A method for joint visual object detection and object mapping to a 3D model, the method being performed by an image processing device, the method comprising: obtaining a first sequence of digital images of a scene (400, 510) as captured by a first image capturing unit, and obtaining a second sequence of digital images of the scene (400, 510) as captured by a second image capturing unit, wherein the second sequence of digital images is time-wise synchronized with the first sequence of digital images by being captured time-wise in parallel with the first sequence of digital images, wherein the first image capturing unit has a narrower field of view than the field of view of the second image capturing unit, and wherein the first image capturing unit and the second image capturing unit have a known spatial relation; and performing joint visual object detection and object mapping to the 3D model by: extracting (S108a) a set of objects (410a:410d, 520) from both the first sequences of digital images and the second sequence of digital images by performing visual object detection on both the first sequence of digital images and the second sequence of digital images; mapping (S108b) the extracted set of objects (410a:410d, 520) to the 3D model in accordance with the second sequence of digital images and the known spatial relation, and thereby registering the scene (400, 510) to the 3D model; and the method being characterised in: providing, as a result of how many objects (410a:410d, 520) are detected either in the first sequence of digital images or in the second sequence of digital images, an indication to move the image capturing units closer towards, or farther from, the scene (400, 510). obtaining a first sequence of digital images of a scene (400, 510) as captured by a first image capturing unit, and obtaining a second sequence of digital images of the scene (400, 510) as captured by a second image capturing unit, wherein the second sequence of digital images is time-wise synchronized with the first sequence of digital images by being captured time-wise in parallel with the first sequence of digital images, wherein the first image capturing unit has a narrower field of view than the field of view of the second image capturing unit, and wherein the first image capturing unit and the second image capturing unit have a known spatial relation; and performing joint visual object detection and object mapping to the 3D model by: extracting (S108a) a set of objects (410a:410d, 520) from both the first sequences of digital images and the second sequence of digital images by performing visual object detection on both the first sequence of digital images and the second sequence of digital images; mapping (S108b) the extracted set of objects (410a:410d, 520) to the 3D model in accordance with the second sequence of digital images and the known spatial relation, and thereby registering the scene (400, 510) to the 3D model; and the method being characterised in: providing, as a result of how many objects (410a:410d, 520) are detected either in the first sequence of digital images or in the second sequence of digital images, an indication to move the image capturing units closer towards, or farther from, the scene (400, 510). extracting (S108a) a set of objects (410a:410d, 520) from both the first sequences of digital images and the second sequence of digital images by performing visual object detection on both the first sequence of digital images and the second sequence of digital images; mapping (S108b) the extracted set of objects (410a:410d, 520) to the 3D model in accordance with the second sequence of digital images and the known spatial relation, and thereby registering the scene (400, 510) to the 3D model; and the method being characterised in: providing, as a result of how many objects (410a:410d, 520) are detected either in the first sequence of digital images or in the second sequence of digital images, an indication to move the image capturing units closer towards, or farther from, the scene (400, 510).