07 December 2014

Police-related Killings

Like a lot of people, I've been viewing all the recent (and not so recent) news about police-related killings with a mix of sadness and outrage. I was really surprised to find out that the government doesn't collect good data on this and that the number that's often tossed about is just plain wrong.

In the 538 article I just linked to, a few crowd-sourced projects are mentioned:

Then there are some Wikipedia pages on the same topic, with killings listed by month. (Here's November, which is fairly complete.) I've been contributing to the Wikipedia pages and also the Facebook page.

Finally there's the Gun Violence Archive, which is a broader project aimed at providing "accurate information about gun-related violence in the United States."

As I'm watching a lot of communication and cooperation around data projects in my academic life, I'm wondering why these projects can't do the same thing. With at least four separate crowd-sourced projects tracking essentially the same data—though the Facebook page and Wikipedia pages don't include as much detail as the others—that's a lot of duplication of work happening. It would be easy enough to generate most of the entries in the Wikipedia tables from the data in one of the other two projects in the list above, so some of it could be reduced, but there would still be a lot left in those two projects. In addition they've got their data in Google docs, which are handy, but mean a lot of anonymous editing and a reliance on Google to keep the service around (which I realize is more of a long-term worry). FatalEncounters has already had a problem with vandalism and has moved to a much more labor-intensive method for updates.

So I've emailed the responsible parties there and am hoping there can be some deeper cooperation and maybe some better current and long-term access to the data arranged (GitHub?).

I'll keep you posted.

PS In addition to 538, there's also this effort to work with the Facebook data, which also provides a link to those data, which are hard to get from Facebook directly.

04 October 2014

Pole Aerial Photography on an archaeological dig

A recent post by Chiz Howard over at the Urban Archaeology blog covers his efforts to make a pole-mounted camera. I figured I'd share my own experience doing something similar on our site in Italy.

I was mainly interested in getting better quality overhead shots for archival purposes, so what I wanted was a camera view of as close to perpendicular to the ground as I could get, and, ideally, from a fairly high vantage point to include as much ground as possible. It turns out—not surprisingly, in retrospect—that there's a whole community of people out there on the internet who do this sort of thing (PAP, for "pole aerial photography, not to be confused with KAP for "kite"), so I didn't need to re-invent the wheel on this.
PAP in action
PAP in action, with our former apparatus in Paolo's hand in foreground.

My choices were also partly informed by a very practical reality: I had to get this stuff to Italy from the US, since I wanted to test it before going, and I wasn't sure I could get everything once in Italy and I certainly didn't want to have to pay for extra shipping. (Honestly, I hadn't tested far enough in advance to trust the Italian mail to get it to me either.) There is a big Home Depot-type place (Leroy Martin) about 45 minutes away, but I wasn't going to take a chance on them having what I needed.

The Rig

The Camera

Camera equipment
For my camera, I went with a light-weight, inexpensive, but fairly good quality digital camera, the A4000 from Canon (in electric blue), which I picked up for about $100. Canons have the added advantage of being programmable (really "hackable," which is loads of fun in its own right), and of course there's an on-line community for that too. This meant that I could use an existing program (an intervalometer) to have the camera take photos at predetermined intervals all on its own for the whole time it was on the pole. The A4000 is also nice and small, so it's a good camera to travel with. I also picked up a few extra batteries and a charger that shipped with a 12-V car-plug adapter (which I ended up not using). For memory I used 16GB SD cards, which effectively means I never had to worry about running out of storage space. (For the extra-cautious, I find SD cards are also a great way to back up your season files, photos and all, before traveling home.)

Since most pictures were taken in full daylight during the Italian summer, the auto setting on the camera resulted in a low ISO, small f-stop and fairly short shutter speed. For example, in the shot below (as you can see from the embedded EXIF), the ISO was 100, shutter speed 1/1000, and f-stop 3. All of which means I didn't have to worry about the photos being out of focus because of any slight movement in the pole, though the picavet works to dampen those anyway. Just to be sure though, I forced the camera to use ISO 100. The intervalometer program I linked to above also allows you to set a minimum shutter speed and aperture, so you can make sure to get good photos in more marginal lighting conditions. Yet another advantage of the A4000 is a large depth of field, another thing that works to mitigate focus problems.

