Photos suitable for 3D model reconstruction in Metashape can be taken by any digital camera (both metric and non-metric), as long as you follow some specific capturing guidelines. This section explains general principles of taking and selecting pictures that provide the most appropriate data for 3D model generation.
IMPORTANT! Make sure you have studied the following rules and read the list of restrictions before you get out for shooting photos.
- Use a digital camera with reasonably high resolution (5 MPix or more).
- The best choice for common frame camera is 50 mm focal length (35 mm film equivalent) lenses. It is recommended to use focal length from 20 to 80 mm interval in 35 mm equivalent.
- If a data set was captured with fisheye lens, appropriate camera sensor type should be selected in 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 to 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 basing on EXIF data, but can be manually split into groups in the Tools Menu > Camera Calibration dialog).
- Care about object's texture and invent tricks to avoid plain/monotonous and glittering surfaces. For example: in case you are to shoot a human leg, put a finely textured sock on it before; if you target object is a car, spread some talc powder (or anything similar) over it to change from glittering to dull surface.
- Using RAW data losslessly converted to the TIFF files is preferred, since JPG compression may induce unwanted noise to the images. Although for common project JPG images with higher quality settings (and lower compression) are acceptable.
- Take images at maximal possible resolution.
- 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.
- 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.
NOTE: Generally, spending some time planning your shot session might be very useful.
- Number of photos: more than required is better than not enough. Later on you can disable or skip excessive images.
- Number of "blind-zones" should be minimized since Metashape is able to reconstruct only geometry visible from at least two cameras.
- In case of aerial photography the overlap requirement can be put in the following numbers: 60% of side overlap + 80% of forward overlap.
- Each photo should effectively use the frame size: object of interest should take up the maximum area. In some cases portrait camera orientation should be used.
- Do not try to place full object in the image frame, if some parts are missing it is not a problem providing that these parts appear on other images.
- Good lighting is required to achieve better quality of the results, yet blinks should be avoided. It is recommended to remove sources of light from camera fields of view. Avoid using flash - plain diffuse lighting is preferred.
- 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.
- In 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 highest quality, both in terms of the geometrical precision and georeferencing accuracy.
- Metashape is able to complete the reconstruction and georeferencing tasks without GCPs, too, basing on the loaded coordinates of the camera locations, providing that they do not lay on the same line. NOTE: working with reference data, markers and scale bars in only available in the Professional version of the program.
Modifications of photographs
- 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. NOTE: Scanned aerial images with fiducial marks are supported in Professional edition only.
- Metashape calculates initial values of sensor pixel size and focal length parameters based on the EXIF data. The better 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 scene 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 User Manual.
- 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 proper camera type in Camera Calibration dialog prior to processing of such data - the software will switch to the appropriate distortion model.