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QGIS Server 3.4 supports WMTS 1.0.0 OGC standard.

In QGIS project properties, the user can defined:

• which part of the project (all the project, layer groups or layers) has to be published through WMTS standard
• the min scale of the tiles

QGIS Server reused the CRS defined in the WMS capabilities configuration for WMTS.

To manage the tile cache, a QGIS Server plugin with a QgsServerCacheFilter class has to be installed and loaded by QGIS Server.

By default, QGIS Server only caches WMS GetCapabilities document in memory. With WMTS implementation, it is necessary to have a way to cache tiles. But the cache manager has not been developed to only cache tiles.

The cache manager plugin, can be used to cache:

• WMS, WFS, WCS, WMTS GetCapabilities documents
• WFS DescribeFeatureType documents
• WCS DescribeCoverage documents
• WMTS GetTile images
• WMS GetLegendGraphic images

Here is a python cache manager class, which do not verifying if the QGIS project has changed:

class PyServerCache(QgsServerCacheFilter):

    """ Used to have restriction access """

    # Be able to deactivate the access control to have a reference point
    _active = False

    def __init__(self, server_iface):
        super(QgsServerCacheFilter, self).__init__(server_iface)

        self._cache_dir = os.path.join(tempfile.gettempdir(), "qgs_server_cache")
        if not os.path.exists(self._cache_dir):
            os.mkdir(self._cache_dir)

        self._tile_cache_dir = os.path.join(self._cache_dir, 'tiles')
        if not os.path.exists(self._tile_cache_dir):
            os.mkdir(self._tile_cache_dir)

    def getCachedDocument(self, project, request, key):
        m = hashlib.md5()
        paramMap = request.parameters()
        urlParam = "&".join(["%s=%s" % (k, paramMap[k]) for k in paramMap.keys()])
        m.update(urlParam.encode('utf8'))

        if not os.path.exists(os.path.join(self._cache_dir, m.hexdigest() + ".xml")):
            return QByteArray()

        doc = QDomDocument(m.hexdigest() + ".xml")
        with open(os.path.join(self._cache_dir, m.hexdigest() + ".xml"), "r") as f:
            statusOK, errorStr, errorLine, errorColumn = doc.setContent(f.read(), True)
            if not statusOK:
                print("Could not read or find the contents document. Error at line %d, column %d:\n%s" % (errorLine, errorColumn, errorStr))
                return QByteArray()

        return doc.toByteArray()

    def setCachedDocument(self, doc, project, request, key):
        if not doc:
            print("Could not cache None document")
            return False
        m = hashlib.md5()
        paramMap = request.parameters()
        urlParam = "&".join(["%s=%s" % (k, paramMap[k]) for k in paramMap.keys()])
        m.update(urlParam.encode('utf8'))
        with open(os.path.join(self._cache_dir, m.hexdigest() + ".xml"), "w") as f:
            f.write(doc.toString())
        return os.path.exists(os.path.join(self._cache_dir, m.hexdigest() + ".xml"))

    def deleteCachedDocument(self, project, request, key):
        m = hashlib.md5()
        paramMap = request.parameters()
        urlParam = "&".join(["%s=%s" % (k, paramMap[k]) for k in paramMap.keys()])
        m.update(urlParam.encode('utf8'))
        if os.path.exists(os.path.join(self._cache_dir, m.hexdigest() + ".xml")):
            os.remove(os.path.join(self._cache_dir, m.hexdigest() + ".xml"))
        return not os.path.exists(os.path.join(self._cache_dir, m.hexdigest() + ".xml"))

    def deleteCachedDocuments(self, project):
        filelist = [f for f in os.listdir(self._cache_dir) if f.endswith(".xml")]
        for f in filelist:
            os.remove(os.path.join(self._cache_dir, f))
        filelist = [f for f in os.listdir(self._cache_dir) if f.endswith(".xml")]
        return len(filelist) == 0

    def getCachedImage(self, project, request, key):
        m = hashlib.md5()
        paramMap = request.parameters()
        urlParam = "&".join(["%s=%s" % (k, paramMap[k]) for k in paramMap.keys()])
        m.update(urlParam.encode('utf8'))

        if not os.path.exists(os.path.join(self._tile_cache_dir, m.hexdigest() + ".png")):
            return QByteArray()

        img = QImage(m.hexdigest() + ".png")
        with open(os.path.join(self._tile_cache_dir, m.hexdigest() + ".png"), "rb") as f:
            statusOK = img.loadFromData(f.read())
            if not statusOK:
                print("Could not read or find the contents document. Error at line %d, column %d:\n%s" % (errorLine, errorColumn, errorStr))
                return QByteArray()

        ba = QByteArray()
        buff = QBuffer(ba)
        buff.open(QIODevice.WriteOnly)
        img.save(buff, 'PNG')
        return ba

    def setCachedImage(self, img, project, request, key):
        m = hashlib.md5()
        paramMap = request.parameters()
        urlParam = "&".join(["%s=%s" % (k, paramMap[k]) for k in paramMap.keys()])
        m.update(urlParam.encode('utf8'))
        with open(os.path.join(self._tile_cache_dir, m.hexdigest() + ".png"), "wb") as f:
            f.write(img)
        return os.path.exists(os.path.join(self._tile_cache_dir, m.hexdigest() + ".png"))

    def deleteCachedImage(self, project, request, key):
        m = hashlib.md5()
        paramMap = request.parameters()
        urlParam = "&".join(["%s=%s" % (k, paramMap[k]) for k in paramMap.keys()])
        m.update(urlParam.encode('utf8'))
        if os.path.exists(os.path.join(self._tile_cache_dir, m.hexdigest() + ".png")):
            os.remove(os.path.join(self._tile_cache_dir, m.hexdigest() + ".png"))
        return not os.path.exists(os.path.join(self._tile_cache_dir, m.hexdigest() + ".png"))

    def deleteCachedImages(self, project):
        filelist = [f for f in os.listdir(self._tile_cache_dir) if f.endswith(".png")]
        for f in filelist:
os.remove(os.path.join(self._tile_cache_dir, f))
        filelist = [f for f in os.listdir(self._tile_cache_dir) if f.endswith(".png")]
        return len(filelist) == 0

And the way to add it to the QGIS Server cache manager.

servercache = PyServerCache(server_iface)
server_iface.registerServerCache(servercache, 100)