How to correctly render features with GeoTools to an image using AffineTransformation?

Question

I'm trying to correctly render some features I read from a featuretable of a PostGIS enabled database with GeoTools to an image.

My configuration:

• PostgreSQL 8.4
• PostGIS 1.5
• Osmosis 0.40.1
• OSMembrane build 845
• GeoTools 2.7.4

Rendering some features inside a bounding box works fine so far.
The issue: I get a result that is

1. rotated 90° (clockwise)
2. mirrored on the y-axis

The features I want to render are based on this CoordinateReferenceSystem

GEOGCS["WGS 84", 
  DATUM["World Geodetic System 1984", 
    SPHEROID["WGS 84", 6378137.0, 298.257223563, AUTHORITY["EPSG","7030"]], 
    AUTHORITY["EPSG","6326"]], 
  PRIMEM["Greenwich", 0.0, AUTHORITY["EPSG","8901"]], 
  UNIT["degree", 0.017453292519943295], 
  AXIS["Geodetic latitude", NORTH], 
  AXIS["Geodetic longitude", EAST], 
  AUTHORITY["EPSG","4326"]]

I'm aware of excuting an affine transformation, so I have written the following piece of code:

public void render(final MapContext mapContext, final Graphics2D graphics) throws IOException 
{
    Rectangle renderingArea = new Rectangle(this.mapWidth, this.mapHeight);

    GTRenderer renderer = new StreamingRenderer();
    renderer.setContext(mapContext);

    //move the result to a visisble area
    AffineTransform translate = AffineTransform.getTranslateInstance(mapHeight, mapWidth);
    //rotate 180° anti-clockwise
    AffineTransform rotate = AffineTransform.getRotateInstance(Math.PI);
    //exchange x and y 
    AffineTransform mirror = new AffineTransform(0, 1, 1, 0, 0, 0);

    AffineTransform transform = new AffineTransform(translate);
    transform.concatenate(rotate);
    transform.concatenate(mirror);

    graphics.transform(transform);

    renderer.paint(graphics, renderingArea, mapContext.getAreaOfInterest());
}

This works and makes the features look fine! On the other hand, this does not feel quite right. The question is, why I can't use the same transformation I applied on the graphics-object as a method parameter of the renderer's paint-method?

e.g.

//move the result to a visisble area
AffineTransform translate = AffineTransform.getTranslateInstance(mapHeight, mapWidth);
//rotate 180° anti-clockwise
AffineTransform rotate = AffineTransform.getRotateInstance(Math.PI);
//exchange x and y 
AffineTransform mirror = new AffineTransform(0, 1, 1, 0, 0, 0);

AffineTransform transform = new AffineTransform(translate);
transform.concatenate(rotate);
transform.concatenate(mirror);

renderer.paint(graphics, renderingArea, mapContext.getAreaOfInterest(), transform);

This always leads to an empty screen. I think, it is rendered somewhere outside the visible area. I know about the tutorials at the geotools website, but I miss some place where everything is put together.

I'm looking forward to any helpful hints.

Answer 1

The most likely problem is Axis-Order, read this page http://docs.geotools.org/latest/userguide/library/referencing/order.html and see if that solves your problem. If that isn't the issue then you'll probably want to look at the referencing faq - I've never had to write my own affine transform to render features so I would expect the issue to be answered there or in one of the other tutorials.