Map projection and forced interpolation

I wish this helpful for you Use homogeneous coordinates, which can be linearly interpolated in screen space: http://www.cs.unc.edu/~olano/papers/2dh-tri/

To fix this issue In twig when you just use foo.bar, foo may be an array (in this case twig expects a key bar), or an object, whereas it expects either a accessible property bar, a methods getBar(), and I guess something I forgot. However, the point is, that twig tries to resolve the kind of access itself and you can throw in, whatever you like (beside that it must obviously in a form of structured data). If you use a specific access method, you take the ability to guess from twig: When you call foo.bar() it's obviously a method. (Must say, that I never heard of "forced lookup" :X)

hope this fix your issue Got it. And it was as stupid a mistake as expected: I was reinitializing my zBuffer each frame...
Usually it's what you should do, but in my case, each frame (ie call of my Painting() function) adds details to the same frame (ie drawed static scene from a constant given point of view).

pixelY = dY / dZ * minDim + canvasHeight +.5|0,
pixelX = dX / dZ * minDim + canvasWidth +.5|0,
canvasInd = pixelY * canvasWidth*2 + pixelX;
if (dZ > 0 && (!zBuffer[canvasInd]  || (dZ < zBuffer[canvasInd]))) {
    // We draw the point and update the zBuffer.
}

help you fix your problem Unfortunately this is not available yet as part of the aggregation framework. However, according to this JIRA ticket, it is currently "planned by not scheduled". The only way of doing this currently is by using the map/reduce functionality. If you want to go ahead and use that, it would mean doing something as follows:
Map each document by _id and emit the appropriate key. Since there will be only one value per key, the reduce function will not get called, but you still need to initialise the variable you use for the reduce function. You can use an empty function or an empty string. Run map/reduce, saving the results in a collection of your choice.

var mapper = function() {
    var typeValue = this.types[this.default];
    emit(this._id, typeValue);
};
var reducer = "";

db.types.mapReduce(mapper, reducer, { out : "results" } );

> db.results.find();
{ "_id" : ObjectId("53d21a270dcfb83c7dba8da9"), "value" : 1 }

var mapper = function() {
    var typeValue = this.types[this.default],
        typeKey = "types." + this.default;

    emit(this._id, { key : typeKey, val : typeValue } );
};   

> db.results.find().pretty();
{
    "_id" : ObjectId("53d21a270dcfb83c7dba8da9"),
    "value" : {
        "key" : "types.x",
        "val" : 1
    }
}

it fixes the issue This looks like a bug to me. @ResMar's assertion that the extents aren't in a projection is incorrect. According to the documentation for get_extent():