Openlayers 3 - how to keep features from disappear when outside of visible view?

Question

I have gps coords features on a map and I want to add a line that shows the route of the feature , so I created an icon with long arrow (40px X 600px) I've noticed that the moment I pan the map and the feature is outside of the visible area , it disappears (although the icon should still be visible)

How can I keep the features from disappear outside the visible map ?

Answer 1

ol.layer.Vector has a property called renderBuffer. This property will prevent the icons from disappearing if you set this to the pixel value of the longest side of your icon images, 600px in your example:

var vectorLayer = new ol.layer.Vector({
  source: vectorSource,
  renderBuffer: 600 // value in pixels
});

Demo code: https://plnkr.co/edit/R4qs5cmgEdYQCSu9c3gn -- Try changing the renderBuffer value in script.js, line 44 to see the result.

Answer 2

This is perhaps not a correct solution, but setting useSpatialIndex to false on a VectorSource seems to allow a custom Style.renderer function to avoid disappearing when the feature geometry is out of view.

Disabling useSpatialIndex has ramifications (see the VectorSource docs), so it's best to use in a limited way.

Perhaps another method is to do something similar to the Graticule implementation, with a custom loader function.