Building a Photogrammetry Turntable

One of our goals with AISOS is to make complicated imaging tasks as easy and repeatable as possible.  We want to be able to rapidly produce high quality products, and we want the process to be accessible to folks with a minimal amount of training.

One of the ways we’ve done that for photogrammetric imaging is by building an automated turntable capture setup.  Conceptually, this is a pretty straightforward solution.  A small turntable rotates an object a fixed number of degrees, then triggers a camera to take a photo.  That process is repeated until the object has made a full 360 degree rotation.  Then the camera can be adjusted to a different angle, and the process can be repeated.

As much as we like doing cool hardware hacking, we also don’t want to suffer from “not built here” syndrome.  We investigated a variety of options for off-the-shelf solutions in this space.  There are a handful of very high end products, which also handle all the camera movement.  These are amazing, but they’re both expensive (nearly $100,000) and, more crucially, massive.  None of those solutions would physically work in our space.

There are also some smaller standalone turntable options that we explored.  However, they’re all essentially small volume homemade products, and rely on proprietary software.  We were concerned about being stuck with an expensive (still thousands of dollars) product of questionable quality.

We then began to look at building our own.  We’re not the first ones to have this idea, and fortunately there are a variety of great build plans out there.  Our favorite was the Spin project from MIT.  Spin is an automated turntable setup designed for photogrammetry with an iPhone. We knew we’d need to modify the setup to work with our camera, but the fundamentals of Spin are excellent.

For our turntable, we completely replicated the physical design of the Spin, using their laser cutter templates and their 3d printed gear.  We used the same stepper motor as well, in order to utilize their mount.  Where we differed was in the electronics.

In this post, we’ll outline the basics of our design and share our Arduino code.  We don’t currently have a full wiring schematic (Sparkfun doesn’t have a fritzing diagram for our chosen stepper driver, and none of us know Eagle – get in touch if you want to help).

Our design is based around a Sparkfun Autodriver. The autodriver is relatively expensive for a stepper driver, but it’s really easy to work with, and is a little more resilient to being abused.  Our implementation is actually based on the “getting started with the autodriver” document published by Sparkfun.  We use an Arduino Redboard as our controller, along with a protoshield for making reliable connections.

The additions we’ve made to the basic Sparkfun diagram include the camera trigger control and the ability to adjust the degrees of rotation per interval.  We’re working with a Canon digital SLR, which can be triggered via a simple contact-closure trigger.  The Canon camera trigger uses three wires – one for focus, one for firing the photo, and a ground.  Connecting either of the first two to ground is all you need to do to trigger an action.  To control that from an Arduino, you just need to use a transistor attached to a digital pin on the Arduino.  Turning on the pin closes the transistor and triggers the camera.

To control the number of degrees per interval, we added a simple rotary selector.  A rotary selector is basically just a bunch of different switches – only one can be on at a time.  We use five of the analog pins on our Arduino (set to operate as digital pins) to read the value of the switch.

 

So far, we’ve been very happy with the build.  We’ve taken many thousands of photos with it, and it hasn’t missed a beat.  We expect that over time, the 3d-printed gear will wear down and need to be replaced.  Beyond that, we expect it to have a lengthy service life.

This is an abbreviated build blog.  We’ll endeavor to provide complete wiring diagrams for any future builds.  For now, just get in touch if you’re interested in learning more about our build.

Creating Exhibits in Omeka

By Nathan Weaver Olson, DCL Graduate Assistant

GETTING AN OMEKA ACCOUNT

The first step in creating an Omeka exhibit is to set up an Omeka account. Currently, the best way for individuals connected with the University of Minnesota to do this is to contact DASH Domains and open an account through them. Check out the DASH website to see if this is an option for you. If you have access to a web server, you can actually download Omeka directly. Alternatively, Omeka will host your collection at Omeka.net. Omeka.net’s basic plan will give you 500 MB of free storage, although more robust storage options are available for an annual fee.

ADDING ITEMS

Once you have Omeka up and running, the first step in building an Omeka exhibit is to add the digital objects or “items” you wish to include in your exhibit to your Omeka account. Do this by clicking “Add an Item”, the green button at the top of the screen. Once you have a new item, you need to add the necessary metadata (i.e. data about the data), which you can do by clicking through the various tabs entitled “Dublin Core” metadata, “Item Type Metadata”, “Files”, “Tags”, and “Map”. For the “Mud-Brick Mosques of Mali” exhibit I added some twenty-three items to our account.

ADDING AN EXHIBIT

Once you have added all of your items to your Omeka account, you can add a new exhibit to your account by clicking on the “Exhibits” tab and then clicking “Add an Exhibit”. The look of an individual exhibit is largely controlled by the exhibit theme. Several themes come pre-loaded in Omeka, but these are just a fraction of the themes available. In fact, users can design themes of their own. In my case, I wanted to use a theme that would allow me to insert my own background image and logo. I settled on the “BigStuff” theme and then added it to our Omeka account using the DASH Domains File Manager.

THEME CONFIGURATION

When you create a new Omeka exhibit, the first page available to you is the “Edit Exhibit” page, where you select and configure the exhibit theme, design the exhibit’s main page, and add new exhibit pages to the site.  In the image below, my theme, “BigStuff”, is clearly visible in the drop down list.

Themes can also be further configured to fit your particular aesthetic and presentation interests. “Big Stuff” allows me to insert my own background image, logo, and header images. In my case, these were images that I designed in Photoshop before uploading them to Omeka.

