Thank you all for your comments. ^^ In response to Peenut2k7, heightmaps are more or less provided for you in-game in the form of the minimap, which appears in the upper left of the screen. Just run your character or camera to a position where all of the heightmap is visible, press print screen, and then it'll be available in your FeralHeart's screenshots folder. All you have to do is select the area containing the heightmap and enlarge it to 513 x 513. Of course, since the minimap is so small, there will be some quality loss when resizing - but that detail can be painted back in afterwards.
In response to Jennifer, many thanks. ^^ I'm inclined to agree with you; it's a shame Kovu never implemented shadows or bloom into FeralHeart.