Annnd, this is exactly how humanity figured out astronomy before the telescopes: by taking multi-year observations and keeping detailed records! See Antikythera mechanism, Tycho Brahe, etc. Arguably the entire Greek epistemology was so solid because their astronomy turned out to be an early proving ground for the scientific method.
Combining 15s interval whole-sky-camera photos to form a 4y spanning keogram
31–40 of 93 posts
Re: Combining 15s interval whole-sky-camera photos to form a 4y spanning keogram
#32It took me a bit to understand that it's just the red line from the entire dome. It makes me a bit sad that so much information is discarded for these keograms. Isn't there a way to "peel" the image in such a way that the entire image ends up being the line? Like spiraling or something like that from the outer "rim" to the center point. Nevertheless, it's the first time I've seen this and liked the project a lot. I'v…
The landscape picture there in your link is a different kind of thing; that one has the column used from each individual photo/frame advance from left to right through the day when constructing the final image, so it still looks like the same static view of the landscape. Of course it's also just a different camera view entirely as well.
The fixed column (and upward view) approach used in the main link is better for showing the movement of the sun/moon/stars.
Re: Combining 15s interval whole-sky-camera photos to form a 4y spanning keogram
#33Incredibly cool. I love this so much, both artistically as well as how it demonstrate the equation of time [1] -- the fact that the changes in sunrise and sunset are not symmetrical. On the other hand, it's driving me absolutely crazy that he centers the image at 4:00 rather than midnight. Or maybe that's to show the shimmer of sunlight a little after noon on the right hand side? I can't figure out why it's "bluest"…
One of the commenters noticed this as well, the author says it is something automatic in the exposure. https://fediscience.org/@Birk_lab/113770845539931892
Oh that's a real shame then. The resulting composite images are certainly artistically interesting to look at, and you can see the big-picture effects like sunrise/sunset and moon, but that explains why you can't see the gradual brightening at dawn, or degrees of darkness at night.
It seems like if you wanted to do this accurately, you'd need to lock exposure to handle a bright blue sky without blowing out -- both aperture and shutter speed. And lock white balance. The question is whether that would allow for sufficient sensitivity at night. But if you're just averaging color values across a section of sky and mainly looking for moon and moonlit clouds, I think it would, since pixel noise will get averaged out and the moon is bright.
Re: Combining 15s interval whole-sky-camera photos to form a 4y spanning keogram
#34Annnd, this is exactly how humanity figured out astronomy before the telescopes: by taking multi-year observations and keeping detailed records! See Antikythera mechanism, Tycho Brahe, etc. Arguably the entire Greek epistemology was so solid because their astronomy turned out to be an early proving ground for the scientific method.
This is something I mention to the younger kids at start parties. Way back then, there was no internet, no devices, no tv, no radio, no movies, and more importantly no easily accessible calendars. You couldn't help but look up at the night sky. There was really nothing else to do, and when the only thing available to know when to plant and harvest was based on the constellations visible at the time. It helps put things into a way that helps them think about it even if they can't quite comprehend not having devices.
Re: Combining 15s interval whole-sky-camera photos to form a 4y spanning keogram
#35Earlier quoted context omitted.
One of the commenters noticed this as well, the author says it is something automatic in the exposure. https://fediscience.org/@Birk_lab/113770845539931892
Oh that's a real shame then. The resulting composite images are certainly artistically interesting to look at, and you can see the big-picture effects like sunrise/sunset and moon, but that explains why you can't see the gradual brightening at dawn, or degrees of darkness at night. It seems like if you wanted to do this accurately, you'd need to lock exposure to handle a bright blue sky without blowing out -- both ap…
Yeah, I agree this should be using a fixed exposure (possibly on a schedule) with locked white balance. They are using an astro camera so the sensor is very sensitive, they can get away with extremely low exposure times.
Re: Combining 15s interval whole-sky-camera photos to form a 4y spanning keogram
#36Really cool, this is the first time I've heard of a keogram. I wish there were a corresponding article with a technical write-up covering both the capturing rig and image assembly process. Is there an FFmpeg or imagemagick command, or perhaps a Photoshop script to feed the images into?
The capturing rig itself is pretty simple. It's a straightforward project box you can get from amazon. The camera is an astro camera, but you don't need that- a straightforward USB camera from Arducam would work fine (it has to be a wide angle or accept wide angle lenses. Or a raspberry pi High quality camera.
That plugs into a raspberry pi which runs some sort of script or cron job to take a still image. There are CLI tools to do this as well as modify the camera settings (exposure, white balance, etc). There are some holes drilled in the case with a simple plexi dome. Note inside the dome is a ring of resistors which are given electricty through a relay (which is under software control by the pi) to heat up and keep the enclosure clear. I also see a pressure/humidity sensor (likely used to control the relay) and a fan and some desiccant to help keep it dry.
For the software processing you can use anything; I would write a python script to create a large canvas, and then downscale the images and place them at the appropriate location. You could also load the whole dataset into a large tensor and do anything you want with it.
Re: Combining 15s interval whole-sky-camera photos to form a 4y spanning keogram
#37A site with various allsky cameras: https://www.thomasjacquin.com/allsky-map/
Re: Combining 15s interval whole-sky-camera photos to form a 4y spanning keogram
#38Earlier quoted context omitted.
One of the commenters noticed this as well, the author says it is something automatic in the exposure. https://fediscience.org/@Birk_lab/113770845539931892
Oh that's a real shame then. The resulting composite images are certainly artistically interesting to look at, and you can see the big-picture effects like sunrise/sunset and moon, but that explains why you can't see the gradual brightening at dawn, or degrees of darkness at night. It seems like if you wanted to do this accurately, you'd need to lock exposure to handle a bright blue sky without blowing out -- both ap…
Additionally to locking the exposrue time and aperture, one could also take multiple exposures, figure out the camera's light response function and fuse multiple exposures together into a single higher dynamic range (HDR) image (see OpenCV tutorial on that or Debevec et al. 1997) Assuming you can find the camera response for the very long exposure times at night _and_ the very short during the day, one could relate them to each other and display both for accurate visual comparison.
Re: Combining 15s interval whole-sky-camera photos to form a 4y spanning keogram
#39I generate these type of charts [1] focused on the daylight hours so it was a surprise to see a concave shape instead of a convex one. Awesome way to validate these computer generated charts with captured physical data. [1] https://shademap.app/@52.39941,4.88468,11.49849z,17360064872...
This is really neat. I'm curious where the data for the tree shadows comes from though. I was surprised to see that the trees in my yard and my neighbor's yard were all mapped by your service, since I live in a small town in the middle of nowhere. I read the "how it works" FAQ section, which explained that building shadows come from the map services, but it didn't mention trees.
Re: Combining 15s interval whole-sky-camera photos to form a 4y spanning keogram
#40Wonder if they're going to open source the code they used!