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A map provider says on its webpage that the ground resolution (respectively pixelsize) is 0.2m x 0.2m.

The WMTS-Capabilities document states on the highest zoom level (ows:Identifier 16) a scale denominator of 267.When considering the standard pixel size of 0.28mm we have everything to calculate the map scale through:

pixelSpan = scaleDenominator × 0.28 10-3 / metersPerUnit(crs);
where:
metersPerUnit(Webmercator) => 1 
pixelSize => 0.07

The calculated ground resolution of 0.07m is slightly off the 0.2m.
The unit of Web Mercator is one meter which leads to one meter per unit, right? But where did I get wrong?

When loading the map in QGIS and zooming in to the maximum and then measured the pixel size I also arrived at 0.07 meters.

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  • Have you tried loading the WMTS into a GIS, zoomed completely in and then measured the resolution/pixelsize?
    – Erik
    Commented Aug 19, 2021 at 8:38
  • Ah no, good point. I ll try that with QGis
    – theDrifter
    Commented Aug 19, 2021 at 8:40
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    Just because the server will serve data with that resolution it doesn't mean that the data itself is that resolution, i.e. there can be many screen pixels to the image pixel.
    – Ian Turton
    Commented Aug 19, 2021 at 10:03
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    Calculating scale based on Web Mercator is an exercise in futility, since distances off the Equator can't be accurate (and approach infinitely inaccurate at the poles).
    – Vince
    Commented Aug 19, 2021 at 12:43
  • @Erik yes i tried and the result match the calculated value
    – theDrifter
    Commented Aug 19, 2021 at 13:55

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