How to draw a line on a shapefile using Geotools

Question

I have a shapefile that is opened and looks as such:

Java Geotools Demo

Now I am attempting to draw a line from two points I click on that map; however the code they give for the QuickStart.java example is exceptionally vague.

Here is their code:

package org.geotools.tutorial;

import java.io.File;

import org.geotools.data.FileDataStore;
import org.geotools.data.FileDataStoreFinder;
import org.geotools.data.simple.SimpleFeatureSource;
import org.geotools.map.FeatureLayer;
import org.geotools.map.Layer;
import org.geotools.map.MapContent;
import org.geotools.styling.SLD;
import org.geotools.styling.Style;
import org.geotools.swing.JMapFrame;
import org.geotools.swing.data.JFileDataStoreChooser;
import org.geotools.geometry.jts.JTSFactoryFinder;
import com.vividsolutions.jts.geom.Coordinate;
import com.vividsolutions.jts.geom.LineString;
/**
 * Prompts the user for a shapefile and displays the contents on the screen in a map frame.
 * <p>
 * This is the GeoTools Quickstart application used in documentationa and tutorials. *
 */
public class Quickstart {

    /**
     * GeoTools Quickstart demo application. Prompts the user for a shapefile and displays its
     * contents on the screen in a map frame
     */
    public static void main(String[] args) throws Exception {
        // display a data store file chooser dialog for shapefiles
        File file = JFileDataStoreChooser.showOpenFile("shp", null);
        if (file == null) {
            return;
        }

        FileDataStore store = FileDataStoreFinder.getDataStore(file);
        SimpleFeatureSource featureSource = store.getFeatureSource();

        // Create a map content and add our shapefile to it
        MapContent map = new MapContent();
        map.setTitle("Quickstart");

        Style style = SLD.createSimpleStyle(featureSource.getSchema());
        Layer layer = new FeatureLayer(featureSource, style);
        map.addLayer(layer);

        // Now display the map
        JMapFrame.showMap(map);
    }

}

Now, where I am confused is as to what method I should use to click two points and draw a line between them?

Anyone have any good resources on this? I've read up on the GeoTools documentation and am still a bit confused.

I attempted to do the generic code on the site but it does not appear on the map.

GeometryFactory geometryFactory = JTSFactoryFinder.getGeometryFactory( null );

   Coordinate[] coords  =
     new Coordinate[] {new Coordinate(0, 2), new Coordinate(2, 0), new Coordinate(8, 6) };

    LineString line = geometryFactory.createLineString(coords);
    Style style2 = SLD.createLineStyle(Color.BLUE, 1);
    Layer layer2 = new FeatureLayer(featureSource, style2);

For more information; I am just following along with the various Geotool tutorials; I attempted their "Style" tutorial and that left me without any luck as well. — Timothy Frisch, Jul 01 '14 at 20:24
Do you also have a code, where you append the line to layer, and show that layer? Your snippets don't contain those lines for my eyes. Generating a line object in memory does not mean anything would come to screen. — mico, Jul 07 '14 at 19:03
I had done a little bit of work with the geometric factory but I am not sure how layers work out in geotools. I had spent quite a few days working with it with no fruition. — Timothy Frisch, Jul 07 '14 at 19:16

Jur_ · Accepted Answer · 2014-07-08T13:46:05.150

Adding the line to a collection which you can add to the layer:

You should create a SimpleFeature from your LineString (this is such that the geometric line actually gets GeoReferenced). Make sure you add realistic coordinates though: The coordinates from the 2nd snipped would result in a relatively small line.
Create a new DefaultFeatureCollection (memory-stored collection) to which you can add the SimpleFeature. (Right now, in the 2nd snipped the line isn't added anywhere for drawing.)
```
DefaultFeatureCollection lineCollection = new DefaultFeatureCollection();
lineCollection.add(simpleFeature);
```
Add the DefaultFeatureCollection rather than the FeatureSource to the new created layer as a constructor parameter.
```
Layer layer = new FeatureLayer(lineCollection, style);
```
add the layer to the map like in your first snipped.
```
map.addLayer(layer);
```

For the creation of the SimpleFeature, see also the Feature Tutorial

The tutorial you pointed just show HOW to draw Features. You went further and show WHY we have to use each class. I've a little lost until now on creating features on map just copying/pasting snipets without really know why. Thanks. — Magno C, Mar 30 '23 at 16:17

How to draw a line on a shapefile using Geotools

1 Answers1