2 1/2 D visual servoing: a possible solution to improve image-based and position-based visual servoings

We describe in this paper potential problems that may appear in image-based visual servoing when the initial camera position is far away from its desired position. We show by concrete examples that local minima or a singularity of the image Jacobian can be reached during the servoing. We then recall recent results obtained to avoid these drawbacks. It consists in combining visual features obtained directly from the image, and position-based features. This approach, called 2½D visual servoing, also provides supplementary advantages with regard to the mean the features are combined with