Public Lab Research note


What Mobile Apps for Repeat Photography Do You Use?

by chelseak | June 18, 2014 18:43 | 780 views | 4 comments | #10588 | 780 views | 4 comments | #10588 18 Jun 18:43

Read more: publiclab.org/n/10588


Collecting Images of a Location

I'm monitoring a stream restoration project and looking for a quick and easy way to collect images of the changes expected to develop over two years.

I'd ideally like to use a mobile app that helps the photographer line up the image to match a previous shot. It'd be even better if the app helped organize the photographs and let users know when a photo hadn't been taken in a while. Photographers will likely be the landowners and our undergraduate research team.

Have you used an app like this before? What was it? Have you set up a camera stand? What did you find trickiest about it?

Suggestions and advice are most appreciated.

2014-06-02_12.04.10.jpg Turns out dairy cows are really interested in streamflow too.

Information on the Site

A small stream is being fenced off from some grazing dairy cows. The cows like to congregate in the shade of the trees, drink from the stream, and leave behind some phosphorus rich gifts (read: poop). We've noticed they've trampled the banks of this little stream quite a bit and it's likely there is lots of sediment ending up in the stream as well. In addition to the water quality data that we're collecting, we'd like to see how the streambanks change seasonally before and after we put in the fence.

There are several large trees that we could use to frame the image. We've also installed an instrument in the stream to measure flow, which could be used as a reference location. It'd be more ideal to take the picture from the road that crosses the stream just downhill of these pictures.


4 Comments

Hi Chelsea,

I don't have much experience with mobile phone cameras or with mobile phone apps, but I have taken a bunch of repeat photos. An app that overlaid a previous photo on the live view of the camera could help align the new photo with the old (do such apps exist?). But that would get messy if the old photo was not taken with the same camera at the same zoom level. And the camera has to be held very close to where it was when the previous photo was taken. And seeing both juxtaposed images in daylight well enough to align them could be a challenge. Automatic alignment might require a rather sophisticated app.

The hardest part of repeating a photo is putting the camera in the exact same spot where it was when the previous photo was taken, and also matching the focal length. Then you just have to point the camera in the right direction. So if you somehow mark the spot from which the photo was taken, and also place or select a permanent marker in the exact center of the view of the photo, all you have to do is point the camera at that marker. For study plots, a permanent stake can be installed at the center of the scene's view. For landscape views, a landscape element can be put in the center of the view and noted for subsequent repeats. Many cameras or apps have a sighting target at the center of the field which will help place the marker in the exact center of the photo.

Repeating the exact location of the camera can be done with a short stake in the ground marking where to put the same tripod used previously. Or you can install a tall stake that the camera can rest directly on. But installing tall sturdy stakes might be more work than carrying a tripod (or monopod) with you.

If you need really good rectification of the two photos, the most important part is taking both photos from the exact same camera location (using the same camera helps too). If the camera is not aimed in exactly the same direction, the two photos will not overlap completely, but free software is available to align the overlapping parts of the photos, or this can be done manually. This only works if the camera was in the exact same location.

Chris

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Can you use physical hardware in location for people to align their phone or camera to?

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Hi Chelseak,

You can use tinatimelapse or the official app of public lab skycamera: http://publiclab.org/wiki/sky-camera

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It seems putting a stake in the ground for centering the camera would be the best method. like the picture post: http://picturepost.unh.edu/

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