WMS ScaleHint precision

[Eijnden, B. van den (Bart)]

Hi list,

I am running into ScaleHint precision issues, at least it is my guess this
has to do with precision. It seems to me the values outputted to the WMS
Capabilities don't have enough precision.

My MAP file has 3 layers:

layer1: MINSCALE=250,000 MAXSCALE=5,000,000
layer2: MINSCALE=75,000 MAXSCALE=250,000
layer3: MINSCALE=0 MAXSCALE=75,000

The ScaleHint values are:

layer1: <ScaleHint min="124.726" max="2494.51" />
layer2: <ScaleHint min="37.4177" max="124.726" />
layer3: <ScaleHint min="0" max="37.4177" />

If I do MAXSCALE for layer1 on my calculator I get:
2494,5142421481852288355319843683

My application translates this back to scale values using (taken from
wmsparse.c which is part of Chameleon):

#define INCHES_PER_METER 39.3701

#ifndef M_SQRT2
# define M_SQRT2        1.41421356237309504880  /* sqrt(2) */
#endif

double scaleHintToScaleDenominator( double dScaleHint, double dResolution)
{
    if (dScaleHint <= 0)
        return -1.0;

    if (dResolution <= 0)
        dResolution = 72.0;

    return (dScaleHint * INCHES_PER_METER * dResolution / M_SQRT2);
}

The result is:
layer1: MINSCALE=250000,57705, MAXSCALE=4999991,49705
layer2: MINSCALE=74999,97268,MAXSCALE=250000,57705
layer3: MINSCALE=-1,MAXSCALE=74999,97268

As you can see, especially for layer 1 the results are (way) off.

Where is the problem situated? Can it be fixed by having more precision in
the WMS GetCapabilities for scalehint values?

Thanks in advance.

Best regards,
Bart


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