Photogrammetry with the smartphone
Have you ever wished that you could easily transfer a real object into a digital file? The technology is here, but many people simply don’t have access to high-end 3D modeling that can perform object reconstruction. However, there is another, much cheaper way to create 3D models corresponding to real-world objects using your smartphone.
With the recent advancements in computer vision, spatial computing devices (VR/AR headsets), aerial capture technology, photogrammetry is becoming more accessible to game developers, photographers, as well as VFX artists. It can also be performed by using a smartphone. Here are some of the smartphone requirements:
- Camera (preferably with a high megapixel count, iPhone 7plus also possible);
- Photogrammetry software.
Choosing the subject
You can divide photogrammetry into 2 types of subjects: interior captures and exterior. There isn’t any real difference in how the subjects get processed and created into 3D, but how you take pictures.
Interior subjects (inside out photography)
When it comes to capturing the objects, the best tools at your disposal will be:
- A camera like a DSLR that can handle lower lit situations(new smartphones can be decent at handling these situations as well);
- Tripod (if the space is actually really dark and you need longer exposure times);
- Tons of overlapping pictures.
Exterior captures (capturing singular objects)
Exterior captures can be somewhat easier, because they’re harder to mess up. You have a subject that you can walk (or fly) around and take a overlapping photos along that path. The scale of the subjects can vary. You can capture everything from the exterior of a building to something as small as a pinecone. It all depends on what cameras you have access to.
How photogrammetry works?
Photogrammetry is a process that estimates the three-dimensional coordinates of surface points using pictures of a single physical object taken from different angles. You take a bunch of pictures of the object from all the possible directions and use these photos as an input for a specialized software. The software will look for features that are visible in multiple pictures and try to identify from which point was the picture taken. Knowing the camera positions and orientations, it creates a 3D point that corresponds to the 2D feature on the photo (basically a pixel).
Photogrammetry based software is one of the simplest and fastest ways of getting high-quality 3D models. It is often applied to create realistic scales of objects utilizing a series of overlapping or superimposed photographs. 3D modeling technology makes visualization process faster and easier than ever before.
If we have at least 3 photos taken from a different angle, we can already reconstruct the 3D model of the object. However, the more pictures, the more likely the 3D model will be realistic. Let’s talk about taking pictures more.
Taking pictures for photogrammetric software
You’ll want to capture with your smartphone at least 20 pictures. During testing, one often shot 50-80 pictures to capture every detail. Keep in mind, that some pictures might get discarded if the program doesn’t find enough similarities with other pictures. Here are some tips of taking the best photos possible:
- Move around the target object in circles. Do not move the object or its surroundings between pictures.
- Overlap! You want to have each part of the model captured by at least 2 pictures. Ideally, you’d have about 60-80% overlap in succeeding pictures.
- Avoid hard shadows, use diffuse lighting or take the pictures outside on a semi-cloudy day.
- The object should make a significant portion of each image.
- Avoid moving targets (e.g. pets, unless they are sleeping).
- Avoid very glossy or transparent targets. Ideal targets for photogrammetry are textured or rough items (statues). If it’s an option, you can cover glossy or transparent objects with powder (flour) to avoid reflections. Or cover the glossy surface with a painters tape. Advanced users can also capture a video of the target and then convert it into individual frames. In this case, keep the shutter speed high (e.g. 1/80) to avoid blurry frames.
Just like any other 3D modeling technique, the final look using the smartphone could be not perfect – it needs specific features and higher quality camera to make the object look more realistic. Therefore, some areas might be missing details, flat surfaces may not turn out completely flat, we can not always avoid the shadowing or the darkness.
Photogrammetry based software can outperform 3D scanners. You can recreate huge objects that would be nearly impossible to capture with traditional 3D scanning tools. It’s extremely affordable and chances are that you already have everything you need for photogrammetry – a camera (smartphone) and somewhat powerful PC.