1.4. Taking Photographs Without the mat

Using the calibration mat is the easiest way to determine the camera orientation and position and create 3d models from the photographs. However in certain situations this is not practical - e.g. the photos have been supplied by someone else or the object is too large to place on a mat (for example a statue or car).

In 3DSOM Pro version 3 we have included an alternative system which relies on user supplied "markers" provided for each image. We have created a simple interface that allows users to place these markers in the images with a minimum of effort. Once the markers are present, camera estimates are automatically calculated and the software can then create a wireframe and textured mesh in the usual way.

Suitable photos

The photos should be taken around the object from around 10 to 20 directions. Make sure there are suitable easily identifiable features in the images. These must be fixed points that you can see in several images such as the corner of a label, sharp corner, centre of a small "blob" or other feature with a precise position. You can rotate the object and keep the camera fixed but if you do so, you will need to mark features that lie on the object and not the surrounding backdrop.

You can use photos taken with a standard digital camera in JPEG or TIFF format. The software will need to extract special EXIF image tags from the image files to determine the camera focal length. Most digital cameras store this information. However if the image has been processed or cropped the information may be missing (do not crop your images). If you have kept the zoom setting fixed on your camera and the EXIF tags are missing, you will be given the opportunity to manually enter the values.

Where possible the photos taken without a calibration mat should follow the previously described guidelines for images with the mat — a backdrop and stand should ideally be used to help separate the object shape from the background.

The Creating a 3D model from photographs without using a calibration mat tutorial descibes how to process photos taken without a calibration mat in 3DSOM Pro to create a 3D model.