OpenLayers.Layer.Vector("WFS", {
    strategies: [new OpenLayers.Strategy.BBOX()],
    protocol: new OpenLayers.Protocol.WFS({
        url: "http://demo.opengeo.org/geoserver/wfs",
        featureType: "tasmania_roads",
        featureNS: "http://www.openplans.org/topp"
    }),
    filter: new OpenLayers.Filter.Logical({
        type: OpenLayers.Filter.Logical.And,
        filters: [
            new OpenLayers.Filter.Comparison({
                type: OpenLayers.Filter.Comparison.EQUAL_TO,
                property: "id",
                value: "POLYGONID"
            })
        ]
    })
});