1. A measurement device comprising: an image capturing unit including a photoelectric unit and configured to capture multiple images corresponding to respective multiple different photoelectric areas of the photoelectric unit, the photoelectric unit photoelectrically converting incident light; multiple reflecting units arranged at different positions, each of the reflecting units being positioned to reflect light traveling from a projection area between a projection surface, on which a projection image is to be projected, and the measurement device off a reflecting surface of the reflecting unit; changing units, each of the changing units being provided for one reflecting unit of the multiple reflecting units and configured to change an image capture angle of the one reflecting unit; a light condensing unit configured to condense each of reflected light beams reflected off the different reflecting units to a corresponding one of the different photoelectric areas of the photoelectric unit; an obtaining unit configured to obtain the multiple captured images corresponding to the respective multiple photoelectric areas and image capture angles of the reflecting units, each of the image capture angles being an angle at which one of the captured images is captured; a selection unit configured to select, from the multiple captured images, two or more images in each of which a measurement subject is captured; and a calculation unit configured to calculate a position of the measurement subject in a 3D space based on the selected two or more captured images and the image capture angles corresponding to the respective two or more captured images.