KAP Aerial Archaeology and Photosynth

I've been frustrated in my attempts to turn KAP aerial archaeology shots into maps, or even into stitched panoramas that bear any real resemblance to reality. For the most part this is because I really don't have the right tools to get the job done. Photogrammetry, and georectification are not simple to do, and most consumer-level tools aren't suited to the job. Typically this involves software like Photomodeler, Leica Photogrammetry Suite, and GIS software. It also typically requires a grid of GPS-referenced ground control points. I'm not positioned to do any of these things.

But I did run across something that produced oddly pleasing results. It's a Microsoft R&D product called Photosynth. It's not so much stitching software (though I use Microsoft's Image Composite Editor for most of my stitching these days). Instead, Photosynth assumes the shots are not taken from the same vantage point, and finds all the points at which the shots overlap. This in turn is used to create a point cloud of intersection points between shots, so a viewer can place themselves at any of the vantage points from which the photos were taken, and see the scene from that point.

All of which is hard to say, but a lot easier to see. I tried this out using one of the flights from last weekend:

It worked remarkably well. Even more fun is to view it with the images turned off so you only see the point cloud of the intersection points between all the shots. Photosynth does a really good job of picking up the three-dimensional structure of the scene.

I tried it with some of my other KAP flights, just on a whim. The archaeology flights were almost all orthogonal to the ground, but most of the time when I'm out doing KAP I'm busy taking oblique shots rather than orthos. I was amazed at how well Photosynth dealt with this:




I think there's a lot of potential for what Photosynth is doing. There are all sorts of other features I'd ask for (and have asked for) beyond the existing Photosynth interface. Among others, it's ideally suited for picking out proper stereo pairs from a whole collection of images. It would be wonderful to have them all gathered, arranged, cropped, and ready to go.

Even better would be 3D model extraction from a random collection of photos of a scene. One KAP flighti n particular resulted in a really good point cloud for a large truck: a deuce-and-a-half. I'd love to be able to export that truck as a 3D model.

I don't know how much time I'll devote to this, but right now it's pretty fun. And for now walking around an archaeological site using my aerial still shots is as close as I can come to what i want: real 3D scene reconstruction.

-- Tom

More Archaeological KAP

I got to do some more archaeological KAP last weekend. The archaeologist I worked with on Ahu A`Umi was on island a few weeks ago, and tried to fly his camera over the lava flows south of the resorts at Anaeho`omalu Bay. It used to be an active quarry for scoria, which in turn was made into abrader tools for working wood, bone, shell, etc. He wanted to see if the quarry and abrader workshops were visible from the air. Foul weather made for a disastrous KAP trip, so I offered to give it a try the next weekend. We traded some email planning out a strategy (wind direction, time of day, angle of light, etc.) and Saturday morning my son and I headed out.

The wind was certainly better than what he'd faced the previous weekend, but it was still turbulent, tossy, and a little too strong. With some reluctance I put up a Flowform 16 and 15' of fuzzy tail, and got down to business. The nature of lava makes it difficult to walk a consistent grid pattern, and I was reluctant to plant my big feet in anything of archaeological value that might be fragile. Nonetheless I spent about an hour and a half pacing around and chanting my mantra: "C'mon baby, steady wind steady wind. C'mon, don't no NOnono... ok, better, c'mon baby..." (I wonder if I'm the only KAPer who talks to his kites.)

At the end of that first session I took my son to a coffee shop at the nearby resort. He had milk and an apple turnover while I sipped coffee and reviewed my shots. As it turns out I'd used the wrong camera settings, and this combined with the turbulent wind resulted in over half the shots being too blurry to use. But there were enough sharp pictures to convince me to give it another try the next day.

The strangest part of the whole experience was that the entire time I was reviewing the pictures I'd taken, the sound system in the coffee shop was playing, Tex Ritter's "I Got Spurs That Jingle Jangle Jingle". I kid you not.

The next day the wind was much more laminar and of more reasonable speed. My son wasn't interested in going this time, so I took my daughter, who brought a book. This isn't unusual for her. What was unusual was that she only brought one. Normally a quick trip somewhere involves at least a small stack of books. "I never know what I want to read when I get there!" pretty much sums up her reason for this. I've quit asking.

The second day went much better than the first. I launched at a second site the archaeologist had marked out, and moved from there back to the original site I'd flown over the previous day. I found a better spot to fly from, and got a better grid the second go 'round. Toward the end of the session the wind was dying down, so I walked the rig back to my launch spot, where my daughter was still reading. I think she looked up maybe once the whole time. So much for getting out to fly kites with your kids. At least she guessed right on her book. It was what she wanted to read.

My daughter had heard of the coffee shop outing with my son the previous day, and was eager to get the same treat. So back we went, my daughter toting her book and me toting a camera with what I hoped were some better pictures than the day before. This time we both wound up getting chocolate croissants, which we munched while she read and I reviewed my pictures. What I saw put a smile on my face. Not only did the steady wind and the correct camera settings work out, the pictures very clearly showed quarry sites, abrader workshops, and even some petroglyphs I hadn't seen from the ground. Euphoria!

But as I continued to flip through the pictures it slowly dawned on me that the coffee shop was still playing, "I Got Spurs That Jingle Jangle Jingle". They didn't miss a beat.

Those two days generated about 3.5GB of data, probably 2GB of which is actually any good. I sent the disks off this morning in the hope they'll be there some time tomorrow. Meanwhile I've got "My Spurs Go Jingle Jangle Jingle" so firmly embedded in my head that even two hours of Linkin Park couldn't clear it out. I've given up. I fear that the very mention of scoria abrader quarries will forever summon up the jaunty notes of "I Got Spurs That Jingle Jangle Jingle":

I got spurs that jingle, jangle, jingle
As I go ridin' merrily along
And they sing, 'Away, too glad, you're single'
And that song ain't so very far from wrong

Oh Tex...

-- Tom