In a noninvasive system for detection/measurement of glucose and other analytes in a medium such as tissue, illumination is directed to the medium and corresponding radiation from the medium is collected. Spectral energy changes associated with fragment(s)/feature(s) obtained from the collected radiation are determined using collision computing. Such spectral energy changes generally represent analyte concentration. The collection of radiation and/or illumination is controlled either to target a particular volume of the medium or such that the spectral energy changes become directionally monotonic with respect to analyte concentration, or both. The collection parameters include: duration of collection, location and/or a size of a collection spot on the medium surface, and angle of a collector relative to the medium surface. The illuminated and/or collection spots may be treated to improve accuracy of analyte measurement.