1. An apparatus for measuring a surface, the apparatus comprising: a portable housing, a projection assembly mounted in the portable housing and projecting an image on the surface, a camera mounted in the portable housing and configured to capture the projected image as measurement data, and a processor controlling the projection assembly and the camera and receiving the measurement data from the camera, where the projection assembly comprises an image generator, a light source, and a train of projection optics, the projected image comprises a measurement-pattern image or a result-image, and the processor derives a characteristic of the result-image by analyzing the measurement data corresponding to the measurement-pattern image.