OPTICAL SURVEYING INSTRUMENT

The invention relates to optical surveying such as in building construction, road construction, landscaping and similar. A first image sensor obtains in a first wavelength range a first image of a scene within a field of view captured by an optical arrangement such as a telescope. A light emitter emits light in a second wavelength range and a second image sensor obtains a second image of the field of view in the second wavelength range. A target position of a reflecting target is found in the first image by detecting a known image pattern of the reflecting target in the first image. A region of interest in the second image is then a defined based on the identified target position in the first image, for detecting a reflector position of a reflector of the reflecting target in the region of interest. With the invention it becomes possible to improve the identification of a reflective target at reduced processing time, even if reflections from other objects than the reflective target are present.