Calculating correct map extent/image

[jga at scot.cnes.fr]

On  8 Mar, Burkhard Sell wrote:
> hello,
>   we are using a java applet to communicate with the mapserver.
>   
>   for example if we zoom, we send the new map extent to the map server,
> and
>   get a image back.
> 
>   but problem is, that the extent of the image is not the same as the
> requested
>   extent, because the server fits it to the screen ratio.
>   what must we do to calculate/set the correct extent of the returned
> image?
> 		
>   is there any way to get the data calculated by the server back to the
> client?
> 
> we hope anybody can help :-))
> 
> Burkhard Sell

Hi,

I wrote this method to calculate the correct extent. It's derived from
the mapserver source code (i didn't remember which .c file :)

    /**
     *
     *  This method calculate the correct extent from a box extent.
     *  Assume x1Extent, y1Extent, x2Extent, y2Extent the requested extent
     *  x1Coord, y1Coord, x2Coord, y2Coord are the corrected coordinate
     *
     */
    public void setAdjustedCoordinates() {
	
	float cellsize, ox, oy;

	cellsize = (float) (Math.max((x2Extent - x1Extent) / (screenSize.width - 1), (y2Extent - y1Extent) / (screenSize.height - 1)));
	
	if(cellsize <= 0) {
	    System.out.println(" Error : Invalid coordinates adjustment!");
	    System.exit(0);
	}
	
	ox = ms_NINT( (float) (Math.max(((screenSize.width - 1) - (x2Extent - x1Extent) / cellsize) / 2, 0.0)));
	oy = ms_NINT( (float) (Math.max(((screenSize.height - 1) - (y2Extent - y1Extent) / cellsize) / 2, 0.0)));

	x1Coord = x1Extent - ox * cellsize;
	y1Coord = y1Extent - oy * cellsize;
	x2Coord = x2Extent + ox * cellsize;
        y2Coord = y2Extent + oy * cellsize;
    }

    
    /**
     *
     * See MS_MINT definition in map.h (cf:mapserver source code)
     * 
     */
    private float ms_NINT(float x) {
	if (x >= 0)
	    return (float) (x + 0.5);
	else
	    return (float) (x - 0.5);
    }


Regards

J

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