3D is in! 3D movies and computer games are increasingly popular, but the technology can be used for more than just cool special effects – scientists can get a lot of information from a simulated 3D object. But it can be hard making these 3D objects. To help, Dr Chuong Nguyen from CSIRO is developing a simple system of capturing the shapes and colours of insects.
The first step is to take a lot of 2D photos of the insect. They are taken from lots of different angles, to capture as much detail as possible. A calibrating pattern is placed underneath the insect and is used to work out precisely where the camera was when each photo was taken.
To turn those photos into a 3D object, the computer uses a subtractive technique similar to carving. It starts by simulating a large volume of space around the insect. Then, for each photo, it finds the outline of the insect. The program makes a virtual ‘cookie cutter’ with the insect’s outline. It puts the cookie cutter where the camera took the photo from, and pushes it through the simulated space. The whole insect must be somewhere in this slice.
With one photo, the cut is just a long prism, and it only looks like an insect from one angle. But the insect is certainly somewhere inside that prism. Analysing another photo creates a second, different insect prism from another angle. The insect was inside both these prisms, so the computer only needs to keep the part that’s inside both. Mathematicians call this the ‘intersection’ of the two objects.
The shape still doesn’t look much like an insect, but by creating prisms from each photo and taking the intersection of all of them, the model gets closer and closer to the actual shape of the insect. Once all the photos are used, the shape is complete. Then the software projects the photos onto the surface of the model, so it’s coloured correctly.
Chuong’s system isn’t perfect – it can’t model surface dips such as an open mouth, or the dimples on a golf ball. But with many shiny and colourful insects including beetles, cicadas, wasps and bees, the system gives realistic results, and looking at one of Chuong’s scans is a lot quicker than driving to Canberra to check out the Australian National Insect Collection!