The Pole

Me setting up with partially collapsed pole
The travel and shipping considerations meant that a lot of the options for poles were out of consideration, unless I wanted to pay for extra shipping or baggage. In the end I went with a 6m (20') collapsible flagpole. Since the camera only weights about 150g (6 ½ oz), I figured that was a lot less than any flag in the wind. It came in a box that was under the "big" baggage limits for the airlines, so I could take it with me without a problem.

The Mount

For attaching the camera to the pole, I decided to go with a picavet, an apparatus that would keep the camera perpendicular to the ground. This requires two attachment points to the pole, and conveniently enough the flagpole shipped with several adjustable mounts. Out of concern for weight I decided to use a cloth picavet.


I ended up being very happy with the results. Not only did we get better overheads than in previous years, from a greater distance and better quality, but they were easier to get, meaning that we took a lot more of them. I was also able to do some photomosaicking with the photos, as I wrote in my last post, which was very nice. (In fact I'm working on a larger-scale one now; food for a future post.) For the future, I'm going to try to make a rigid picavet from plywood or aluminum. The cloth is handy and works, but it gets a bit messy with all the string around. I'd also like to use WIFI SD cards, as I wrote above, so I don't have to keep taking the card in and out.

Overhead of the crew at work. 5m or so wide.

30 July 2014

Photo fun: Using Hugin

Back from my annual month in Italy to lead the excavation at the Vicus Martis Tudertium site and it's time to get cracking on various associated tasks. First up is putting together some of the more adventurous photography work I did, including some pole aerial photography (PAP, as they say, about which I'll do another blog post soon) and 3D work.

For the 3D work, I've been using the for-pay Photoscan application, which works great for me, especially now that I upgraded my laptop to 16GB of RAM. (I'd like to use a freeware option, like VisualSFM, but I can't get it to run yet on my MacBook Pro. I'm working on it now that there's a new installer on GitHub.) The PAP work needs some stitching to create photomosiacs. For that I'm using the freeware Hugin, which is very powerful, but not tremendously well documented, so there's a bit of a learning curve partly due to adapting the old tutorials to the newer versions with their nicer interface.

I already got one photomosaic done during the campaign this summer, just to make sure it was going to work. Here's a small version of the photo. You can catch my feet in more than one place:
It's nothing fancy, just a dry wall, but the technique worked for a ~12m-long stretch, so I've got some more ambitious ones to assemble on. (FYI, the orange things are kids' soccer-field markers that I got to help with aligning the different photos.)

Big inscription from the Roman theater at Ostia Antica.
I'm trying to get up to speed on Hugin's various capabilities in the meanwhile, so I get full use of it. One nice thing it can do is remove various kinds of distortion from photos, including vertical and horizontal effects resulting from your perspective when you take the photo. They call this "Perspective correction". It's fairly simple to do with Hugin and also the kind of thing that's very handy for those of us who take a lot of photos from the ground of big architectural things that therefore end up distorted in the photo. To test it out, I grabbed a photo from Ostia Antica, taken on my last day in Italy this year.

Same inscription corrected.
You can easily see how the nice rectangular inscription shows the expected distortion from being photographed from below. It also has nice straight vertical and horizontal lines, so it's a good object to test the process on.

Following the tutorial, I was able to create a "corrected" version in under half an hour. I used MorphX to create a short video that morphs the original into the final version.

All in all, I'm pretty pleased with the outcome and looking forward to using Hugin with my existing photo collection.

PS In the first version, I incorrectly linked to the "Simulating an architectural projection" tutorial, which is similar, but doesn't include the horizontal correction.