[libGDX] How to draw an outline around sprite when behind another image

Hello

I’m developing an Isometric game in libGDX with Tiled maps. I’ve set different layers for different things in Tiled. Basically, i want to draw an outline around the player sprite(texture region) when it goes behind some Tiled tiles. It’ll help to see the player when it is behind a large object. So,

• How to detect the player sprite is behind some tiles or an image? (All objects are drawn in Tiled)
• How to draw an outline around the player sprite which is visible through the blocking object?