Insight into creating digital 3D models

Not all objects can be scanned using photogrammetry, and there are some parameters for choosing an appropriate purpose.

We selected objects that:

• had a high contrast
• were transportable
• allowed us to view 360-degrees of the object.

Some object don’t lend themselves well to photogrammetry, so we avoided ones that:

• have mirrored, glass or shiny qualities
• are transparent
• are mostly black/dark
• have very thin aspects, such as fine leaves or string
• have crisscrossing objects, such as a tree’s branches
• have very plain and/or featureless textures
• include blinking or moving lights.

For the training exercise, the Education team graciously let us borrow five objects from the Museum’s handling collection. These included:

• mooncake mould used by Chinese immigrants during the gold rushes
• Indigenous carved emu egg
• handmade seaweed basket from Tasmania
• children’s victory medal, given to children at the end of the First World War
• Donald Duck money box from the First Bank of New South Wales.

All these objects have a connection to Defining Moments in Australian History, and all but one item was deemed suitable for photogrammetry learners.

We wanted to test the limits of this technique, so the children’s victory medal was selected as a test case for reflective objects. Typically, it’s tricky to create models of shiny objects as the computer cannot correctly distribute the placement of the images.

We discovered that it takes a long time to mask the object from its background and are continuing to work through this process. The setup of the object and the photography is so important, as it speeds up the process significantly.

Here’s what the team got up to during the workshop.

Setting up

Setting up the objects is an important aspect of photogrammetry. Bad photos create bad renders.

The CDHR team set up two photography systems: one using a light box, and one with studio lighting. Consistent lighting of the object is particularly important as it affects the quality of the final render. If consistent light is not possible, like when using natural light, images can be retouched in post-production, but this adds another step in the process.

Our objects were placed on a turntable. We used either an SRL camera or mobile phones with high-quality cameras. Ideally, the images shouldn’t use zoom or flash to keep them consistent.

Taking the photos

Images need to overlap by at least 60 per cent for the best results. This provides the software with enough information to line up the images correctly.

We placed the objects on a background with high contrast. This allows the software to recognise the difference between the environment and the object so that the environment can be removed later. We then rotated our objects by 10 degrees, or a thumb width, and shot each image.

The objects were photographed from all sides to capture all aspects. The moon cake mould and seaweed basket were slightly more complicated as they had recessed spaces.

Another challenge we faced was getting the children’s victory medal to stand up. We attempted to use a combination of Blu-Tac and bobby pins, but in the end careful placement of the medal’s pin, used to attach it to clothing, was sufficient.

In between each set of images, reference images were shot – usually a funny pose, face or hand of the photographer. This creates visual breaks in the list of photos on the camera that’s helpful when importing them into the system in production.