WMTS does not support different tile sizes for layers using the same projection

[StefanB]

In imagery for Slovenia we have a reference to WMTS service:
https://josm.openstreetmap.de/wiki/Maps/Slovenia#GURS:DTK5wmts
Which fetches capabilities from
​http://prostor4.gov.si/ows2-gwc-pub/service/wmts?request=getCapabilities

Some of the layers there are in an older national projection EPSG:3912 (​https://epsg.io/3912 = D48/GK), and those layers are not positioned correctly in JOSM (eg in lower zoom it is shifter 100km to the north). This old projection is being phased out, but some legacy data is still in it.

The layers in newer projection EPSG:3794 (​https://epsg.io/3794 = D96/TM) are positioned much better

Whenever needed and possible, we use ​http://geocoordinateconverter.tk/ to convert data from the old projection to ETRS89 accurately, but int this case the layers are served via wmts service, giving us no influence.

Either

• EPSG:3912 projection should be better supported (probably not easy) to position the layer better or
• disable such layer selection in the "Select WMTS layer" dialog window
• add some additional warning that layer might not work at all

Current "Select WMTS layer" dialog:

[Klumbumbus]

and those layers are not positioned correctly in JOSM (eg in lower zoom it is shifter 100km to the north)

• At which zoom?
• At which position?
• What did you set as projection in JOSM?
• JOSM automatically reprojects, but using the "native" projection of the tiles might be better. At a quick test with JOSM reprojecting DTK5 EPSG:3912 to mercator I couldn't find misplaced tiles.

[Don-vip]

I tried too and it seems to work fine (offset between Bing and DTK5 EPSG:3912 less than 5m).

[StefanB]

Misplaced rendering

[StefanB]

Indeed, most of the problems encountered were with the layers starting with "table_gurs_pub...", eg the table_gurs_pub:SI.GURS.RPE.NA (Naselja, settlements) layer loads image:
​http://prostor4.gov.si/ows2-gwc-pub/service/wmts?SERVICE=WMTS&REQUEST=GetTile&VERSION=1.0.0&LAYER=table_gurs_pub:SI.GURS.RPE.NA&STYLE=&FORMAT=image/png&tileMatrixSet=EPSG:3912_ALL_SCALES_512pxl&tileMatrix=EPSG:3912_ALL_SCALES_512pxl:5&tileRow=4&tileCol=4
which is 512x512 px (got hint from the matrix set name, but confirmed in the actual image), which might screw up the positioning, which then renders badly:

(cyan is the "GURS: Road lines" layer, which matches very well to OSM data; violet is the table_gurs_pub:SI.GURS.RPE.NA layer)

[stoecker]

Hmm, maybe for WMTS we need to auto-detect the size, as we can't provide it in the XML...

[Don-vip]

Replying to stoecker:

Hmm, maybe for WMTS we need to auto-detect the size, as we can't provide it in the XML...

It's provided in the capabilities:

            <TileMatrix>
                <ows:Identifier>EPSG:3912_ALL_SCALES_512pxl:0</ows:Identifier>
                <ScaleDenominator>1250000.0</ScaleDenominator>
                <TopLeftCorner>370210.0 200055.0</TopLeftCorner>
                <TileWidth>512</TileWidth>
                <TileHeight>512</TileHeight>
                <MatrixWidth>2</MatrixWidth>
                <MatrixHeight>1</MatrixHeight>
            </TileMatrix>

[Don-vip]

Bug is in WMTSTileSource:

        if (tileProjection != null) {
            // no support for non-square tiles (tileHeight != tileWidth)
            // and for different tile sizes at different zoom levels
            Collection<Layer> projLayers = getLayers(null, tileProjection.toCode());
            if (!projLayers.isEmpty()) {
                cachedTileSize = projLayers.iterator().next().tileMatrixSet.tileMatrix.get(0).tileHeight;
                return cachedTileSize;
            }
        }

We rely only on projection, and use the tile dimensions of the first layer matching the current projection, instead of using the actual size defined for the current tile matrix.

[Don-vip]

In 13539/josm:

fix #16084 - WMTS: support different tile sizes for layers using the same projection

[StefanB]

Wonderful!
I will try it as soon as the josm-latest.jar with this fix (version 13539 or higher) is available.
Thank you!!!

[Don-vip]

In 13542/josm:

see #16084 - remove unused code

[StefanB]

Tested version 13544, and layers seem to be rendered perfectly!