image : grandfather's knife

fine details & photogrammetry

A simple and obvious trick for catching those fiddly fine details as part of your photogrammetric modelling.

3D models, photogrammetry. All the rage these days. Sometimes though it’s just not possible to model those very fine details you want to record.

There is always the time & data volume tradeoff – it’s not practical to model everything at the microscopic level, or the material is ill suited for photogrammetry, or maybe the available equipment isn’t quite up to standard, or perhaps you just stuff up a shoot.

Whatever the cause some details that are easier (and better) recorded with techniques raking light, hand illustration or RTI.

So why not do both?

You could of course try and model an object entirely in raking light, and again in diffuse light, but that wouldn’t work very well as you loose information in the shadows and highlights that you want from raking light.  But it’s quite simple to take a few extra shots during your modelling that you can use as textures later on.

A tripod (or sturdy setup of chairs and bags of lentils) to hold the camera is essential, but the principal is the same regardless of whether you are using a turntable setup or not.

Every so often in your imaging sequence, take a shot in your main modelling diffuse light, then stop, making sure the camera and object do not move.  Then turn off your lamps (or change camera settings) and use a 3rd light (or better external flash) and take your raking light photographs.  You could even do a full RTI shoot if your setup leaves you enough space to work with.

Then carry on as you were.

When modelling, exclude these images from the process until you get to the texturing stage.  Rename these files to the name of the diffuse images and turn off all other images then build the texture. With care you can texture the whole object in this way, and even trace off fine details and save new images to map onto the model.  You may find UV unwrapping the model and compositing textures externally helpful to get best results.

You can even trace features and save new textures that can be included in the same way.  What’s nice is it creates a very simple record you can revisit that sits well as part of your raw photogrammetry photo archive. And of course you can export each  UV mapped texture for your final model for archiving and sharing too.