Thanks to a Make|Learn|Build! grant from the Oregon Regional Arts and Culture Council (RACC), I have been able to spend time working with some current 3D imaging and CAD software to see where and how these technologies might be suited in a custom shoe making workflow.
Part of the money I received was used to purchase a Structure Sensor Pro. This scanner is based on infrared light, similar to the Kinect and other structured light scanners. Structure Sensor Pro requires an iOS device to run, so I also had to buy an iPad. With this handheld scanning setup, I acquired scans of 5 pairs of feet. I also scanned some of the lasts used for this project and lasts used to make shoes previously.
Scans of feet must be manipulated in some way to make them fit into the digital last models. Most feet are scanned on a flat surface, but most lasts are not flat. A lift of the heel is needed and some lifting of the toes as well. This already requires some assumptions about how a foot might behave when manipulated in this way. Even though I could manipulate the scan of the foot enough to make it fit inside the bounds of the last, the scan data does not provide enough information to know if this is actually possible for the given foot, or if it would be a comfortable and pleasant fit.
My original plan was to use a customized CAD program offered by the German last manufacturer Spenle. They offer this on their website, but I could not get them to sell or license a copy to me or work with me in any way on it. I purchased a copy of Rhinoceros 7, a very capable CAD program that is also well represented in the footwear world. This also meant I had to learn CAD for real in order to make a usable model of a last to send out for production.
I wanted to adjust digital models of lasts based on scans of feet for each person scanned and then have those carved to see if I could begin the custom shoe fitting process from a better starting point than if I just ordered by length and width. I did indeed do this, but only for one individual. Because I did not have access to the library of lasts from the last manufacturers, I had to buy scans of lasts and build my own models. I modified the physical lasts to fit and then compared the scan of the modified last with the scan of the feet to visualize feet in a last that fits. I also very significantly modified a model and sent it out for carving.
Shoes and Fit
For each person trial shoes, or fitting shoes, were made and the lasts adjusted as needed before the final shoes were made. The real test of whether the last fits is whether the shoe fits. Since I have some experience fitting feet, lasts and shoes, I thought it would be interesting to see how this fit is visualized.
In practical terms scanning feet using a handheld scanner is pretty fussy. It can take quite some time and the results vary in accuracy. It is difficult to capture the feet from every perspective in order to obtain a complete 3D scan. I used the same scanner to scan lasts, but the edge detection is not good enough to get clearly defined edges especially around the feather line.
The visualization of the feet and lasts is not intuitive. While I think most people would imagine that a foot fits inside a shoe, and thus a last, and in seeing these two things together, one might expect to see just that – a foot inside a shoe. In real life, the foot really does go in the shoe. On the computer the foot protrudes in all sorts of way that would lead an untrained observer to assume a particular combination of foot and last is not a fitting one when in fact it is.
Consider the “hand in glove.” A hand goes in a glove and if you scan a hand and a glove, it’s extremely unlikely that these two shapes will line up on screen as well as they fit in the physical world. This is a limitation of computer modeling of elastic forms. The real world is elastic in ways that the computer is not. This is not to say that the computer can’t model elasticity at all, only that the wild variation of mobility and flexibility in human beings can’t be captured by a surface scan and modeled using only that. It’s important to set realistic expectations and know the limitations of the medium.
Below are images of feet and lasts and the shoes made on those lasts. Can you tell which of these fit to the satisfaction of the wearer?
These images are of works in progress. The fitting shoes have been made and the results are good, but the final shoes have not yet been made.
Many Kinds of Fit
To state the obvious, the size alone does not determine the fit. The fit really depends on the shoe. Not just the shape of the shoe, but what the shoe is made of and how it is put together. Shoes of the same size but different materials and/or different construction techniques will not fit the same. One person may also have many fit preferences. Maybe sometimes they want a loose fit and other times a tight fit. Most people prefer a range of fits. Shoes are made for many types of uses and occasions – ritual and otherwise. For some occasions the fit is as socially constructed as the look. None of this is readily visible even in a really good 3D scan of a person’s foot.
Visualizing the Fit
With the examples I’ve provided here, it is possible to see how the digital images of feet and lasts can be combined to visualize the fit. With some insight and knowledge of anatomy and biomechanics, feet and shoes, it’s possible to make sense of these images and discern the ways in which a particular fit might be displayed. The difference between a shoe that fits really well and one not that great can be very small, and possibly not even something one could see in the images.
Facial recognition software can do a decent job of identifying landmarks of a face, but it can’t tell you anything about the personality behind the face. Likewise, 3D images of feet on their own are not enough. In many ways the blueprint, or Harris Mat print, provide more useful information than a surface scan of a foot. To get a complete picture, you have to know more about the feet, and shoe that was or will be made and more importantly, the person who will wear it.
In the process of gathering all of the information needed to successfully make custom shoes, 3D imaging of feet can play a part. The bigger role for 3D imaging, in my opinion, is the ability to capture and reproduce lasts that have been modified to a wearer’s preference. To make adjustments to digital last models and to be able to compare these changes is valuable indeed. For capturing images of feet, infrared scanners might be serviceable enough, but a more accurate scanner is needed for lasts.