ADDING PAGES

The content of my exhibit is stored and organized using different pages, accessed through the “Edit Exhibit” link. Each new page includes title and “slug” fields, but users are then able to add one or more blocks of content layouts entitled “File with Text”, “Gallery”, “Text”, “File”, “Geolocation Map”, “Neatline”, and “Neatline Time”.

With the exception of the “Text” layout, all of these page options allow you to pull the “Items” you created into the exhibit. When you add an item, you can also add a caption below the image. I chose to make every caption a link back to the original image in DCL Elevator. My principal goal was to showcase images from John Archer’s collection, but I was also able to locate individual mosques in space as well using Omeka’s “Geolocation Map” layout option.

PAGE ORDER

Finally, when you are on the “Edit Exhibit” page, it is easy to rearrange page order and even nest some pages below others. In my case, I have five principle pages: “Mosque Design Elements”, “Regions and Styles”, “Image Gallery”, Further Reading”, and “About the Photographer”.  Yet several of these pages contain sub-pages, and sub-sub-pages, as a tool for organizing content.

Those are the basics of exhibit building in Omeka. Now that you know the basics, it’s time to get an Omeka account of your own, decide on a narrative you would like to represent as an online exhibit, and get to work adding items to your account.

The exhibit used as an example in this tutorial, “Mali’s Mud-Brick Mosques”, is just one of a number of Omeka exhibits that we have been working to create at the DCL in recent months. We should be rolling them out on our website soon. But you can find Omeka-powered exhibits and websites all over the Internet. Check out Omeka.org’s exhibit showcase for more ideas.

John Archer and Mali’s Mud-Brick Mosques: Exhibit Building with Elevator and Omeka

By Nathan Weaver Olson, DCL Graduate Assistant

Picture a vast interior space, dark and cool, its edges hidden by a forest of columns. The only visible light is that which trickles in through an ornate window screen. You are inside one of Mali’s monumental mosques, a sacred space, and the walls, columns, and even the lofty minaret towers are likely not stone but molded earth, mud bricks plastered with a layer of mud and rice hulls. It is a vulnerable structure in a region of intense heat and seasonal torrential rains, forever dependent upon an army of skilled workers to maintain its elegant and massive form. If cared for, it will last a century or more. If neglected, it will quickly fall to ruin.

In the mid 1990s, Minnesota Professor John Archer, now Professor Emeritus, visited the country of Mali with his camera and an eye for timing and image composition. He took hundreds of images of Mali’s people as well as its natural and built environments. The majority of this wonderful collection is currently housed at LATIS’ Digital Content Lab, where we are slowly adding Archer’s images to the Digital Content Library, which currently contains over 300,000 objects. So far, we have added nearly three hundred and fifty images from John Archer’s trip to Mali to the DCL and organized them into thirty-seven different “works”, each with between one and thirty-nine attached images or “views”. Among the works already available through the DCL is a collection of images of mud-brick mosques ranging from the country’s oldest, to its most iconic and monumental, to more humble examples. It is a unique collection, and now, thanks to Omeka, we have been able to create an online exhibit using many of these images to teach our users about vernacular architectural traditions in Mali while also introducing them to our object database, called DCL-Elevator.

Searching the DCL

One of our goals at the DCL is to make our collections widely available to scholars and students, not only those at the University of Minnesota, but also those working outside of the U. While many items in our collection require the user to possess an X500 to receive access, quite a few of the objects in the DCL are part of our “Open Collections”, objects available to anyone who visits the DCL’s website. Users can currently view Archer’s Mali collection on the DCL by performing an advanced search in Elevator, our database tool, and sorting by collection and keyword.

Elevator includes comprehensive and relatively intuitive finding aids, but here at the DCL we are also looking at additional tools to better familiarize users with the site and its extensive contents. Lately we have begun to do this by building exhibits using Omeka.

Omeka Exhibits

Omeka is an open-source web-publishing platform that is oriented towards users from disciplines within the Humanities. Students, professors, librarians, and archivists can all use Omeka to develop and display scholarly collections. In the case of the DCL, Omeka allows us create exhibits that highlight our collections by focusing the user’s attention on a limited number of objects from the DCL and then sending them into Elevator to find the materials themselves. In practical terms, this has meant festooning our exhibits with links that transport the user to specific images within the DCL Elevator collection. In the exhibit featured in this post, “Mali’s Mud-Brick Mosques”, I put a “Find it in the DCL” link under nearly every image I added to exhibit, as well as a link to an exhibit that Ginny Larson created for the photographer, John Archer.

The structure of an online exhibit, which is essentially a narrative, presents the user with a familiar set of tools for viewing the collection and making sense of its contents. Instead of searching through thousands of images, an online exhibit introduces the user to a finite collection that allows them to approach the more generous holdings of the DCL Elevator database from the vantage point of a specific theme. Because our Omeka exhibits serve to not only showcase the DCL Elevator Collection, but to also extend its pedagogical value for our users, I added a “Further Reading” page to the exhibit as well.

These are all things that anyone reading this post, and especially anyone connected with the University of Minnesota, can do as well. While there are free versions of Omeka available, they have a very limited online storage capacity. But U of M users are able to acquire a more substantial Omeka account through Dash Domains. The DCL has its own domain account through DASH, and through it we have the capacity to access a number of content management applications, including Omeka. To learn more about how to create your own Omeka exhibit, click here for detailed instructions.

“Mali’s Mud-Brick Mosques” is just one of a number of Omeka exhibits that we have been working to create at the DCL in recent months. We should be rolling them out soon. But in the meantime, check out the DCL’s collection and let us know if there are other themes that you would like us to explore as online exhibits.