Convert XYZ-Tiles to BoundingBox (EPSG:3857-BBOX: minx,miny,maxx,maxy) to receive Tilesets 256x256 px - similar to WhooTS: http://whoots.mapwarper.net

Required: WMS-Server needs to support EPSG:3857

Calculation taken from: https://github.com/Tetramatrix/monstercurves/blob/master/GlobalMapTiles.php
No images will be served from this server. The script just calculate the BBOX and redirect to the WMS-Request GetMap

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Example usage:
You have a WMS to receive tiles in 256x256 size from for e.g. OsmAnd+ App

1. Get familiar with the GetCapabilites of the WMS
https://services.bgr.de/arcgis/services/geologie/guek200/MapServer/WMSServer?request=GetCapabilities&service=WMS

URL-MASK for OsmAnd+:
https://xyz2bbox.kreidefossilien.de/?wms=https://services.bgr.de/arcgis/services/geologie/guek200/MapServer/WMSServer&z={0}&x={1}&y={2}&l=1,2,4&&f=image/png8&t=true&v=1.3.0&m=

Parameter	Description	type		remarks/example

&wms		url to the WMS	url		https://services.bgr.de/arcgis/services/geologie/guek200/MapServer/WMSServer
&z		zoomlevel 	integer		{0} or {$z} -> 1 to 19
&x		x-Tile		integer		{1} or {$x} -> e.g. 1103
&y		y-Tile		integer		{2} or {$y} -> e.g. 687
&l		layername(s) 	string		see WMS-GetCapabilites, usually comma-separated list -> layer or 1,2,4 or layer1,layer2
&f		format received	string		see WMS-GetCapabilites	image/png8 or image/jpeg or image/png
&t		transparency 	boolean		see WMS-GetCapabilites	true/false (only usefull in combination with png or tiff)
&v		WMS-Version	string		see WMS-GetCapabilites	1.3.0 or 1.1.1 or 1.0.0
&m		map		string		see WMS-GetCapabilites	not needed for this example

Result:
The following Tile-URL
https://xyz2bbox.kreidefossilien.de/?wms=https://services.bgr.de/arcgis/services/geologie/guek200/MapServer/WMSServer&z=11&x=1103&y=687&l=1,2,4&&f=image/png8&t=true&v=1.3.0&m=

will redirect to this WMS-Response (Http-Header is set to "301, permanent moved")
https://services.bgr.de/arcgis/services/geologie/guek200/MapServer/WMSServer?BBOX=1545862.4600394,6574807.4249777,1565430.3392804,6594375.3042187&format=image/png8&version=1.3.0&layers=1,2,4&map=&transparent=true&service=WMS&request=GetMap&crs=EPSG:3857&srs=EPSG:3857&width=256&height=256&styles=

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"debuging" with parameter &d=true (optional, default is false)

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More Examples for OsmAnd+
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GK25 of Bavaria 
Legend: https://www.lfu.bayern.de/gdi/legende/geologie/dgk25/geoleinheit_dgk25.png

Create a folder e.g. "GK25 Bayern" and put a file named ".metainfo" with the following content in:
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[url_template]
https://xyz2bbox.kreidefossilien.de/?wms=https://www.lfu.bayern.de/gdi/wms/geologie/dgk25&z={0}&x={1}&y={2}&l=verfuegbarkeit_dgk25,geoleinheit_dgk25,strukturln_dgk25&f=image/png8&v=1.3.0&t=true
[ext]
.png
[min_zoom]
12
[max_zoom]
16
[tile_size]
256
[img_density]
32
[avg_img_size]
20000
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then copy the folder + .metainfo into ".../files/tiles/"-folder of the OsmAnd-App
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tbc