how to use your cellphone for 3D scanning
Contributed by Chris, Arrival 3D scanning technician and CAD modeler, August 13, 2018.
Can I use my cellphone camera for 3d scanning?
The image quality on many cell phone cameras is sufficient for 3D reconstruction with photogrammetry software. There are free or low cost photogrammetry applications that can create 3D files as point clouds or meshes, with full color. While the results won’t have the quality, accuracy, or ability to capture live subjects, like 3D scanners costing tens of thousand of dollars, cell phone photogrammetry can produce results that are potentially useful, nevertheless.
How many pictures do I need to take?
Worthwhile results will require a bit of procedure in the picture taking, as taking a bunch of images randomly is less likely to produce usable results. Roughly 60 to 100 pictures are needed to cover an object completely and produce something that results in a recognizable form, even more, if smaller details are needed. With a bit of practice, one could take a few hundred pictures in 5 to 10 minutes that will register properly in a photogrammetry application.
What are some techniques I need to keep in mind for 3d scanning?
Evenly spacing the distance between images, as well as consistently changing the angle between the images will yield better registration results. The goal is to create a set of images that covers the object or area in a regular grid. The area of each image must overlap significantly with adjacent images, and the angle difference between images should not be more than approximately 20 degrees or so. After doing this several times, one can get a good “feel” for the process so that it become automatic with repetition.
The complexity of the object also relates to the quality of the result; anything causing the autofocus to change between images is problematic. A wagon wheel, for example proved to be a poor subject because the phone camera would not consistently focus on the spokes, many time focusing on the ground behind. Poor focus makes the image unsuitable in calculating the 3D form.
Also critical is lighting, with bright, even illumination being the ideal. Outdoor images are best taken on overcast days where possible. High contrast lighting will typically result in holes in shadow areas in the resulting object. Reflective, shiny, or transparent surfaces will also result in holes or incomplete surfaces, although in some cases a dulling spray, or dusty coating can help.
creating a model
Photogrammetry software cannot interpret dimensions automatically from images. Therefore, if there is any desire to produce a 3D model that relates to real world dimensions, it is necessary to capture references in the photos that are at known distances, or are physically measured (ie tape measure or similar), to scale the resulting model in the software.
Your cellphone won’t replace the professional 3D scanning hardware. However, you do have it with you everywhere you go and it can capture 3D information from the world around you. It could give useful results either for fun, reference, or perhaps work, with a little bit of knowledge and effort.