Hello again!   I'm using a US Map via Unfolding, and overlaying a PImage onto it that represents a weather radar image.

Radar Image:
http://mesonet.agron.iastate.edu/archive/data/2013/05/31/GIS/ridge/ICT/N0Q/ICT_N0Q_201305312339.png

The "World File" that defines it's bounds is here:
http://mesonet.agron.iastate.edu/archive/data/2013/05/31/GIS/ridge/ICT/N0Q/ICT_N0Q_201305312339.wld

0.010483 (X pixel size in lon units per pixel)
0.0 (rotation)
0.0 (rotation)
-0.010483 (Y pixel size in lat units per pixel)
-102.684387 (Longitude upper left corner)
42.895387 (Latitude upper left corner)

The center location of the PImage is correct in my code, which is over Wichita, Kansas (37.6922,-97.3372).  but I don't know how to scale it for the correct size in relation to the US Map.  The radar image appears to be about 10 degrees tall and wide, which roughly fits with pixel size * image size (1000x1000 px).

Here is the code I'm using.  I need some help in translating the World File into a value I can use for 's' for scaling, or another method of doing so.  I know the center coordinates and the upper left coordinates.

Code snippets of what I have:
PGraphics pg;
PImage img = loadImage("http://mesonet.agron.iastate.edu/archive/data/2013/05/31/GIS/ridge/ICT/N0Q/ICT_N0Q_201305312339.png")';

pg.pushMatrix();
pg.translate(x,y); // x and y represent the center of the image in pixels (400x400px in my case)
pg.scale(s);
pg.image(img, -(img.width/2), -(img.height/2)); // Set to center of image.  Image is 1000x1000 px
pg.popMatrix();

Thanks!

 I just got started using Unfolding and am excited at the possibilities.  My first project is to map a GPS log over a map, with an arrow PNG image file that rotates based on the GPS direction.

 Without rotation, the icon displays correctly on the map.  With rotation however, the pivot point of rotation appears to be the in upper left corner of the screen.  I know from lots of Googling that you can use transform() and an image location of (0,0) to hack around this.

 However, I've found that when dealing with an Unfolding Map that translate() has no effect on the pivot point.  It merely shifts the pivot point that many pixels, with the icon still way out from the center of rotation.  The icon's distance from the pivot point seems to be about half the map's height and width.

 Obviously I'm doing something wrong here.  Here's my stripped down code below, using the ImageMarker class I found online.  I would like for it rotate the icon in place on the map center.  If I comment out the rotate(), it shows up at the map center.  

Thanks for any insight!

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import processing.core.PApplet;
import processing.core.PGraphics;
import processing.core.PImage;
import codeanticode.glgraphics.GLConstants;
import de.fhpotsdam.unfolding.UnfoldingMap;
import de.fhpotsdam.unfolding.geo.Location;
import de.fhpotsdam.unfolding.marker.AbstractMarker;
import de.fhpotsdam.unfolding.providers.OpenStreetMap;

public class GPSMap extends PApplet {
    //public class HelloUnfoldingWorld extends PShape {

    UnfoldingMap map;
    String CAR_ICON_FILE = "http://www.blueskybust.com/gpsicon-north.png";
    int MAP_WIDTH_HEIGHT = 800;
   
    float TEST_LAT = 44.95f;
    float TEST_LON = -93.55f;
   
    public void setup() {
        size(MAP_WIDTH_HEIGHT, MAP_WIDTH_HEIGHT, GLConstants.GLGRAPHICS);
        background(0);
       
        map = new UnfoldingMap(this, new OpenStreetMap.OpenStreetMapProvider());
        map.zoomAndPanTo(new Location(TEST_LAT, TEST_LON), 5);
        PImage carimage = loadImage(CAR_ICON_FILE);
        ImageMarker carMarker = new ImageMarker(new Location(TEST_LAT, TEST_LON),  carimage); // Just to initialize
        map.addMarkers(carMarker);

    }

    public void draw() {
        background(0);
        map.draw();
    }

    public class ImageMarker extends AbstractMarker {

        PImage img;
        int testheading = 0;

        public ImageMarker(Location location, PImage img) {
        super(location);
        this.img = img;
        }

        @Override
        public void draw(PGraphics pg, float x, float y) {
        testheading = testheading + 1;
           
        pg.pushMatrix();
        pg.rotateZ((float)Math.toRadians(testheading));
        //pg.rotate((float)Math.toRadians(testheading)); // Same result as rotateZ
        pg.image(img, x, y);
        pg.popMatrix();

        }


        @Override
        protected boolean isInside(float checkX, float checkY, float x, float y) {
        return checkX > x && checkX < x + img.width && checkY > y && checkY < y + img.height;
        }
    }
}