Close-range objects scanning
Modified on: Wed, 9 Dec, 2020 at 11:46 AM
- Any restrictions on objects I can "photoscan"? Avoid untextured, highly reflective and transparent objects. The data set will lack reliable information for the reconstruction procedures, if the scanned surface doesn't have any distinguishable features, such as irregular color or material texture pattern, since photogrammetric processing is based on the feature points of the object to be found on the photos.
- Which lenses to choose: fixed or zoom? what focal length is preferable? It is better to use fixed lenses with focal length from 20 mm to 80 mm (in 35 mm equivalent). If zoom lenses have to be used for the project, it is strongly recommended to fix the lenses mechanism with a sticky tape, for example. If wide angle lenses (focal length less than 15-20 mm) have to be used, 'fisheye' value should be selected in the Camera type field of Camera Calibration dialog prior to starting the Align Photos operation. But wide angle lenses may still introduce inaccuracies to the processing results.
- Aperture. Shallow focal depth causes blurred areas on the images, especially in case of an object with complex geometry. Sharp photos are a prerequisite for quality processing results. So aperture value should be high enough to result in sufficient focal depth. We recommend f/stop values: f/8 - f/11.
- ISO. It is recommended to use minimal possible ISO in order to minimize the image noise.
- Lighting. It is recommended to shoot in bright ambient lighting conditions. The position of the light source during the shooting process, as well as the position of the target object relative to the direction of light should not be changed. Stability of the alignment process may be badly affected by the variations in brightness of the object points.
- Lighting in a turntable scenario. It is quite a common scenario for the small assets scanning: white box, controlled environment, turntable and fixed camera mount. When following this scenario, please remember to use diffuse light rather than a point light source in order to avoid discrepancies on the final texture of the 3D model. Good lighting is required to achieve quality results of photogrammetric processing, yet the reflections should definitely be avoided, so using flash is not recommended. Last but no least recommendation is to remove all sources of light from the camera field of view.
- Masking tool for turntable scenario. If a turntable scenario was used to capture source imagery data, then the first pre-processing operation to be performed in Metashape is Apply masks. Shoot a "blank frame" - a set of images of the background without object itself - for automated masking process (more details about creating masks from background see in the Masking from background solution). This will allow to easily exclude all background points from processing.
- Shooting in macro mode. Using tripod and remote control will help to avoid harmful camera shake effect when shooting in macro mode.
- Unwanted objects on the images to be processed. It is recommended to plan your shooting scenario in such a way so that unwanted foregrounds, backgrounds, as well as moving objects can be avoided on the images. If the photos do include some unwanted objects / background, it is recommended to use Masking tool in Metashape to mask those objects out and, thus, exclude them from the processing. It will a) help to avoid ghosting effect when generating texture for the model; b) save hardware resources thanks to processing only useful data; and c) allow processing algorithms to work with meaningful range of data, which is important, for example, when filtering outliers or using a limited number of polygons to reconstruct a mesh model of the scene of interest.
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