An OAOA measurement system uses optical elements to converge incoming light from multiple sources onto an FPA as respective crosshair patterns made from lines which are oblique with respect to the FPA's axes, such that each pattern's location indicates the angular position of its corresponding source. The optical elements are arranged such that each crosshair's center point is at least twice as bright as the lines which form the crosshair's arms. The position of each crosshair is interpolated by defining regions around each arm of one of the crosshairs, determining the points of peak intensity in each row or column within each region, and curve-fitting the points to define each arm. Multiple crosshair patterns are accommodated by assigning a small magnitude value to each pixel of a defined arm, and then repeating the interpolation process for another crosshair.