Layer.getExtent() returns undefined when working with a Layer sourced by a GPX file

the problem

When trying to work with a Layer sourced by a GPX file, I had a hard time trying to figure out why gpxLayer.getExtent() was undefined… until I found out that gpxLayer.getSource().getExtent() was the right way to get its extent.

the proposed solution

I think it would be easier for newcomers if a method like Layer.getExtent() always return the correct extent, no matter what is behind the scenes, whether it is a Tile layer, a Vector layer or an Overlay layer.

some sample code

// this is the code that works
map.getView().fit(buffer(gpxLayer.getSource().getExtent(), 1000))

// this is the code that doesn't work nowadays
map.getView().fit(buffer(gpxLayer.getExtent(), 1000))

[ahocevar]

The layer’s getExtent() function returns the layer extent, if you specified one to restrict the visible area of the layer. This is documented in https://openlayers.org/en/latest/apidoc/module-ol_layer_Vector-VectorLayer.html#getExtent.

This is because in OpenLayers, the Layer is a lightweight container that configures things that influence the way the layer is rendered (e.g. styles, rendered extent, etc.). Whereas the Source represents the underlying data. So to get the extent of the data, you’ll need to ask the source for the extent.

[bmnds]

I see… I will close this issue then.

But maybe this explanation could be added to VectorLayer.getExtent docs.