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In QGIS, there is a plugin to insert a OSM cycle map layer, that brings as an image from http. But I can't convert this OSM Plugin layer to a raster image. I can't even imagine how to get the contour lines that are showing by the cycle map as a vector.

Is this possible?

If is not possible through OSM, there is another open resource to get this?

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Well re-vectorization doesn't seem to be the key to a good solution here.

As @Andre points out, the OSM Openlayers plugin just adds a raster layer. You can pick an OSM map (as cyclemap) that is postprocessed to include height contour lines, but in general height data (DEM) aren't part of the (current) OSM data model.
So the contour lines are derived from the SRTM height dataset and transformed and local imported as it can be rendered with the default OSM renderers as Mapnik: https://wiki.openstreetmap.org/wiki/Contour

To make use of the contour lines with QGIS, you might want to download them seperately as shapefile and add them as vector layer on top of your OSM raster layer.

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The Openlayers plugin does not deliver a raster image, but a bunch of 256x256 tiles instead.

The raster to vector converter can not handle these tiles. It would be possible to prefetch all tiles you need, then build a vrt around them, and vectorize that. But that would be unnecessary much work.

The contours come from NASA SRTM mission, and there are many softwares around to gather contour lines directly from that. One of them is QGIS ;-)

There are other sources like ASTER and http://www.viewfinderpanoramas.org that have ruled out the bugs in the SRTM data.

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