KmlDataSource: how to use texture filtering?

Hello, the KmlDataSource overlay I use looks bad (see picture). How can I use
texture filtering to improve the visual of the map?

I found something like “Cesium.TextureMinificationFilter.LINEAR” but I don’t know where to put it.

This is how the result SHOULD look like (I faked this picture with Gimp). Notice that the qualtiy of the overlay map is much better.