Agisoft Metashape is a stand-alone software product that performs photogrammetric processing of digital images (aerial and close-range photography, satellite imagery) and generates 3D spatial data to be used in GIS applications, cultural heritage documentation, and visual effects production as well as for indirect measurements of objects of various scales.
This section explains the general principles of taking and selecting pictures that provide the most appropriate data for 3D model generation.
Make sure you have studied the following rules and read the list of restrictions before you get out for shooting photos.
- Resolution. Use a digital camera with reasonably high resolution. It is also recommended to take photos in the max possible allowed resolution.
- Focal length. The best choice for a common frame camera is 50 mm focal length (35 mm film equivalent) lenses. It is recommended to use the focal length from 20 to 80 mm interval in 35 mm equivalent.
- Lens distortion. The distortion of the lenses used to capture the photos should be well simulated with the camera model used in the software. Generally, Brown's distortion model implemented in Metashape works well for frame cameras. However, since fisheye and ultra-wide angle lenses are poorly simulated by the mentioned distortion model, it is crucial to choose the proper camera type in the Camera Calibration dialog prior to processing such data - the software will switch to the appropriate distortion model.
- ISO should be set to the lowest possible value, otherwise, high ISO values will induce additional noise to images and some details may be lost.
- Aperture value should be high enough to result in sufficient focal depth: it is important to capture sharp, not blurred photos (recommended f/stop values: f/8 - f/11).
- Shutter speed should not be too slow, otherwise, blur can occur due to slight movements. If lighting conditions are poor, consider using a tripod and a longer shutter speed.
- Using RAW data losslessly converted to the TIFF files is preferred, since JPG compression may induce unwanted noise to the images. Although for common projects JPG images with higher quality settings (and lower compression) are acceptable.
The shooting scenario depends on the object of the survey (this is a forest area, a detached building, a monument, etc.). Separate articles describe the main recommendations for:
- Aerial survey tips
- Terrestrial shooting scenario
- Close - range objects scanning
- Full body/head scanning capture tips
- Suggested scenario for photo shooting an interior
- Underwater survey image capture tips
We recommend following these guidelines:
- Overlap. In the case of aerial photography, the overlapping requirement can be put in the following numbers: 60% of side overlap + 80% of forwarding overlap.
- A number of photos: more than required is better than not enough. Later on, you can disable or skip excessive images.
- Effectively use the frame size. Each photo should effectively use the frame size: the object of interest should take up the maximum area. In some cases, portrait camera orientation should be used.
- Lighting. Good lighting is required to achieve a better quality of the results, yet reflections and glares should be avoided. It is recommended to remove sources of light from camera fields of view. Also, avoid using flash - plain diffuse lighting is preferred.
- "Blind-zones". A number of "blind-zones" should be minimized since Metashape is able to reconstruct only geometry visible from at least two cameras.
- Georeferenced model:
- In the case of aerial photography and demand to fulfill georeferencing task, even spread of ground control points (GCPs) (at least 10 across the area to be reconstructed) is required to achieve results of the highest quality, both in terms of the geometrical precision and georeferencing accuracy.
- Metashape is able to complete the reconstruction and georeferencing tasks without ground control points, too, basing on the loaded coordinates of the camera locations, providing that they do not lay on the same line.
Working with reference data, markers, and scale bars is only available in the Professional version of the program.
- Markers. If you are planning to carry out any measurements based on the reconstructed model, do not forget to locate at least two markers with a known distance between them on the object. Alternatively, you could place a ruler within the shooting area.
- Texture. Care about the object's texture and invent tricks to avoid plain/monotonous and glittering/reflective surfaces. For example: in case you are to shoot a human leg, put a finely textured sock on it before; if your target object is a car, spread some talc powder (or anything similar) over it to change it from glittering to the dull surface.
- Metashape can process only unmodified photos as they were taken by a digital photo camera. Processing the photos which were manually cropped or geometrically warped is likely to fail or to produce highly inaccurate results. Photometric modifications (such as brightness or contrast adjustment) do not affect reconstruction results, providing that no hard filters are applied that could remove minor details on the images, such as Gaussian/blur filter, for example. You can find an example of the workflow for building a 3D model in our article - 3D model reconstruction.
Scanned aerial images with fiducial marks are supported in the Professional edition only.
- Camera type. If a data set was captured with a fisheye, spherical, or cylindrical camera type, the appropriate camera sensor type should be selected in the Metashape Camera Calibration dialog (Tools > Camera Calibration ) prior to processing:
- Fixed lenses are preferred. If zoom lenses are used - focal length should be set either to maximal or minimal value during the entire shooting session for more stable results, for intermediate focal lengths separate camera calibration groups should be used (usually distributed automatically based on EXIF data, but can be manually split into groups in the Tools Menu > Camera Calibration dialog).
- EXIF data. Metashape calculates initial values of sensor pixel size and focal length parameters based on the EXIF data. The better the initial approximation of the parameter values is, the more accurate autocalibration of the camera can be performed. Therefore, reliable EXIF data is important for accurate reconstruction results.
- Lack of EXIF data. 3D scenes can also be reconstructed in the absence of the EXIF data. In this case, Metashape assumes that focal length in 35 mm equivalent equals to 50 mm and tries to align the photos in accordance with this assumption. If the correct focal length value differs significantly from 50 mm, the alignment can give incorrect results or even fail. In such cases, it is required to specify initial camera calibration manually (Tools > Camera calibration). Read more for camera calibration in the User Manual.
- DON'T crop or geometrically transform images. Metashape operates with the original images. So DON'T crop or geometrically transform (i.e. resize or rotate) the images, otherwise, it will affect the autocalibration procedure - the process of the automatic estimation of calibration and distortion parameters.