I need help choosing a game engine for a very specific task

I need a 3D engine for a very specific task in Artificial Intelligence, and I'd like some input.

The first part is the trivial one - basically, all I need is a FPS engine (3rd person would be good, too), such that it allows me to navigate a room and interact with objects (if you have Java and Windows, I'm looking for something similar to the Give Challenge, but a little more up-to-date). Physi开发者_高级运维cs would be nice, but is not a must.

Now, the non-trivial part would be: I need to impose a virtual grid over this room, such that at any moment I can say "the player is located at B5 - now he moved to B6", and so on. I need to redirect this information to another system (namely, one which will give the player instructions about what to do) and, at the same time, send messages to the player, so I must be able to have a single point through which the game logic passes through; also, I'd love not having to write my own collision detection and such.

So far, I've tried:

• the Source SDK: it seems a little overkill (since I'm not really planning to shoot anyone, at least half the code base is useless to the task), and since I'm not really a Windows developer, I'm spending too much time with the "easy" stuff (such as getting VS up and running). Plus, cross-platform would be really nice.
• Blender game engine: while this worked decently, the interaction model seems a little weird, and some easy stuff (such as making sure the camera stays inside the scene or showing the mouse on screen) gets too weird too soon.
• Crystalspace 3D: I've tried their demos, but it looks a little old-fashioned, and since that was one of the problems of previous engines (it's easier to get volunteers when your game looks nice) I'd like to try something else.

Now, maybe I'm asking a little too much for a single software, but I'd love some input. Can anyone suggest me an alternative? Or should I give one of the previous ones a second chance?

Try the UDK. All of the things you request are present, and it's free for personal/noncommercial projects. Here are some highlights:

• Modern looking. The UDK features an intuitive-ish visual material design system, post-processing effects, Scaleform Gfx UIs from Autodesk, and more.
• A visual scripting interface called Kismet that can control gameplay elements, the camera, and more.
• UnrealScript, a scripting language similar in syntax to C, C++, Java, that gives you the ability to extend existing functionality or create your own.
• Comprehensive documentation available on UDN.
• Lots of community support outside of Epic, in places such as Polycount, Eat3d, 3dbuzz, and more.
• Basically, "and more".

If what you're looking for is a professional, free (as in beer) engine that will allow you to focus primarily or solely on your differentiating gameplay features, Epic has set the bar high.