1. A method of generating compact feature descriptors for transmission over a communications network in a mobile visual search system, the method comprising: receiving an uncompressed three-dimensional feature descriptor; performing zero-thresholding on the uncompressed three-dimensional feature descriptor to generate a zero-threshold-delimited three-dimensional feature descriptor; quantizing the zero-threshold-delimited three-dimensional feature descriptor to generate a quantized three-dimensional feature descriptor; and coding the quantized three-dimensional feature descriptor to generate a compact three-dimensional feature descriptor for transmission over the communications network in the mobile visual search system.