In this paper we present two methods to geometrically calibrate a video projector using a markerless  planar surface. The first method assumes a partial knowledge on the camera parameters whereas the  second method consists in an auto-calibration method with no assumption on the parameters of the  camera. Instead, the auto-calibration is performed by identifying a roughly fronto-parallel pose  of the camera w.r.t the projection surface.
The fact that camera calibration is not needed increases the usability of the methods  and at the same time eliminates one potential source of inaccuracy, since errors in  the camera calibration would otherwise inevitably propagate through the projector  calibration. Not using a printed pattern as most existing methods do is another   gain in accuracy and ease of use.
As depicted by our experiments,both methods enjoy a good stability and give good   results when compared against existing  methods.

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