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POOpenstreetmap Viewer: coordinate-transformation error
 

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  1. POOpenstreetmap Viewer: coordinate-transformation error
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    <p>I'm struggling with a problem: I want to access openstreetmap via my Java application. I wrote a <code>JComponent</code> which is able to show tiles downloaded from openstreetmap. The problem is that in the formula which calculates the y-position (see FIXME in the sourcecode) of the downloaded picture it is an error and I'm not able to find it. Some parts of the code are copied from <a href="http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames" rel="nofollow">http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames</a>. The crazy thing is that the <code>x-position</code> is correct. The <code>goTo()</code> method is used to determine which place of the map should be in the center of the <code>JComponent</code>-View!</p> <pre><code>package ui; import java.awt.Graphics; import java.awt.Image; import javax.swing.JComponent; public class OSMViewer extends JComponent { private static final long serialVersionUID = 1L; protected ImageHandler imagehandler = null; protected int zoomlevel = 0; protected double center_deg_lon = 0.0; protected double center_deg_lat = 0.0; final double DEGY = 85.0511; final double DEGX = 180.0; public OSMViewer(ImageHandler imagehandler) { this.imagehandler = imagehandler; // TODO goTo(13, 30.0, 30.0); } public void goTo(final int zoom, final double lon, final double lat) { zoomlevel = zoom; center_deg_lon = lon; center_deg_lat = lat; repaint(); } // deg public int getTileNumberX(final int zoom, final double lon) { int xtile = (int) Math.floor((lon + 180) / 360 * (1 &lt;&lt; zoom)); return xtile; } // deg public int getTileNumberY(final int zoom, final double lat) { int ytile = (int) Math .floor((1 - Math.log(Math.tan(Math.toRadians(lat)) + 1 / Math.cos(Math.toRadians(lat))) / Math.PI) / 2 * (1 &lt;&lt; zoom)); return ytile; } // deg public double getLonDegPx(final int zoom) { double deg_px = 2 * DEGX / (Math.pow(2, zoom) * 256); return deg_px; } // deg public double getLatDegPx(final int zoom) { double deg_px = 2 * DEGY / (Math.pow(2, zoom) * 256); return deg_px; } // deg public int getPxX(final int zoom, final double lon) { return (int) (((lon + DEGX) / (2 * DEGX)) * Math.pow(2, zoom) * 256); } // deg public int getPxY(final int zoom, final double lat) { return (int) (((DEGY - lat) / (2.0 * DEGY)) * Math.pow(2.0, zoom) * 256.0); } public void paintComponent(Graphics g) { int x = getTileNumberX(zoomlevel, center_deg_lon); int y = getTileNumberY(zoomlevel, center_deg_lat); String str = ("" + zoomlevel + "/" + x + "/" + y); System.out.println(str); int xpos = (x * 256) - getPxX(zoomlevel, center_deg_lon) + (getWidth() / 2); // FIXME int ypos = (y * 256) - getPxY(zoomlevel, center_deg_lat) + (getHeight() / 2); Image image = imagehandler.getImage(str); if (image != null) { g.drawImage(image, xpos, ypos, this); } g.drawLine(0, getHeight() / 2, getWidth(), getHeight() / 2); g.drawLine(getWidth() / 2, 0, getWidth() / 2, getHeight()); } } </code></pre>
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    1. PTQuestion
    1. USJonathan Lam
    1. USuser2991452
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      1. POOpenstreetmap Viewer: coordinate-transformation error
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      1. VTUpMod
    1. COInside getPxX you are using int constants 2 and 256, and inside getPxY - double 2.0, 256.0. Try to use int inside getPxY.
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      1. POOpenstreetmap Viewer: coordinate-transformation error
      1. USAlexey Odintsov
    2. COi just tried but thx
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      1. POOpenstreetmap Viewer: coordinate-transformation error
      1. USuser2991452
    3. COYou may see [JMapViewer](http://wiki.openstreetmap.org/wiki/JMapViewer) [source code](http://svn.openstreetmap.org/applications/viewer/jmapviewer/src/org/openstreetmap/gui/jmapviewer/OsmMercator.java). Maybe it helps you.
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      1. POOpenstreetmap Viewer: coordinate-transformation error
      1. USAlexey Odintsov
 

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