Does JOSM downscale aerial imagery?

[francois.lacombe]

Dear maintainers,

I'm currently experiencing trouble to get a new aerial layer at its highest scale in JOSM.
French government regularly releases 5cm scale imagery now and it's available through a WMTS server.

​https://wxs.ign.fr/ortho/geoportail/wmts?SERVICE=WMTS&VERSION=1.0.0&REQUEST=GetCapabilities
and select PCRS LAMB93 layer in it.

It appears that imagery isn't rendered at its full scale in JOSM, instead of QGis for instance.
I provide a joint screen capture to show differences between both.
Situation took at 6.4142065, 45.2456682

#19482 looks to be related but it doesn't come from imagery provider this time.

Is there parameters I mistaken or something regarding the poor imagery quality?

Best regards

[francois.lacombe]

Same imagery render differently in QGis or JOSM

[taylor.smock]

JOSM (by default) limits the max zoom to z20. It looks like this external source has a max zoom of z21 (look for <TileMatrix>21</TileMatrix> in the XML for PCRS LAMB93).

Assuming there are the appropriate permissions for OSM use, I would recommend adding it to wiki:Maps/France for others to use with the appropriate settings (like the max zoom set to 21). Otherwise, you can manually edit the max zoom in imagery preferences. It would look like wmts[21]:https://[rest of url].

[francois.lacombe]

Hi Taylor, thank you for this hint I wasn't aware of!

No problem to update Maps/France for that but I'm puzzeled by the wmts parameters.
In this URL: ​https://wxs.ign.fr/ortho/geoportail/wmts?SERVICE=WMTS&REQUEST=GetTile&VERSION=1.0.0&LAYER=PCRS.LAMB93&STYLE=normal&FORMAT=image/jpeg&tileMatrixSet=LAMB93_5cm_EPSG&tileMatrix=20&tileRow=107128&tileCol=18134

What should I add in the tileMatrix, tileRow and tileCol parameters please?

[taylor.smock]

Sorry it took me awhile to get back to you.

Why do you want to replace the parameters?

Use the default-layers attribute.

So it would look something like this:

    <entry>
        <name>Some name</name>
        <id>insert-stable-id-here</id>
        <category>map</category>
        <type>wmts</type>
        <url><![CDATA[https://wxs.ign.fr/ortho/geoportail/wmts?SERVICE=WMTS&REQUEST=GetCapabilities&VERSION=1.0.0]]></url>
        <permission-ref>insert permission ref here</permission-ref>
        <projections>
            <code>EPSG:2154</code>
        </projections>
        <default-layers>
            <layer name="PCRS.LAMB93" style="default" tile-matrix-set="LAMB93_5cm_EPSG" />
        </default-layers>
        <country-code>FR</country-code>
        <attribution-text>insert attribution text here</attribution-text>
        <attribution-url>insert attribution url here</attribution-url>
        <icon>insert icon link here</icon>
        <min-zoom>6</min-zoom>
        <max-zoom>21</max-zoom>
        <bounds min-lat='42.6976' min-lon='-3.80779' max-lat='48.8107' max-lon='6.92319'>
            <shape>
                <!-- FIXME (also fix the bounds). Use https://wiki.openstreetmap.org/wiki/JOSM/Plugins/Imagery-XML-Bounds to make it. -->
            </shape>
        </bounds>
    </entry>