Label coordinate position of Grid lines

Question

I read How can I label the coordinate position of the grid coordinate lines but I still do not understand how to use the LineFeatureBuilder class to label the grid lines. Could someone let me know how do I use this class in my code to get the labels? Code creating the lines:

        List<OrthoLineDef> lineDefs =
                Arrays.asList(
                        new OrthoLineDef(LineOrientation.VERTICAL, 2, 10.0),
                        new OrthoLineDef(LineOrientation.HORIZONTAL, 2, 10.0)
                );
        double vertexSpacing = 0.1;
        SimpleFeatureSource grid = Lines.createOrthoLines(gridBounds, lineDefs, vertexSpacing);
....
        Style latlonStyle = SLD.createLineStyle( strokeColor, strokeWidth );

Answer 1

I wrote a blog post about this a while back, 1st you need to override org.geotools.grid.GridFeatureBuilder to add the X or Y values to the lines (so you can draw them later):

package com.ianturton.cookbook.utilities.gridsupport;

import java.text.Format;
import java.util.Map;

import org.geotools.grid.GridElement;
import org.geotools.grid.GridFeatureBuilder;
import org.geotools.grid.ortholine.LineOrientation;
import org.geotools.grid.ortholine.OrthoLine;
import org.geotools.measure.CoordinateFormat;
import org.locationtech.jts.geom.Coordinate;
import org.opengis.feature.simple.SimpleFeatureType;
import org.opengis.referencing.cs.CoordinateSystem;

public class LineFeatureBuilder extends GridFeatureBuilder {
  /** Default feature TYPE name: "linegrid" */
  public static final String DEFAULT_TYPE_NAME = "linegrid";

  /** Name used for the integer id attribute: "id" */
  public static final String ID_ATTRIBUTE_NAME = "id";

  /**
   * Name of the Integer level attribute ("level")
   */
  public static final String LEVEL_ATTRIBUTE_NAME = "level";

  /**
   * Name of the Object value attribute ("value")
   */
  public static final String VALUE_ATTRIBUTE_NAME = "value";

  public static final String VALUE_LABEL_NAME = "label";

  protected int id;
  private SimpleFeatureType type;
  private CoordinateFormat formatter;
  private Format xFormat;
  private Format yFormat;
  private String xUnit;
  private String yUnit;

  public LineFeatureBuilder(SimpleFeatureType type2) {
    super(type2);
    this.type = type2;
    formatter = new CoordinateFormat();
    formatter.setNumberPattern("##0.00");
    formatter.setAnglePattern("DD.dd");

    formatter.setCoordinateReferenceSystem(type.getCoordinateReferenceSystem());
    xFormat = formatter.getFormat(0);
    yFormat = formatter.getFormat(1);
    CoordinateSystem coordinateSystem = type.getCoordinateReferenceSystem().getCoordinateSystem();
    xUnit = "" + coordinateSystem.getAxis(0).getUnit().toString();
    yUnit = "" + coordinateSystem.getAxis(1).getUnit().toString();
  }

  @Override
  public void setAttributes(GridElement el, Map<String, Object> attributes) {
    if (el instanceof OrthoLine) {
      OrthoLine orthoLine = (OrthoLine) el;
      attributes.put(ID_ATTRIBUTE_NAME, ++id);
      attributes.put(LEVEL_ATTRIBUTE_NAME, orthoLine.getLevel());

      Coordinate v0 = orthoLine.getVertices()[0];
      Double value = null;
      String label = "";
      if (orthoLine.getOrientation() == LineOrientation.HORIZONTAL) {
        value = v0.y;
        label = yFormat.format(v0.y) + yUnit;
      } else {
        value = v0.x;
        label = xFormat.format(v0.x) + xUnit;
      }
      attributes.put(VALUE_ATTRIBUTE_NAME, value);
      attributes.put(VALUE_LABEL_NAME, label);

    } else {
      throw new IllegalArgumentException("Expected an instance of OrthoLine");
    }
  }

}

Then you can create the "grid" using something like:

ReferencedEnvelope bounds = ReferencedEnvelope.create(new Envelope(xMin, xMax, yMin, yMax),
    coordinateReferenceSystem);

SimpleFeatureType type = (SimpleFeatureType) GridUtilities.buildType(coordinateReferenceSystem);
List<OrthoLineDef> lineDefs = Arrays.asList(
    // vertical (longitude) lines
    new OrthoLineDef(LineOrientation.VERTICAL, 2, xStep),
    // horizontal (latitude) lines
    new OrthoLineDef(LineOrientation.HORIZONTAL, 2, yStep));

// Specify vertex spacing to get "densified" polygons
double vertexSpacing = 0.1;
grid = Lines.createOrthoLines(bounds, lineDefs, vertexSpacing, new LineFeatureBuilder(type));

The final trick is to make the style draw the labels as well as the lines:

  Style red = SLD.createLineStyle(Color.red, 1.0f);
  ((LineSymbolizer)red.featureTypeStyles().get(0).rules()
    .get(0).symbolizers().get(0)).getStroke().setOpacity(ff.literal(0.5));
  layer = new FeatureLayer(featureSource, style);
  layer.getBounds().getCoordinateReferenceSystem();
  ReferencedEnvelope gridBounds = layer.getBounds();

  StyleBuilder sb = new StyleBuilder();
  java.awt.Font font = java.awt.Font.decode("Arial");
  TextSymbolizer text = sb.createTextSymbolizer(Color.red,
  sb.createFont(font), "label");

  LabelPlacement lp = sb.createLinePlacement(ff.literal(4));
  text.setLabelPlacement(lp);
  red.featureTypeStyles().get(0).rules().get(0).symbolizers().add(text);
  Layer gridLayer = new FeatureLayer(grid, red);

Then add gridLayer to your map with all your other layers.

Update

Gridutilities.buildType:

  private static FeatureType buildType(CoordinateReferenceSystem crs) {
    SimpleFeatureTypeBuilder tb = new SimpleFeatureTypeBuilder();
    tb.setName("grid");
    tb.add(LineFeatureBuilder.DEFAULT_GEOMETRY_ATTRIBUTE_NAME, LineString.class, crs);
    tb.add(LineFeatureBuilder.ID_ATTRIBUTE_NAME, Integer.class);
    tb.add(LineFeatureBuilder.LEVEL_ATTRIBUTE_NAME, Integer.class);
    tb.add(LineFeatureBuilder.VALUE_LABEL_NAME, String.class);
    tb.add(LineFeatureBuilder.VALUE_ATTRIBUTE_NAME, Double.class);
    return tb.buildFeatureType();
  }