[HN Gopher] Combining 15s interval whole-sky-camera photos to fo...
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Combining 15s interval whole-sky-camera photos to form a 4y
spanning keogram
Author : nebalee
Score : 502 points
Date : 2025-01-04 15:18 UTC (1 days ago)
(HTM) web link (astrodon.social)
(TXT) w3m dump (astrodon.social)
| Tepix wrote:
| https://archive.ph/usfd5
|
| To avoid HN hug of death on this 1832 users Mastodon instance.
|
| Very cool arrangement of those pictures, i was wondering what he
| has done about the daytime pictures when i read the title.
| qwertox wrote:
| It 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've seen this from normal images, but not from
| such a fisheye lens.
|
| Really cool project.
|
| Edit:
|
| Looking at
| https://victoriaweather.ca/keogram.php?photo=20120810.jpg how can
| this contain the entire landscape if only the center line is
| used, which is supposedly always the same line? I mean, the
| camera isn't rotating. Is this just another kind of view
| generated from the dataset?
| jstanley wrote:
| But there are lots of images throughout the day.
| thanatos519 wrote:
| I want a movie made from rotating that red line.
| zerocrates wrote:
| 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.
| gmiller123456 wrote:
| The goal of the keogram is to give a quick overview of sky
| conditions so you can see if there were clouds, aurora, or
| other interesting activity. No information is discarded, as the
| user keeps all of the data, the keogram is just a way of
| identifying which pictures might have something interesting.
|
| The year long keogram presents even less data, as it's just the
| centerline of the keogram for each day. So, essentially just
| the center pixel of each image. Still gives a good overview of
| what the sky conditions were like throughout the year.
| crazygringo wrote:
| Incredibly 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" closest to dawn and dusk.
| I'm guessing the exposure makes a huge difference, and obviously
| the night part is way more exposed than the daylight part, or
| else it would be much darker. Wondering if the camera used
| automatic exposure, and how much of the brightness of colors in
| the image are artifacts because of that? Also if he locked the
| white point hopefully?
|
| [1] https://en.wikipedia.org/wiki/Equation_of_time
| brookst wrote:
| I think the blueness is because clouds at dawn and dusk reflect
| atmospheric colors more, whereas midday the clouds light up as
| more of a white from diffusing sunlight. 100% made up theory on
| my part, but I think it makes sense?
|
| I asked o1 to estimate colors by hour and its reasoning and
| estimates seem fairly convincing[1], and also show more
| saturated blues dawn and dusk, though it did not model clouds.
|
| 1.
| https://chatgpt.com/share/67795fe3-9ac8-8009-9922-153f40c509...
| teamonkey wrote:
| Not sure about the accuracy of the results but the theory's
| correct. The colour of sunlight changes as it passes through
| different thicknesses of the atmosphere and the proportion of
| direct light, refracted light and bounced light changes.
| bee_rider wrote:
| One of the commenters noticed this as well, the author says it
| is something automatic in the exposure.
|
| https://fediscience.org/@Birk_lab/113770845539931892
| crazygringo wrote:
| 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.
| dekhn wrote:
| 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.
| teamonkey wrote:
| > get away with extremely low exposure times
|
| For night sky photography with an astro cam you're still
| looking at exposure times of 20-60s at night (possibly
| also increasing the gain at night) and milliseconds
| during the day. The dynamic range is immense.
|
| As someone who has struggled with this for my own
| allskycam, it's extremly difficult to have white balance
| settings that perform well at all times of the cycle,
| especially with a camera designed to be more sensitive in
| the IR part of the spectrum (which will always look
| unrealistic). Settings that give you lovely white clouds
| and blue skies during the day tend to give you purple
| skies and green clouds at night. The quality of light is
| different so the white balance is different.
|
| You can use autobalance or different white balance
| profiles for day and night but they each have issues.
| jupiterelastica wrote:
| 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.
| sneak wrote:
| #1 rule of timelapse: manual white balance, manual shutter
| speed, manual aperture, manual agc/iso, manual focus.
| fsckboy wrote:
| > _he centers the image at 4:00[pm]_
|
| I think because the night sky offers interesting variation that
| looks nice stitched together. the sunny day, not so much. I
| will also point out, OCD notwithstanding, that 0hour/12am is an
| arbitrary time to start the day, and you should really look at
| the days/nights all strung together in a long continuous strip
| tppiotrowski wrote:
| I 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...
| brookst wrote:
| Pretty! But daylight savings time messes with the aesthetic.
| tppiotrowski wrote:
| True. Argentina doesn't have DST and I just realized living
| in the northern hemisphere made me miss the fact that the
| sunlight hours chart is concave in the south
|
| https://shademap.app/@-50.35203,-70.98027,4.13034z,173600823.
| ..
| brookst wrote:
| Yep. Could flip either one by starting July 1.
| nozzlegear wrote:
| 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.
| isoprophlex wrote:
| I built a similar shadow mapping tool for some commercial
| party that wanted to accurately estimate solar panel
| production in The Netherlands... In my specific case I could
| access very accurate LIDAR heightmaps gathered from planes.
|
| This means you can ray-march the location of the sun
| throughout the year over the entire country to calculate
| exactly where and when a surface is occluded by shadows from
| nearby (or even faraway, sometimes) objects.
|
| The LIDAR data can be as detailed as a shadow cast by
| antennas, a chimney or a tree... Which is more important than
| you'd think, because a little bit of shadow on a single panel
| means that all panels daisy-chained to that panel will see an
| efficiency drop! (So you either don't chain them but give
| each panel its own inverter, or you wreck your neighbors
| chimney)
| tppiotrowski wrote:
| You can train ML to recognize vegetation in satellite photos
| and further train it to estimate its height +/-3 meters
|
| https://github.com/facebookresearch/HighResCanopyHeight
| kbutler wrote:
| I was surprised there wasn't more of a line of red from
| sunrise/sunset.
|
| It's probably because the composition algorithm takes a central
| line through each image (a line through the zenith), so it
| captures relatively few horizon-adjacent pixels that would
| highlight the reds of sunrise/sunset.
| szvsw wrote:
| Highlight related to an analemma: the figure the sun traces if
| you make a parametric plot of its position in the sky at fixed
| time T as a function of the day of the year d, ie f_T(d) =
| (azimuth,elevation).
|
| https://solar-center.stanford.edu/art/analemma.html
| drivers99 wrote:
| I was confused why the night gets so short (looks like 1/6 of the
| time) but I looked it up on a site that shows sunrise and sunset
| times along with twilight and in the summer it doesn't even fully
| get out of twilight. And it seems that there is no
| correspondingly short day because the sun takes precedence in
| that the light can bleed over into the night after sunset /
| before sunrise but not vice versa.
|
| https://www.timeanddate.com/sun/netherlands/amsterdam
| metadat wrote:
| Really 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?
| dekhn wrote:
| 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.
| j7ake wrote:
| Would love to have these figures as big posters as art
| decorations in my house
| fiforpg wrote:
| 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.
| dylan604 wrote:
| 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.
| crazygringo wrote:
| > _There was really nothing else to do_
|
| Well, nothing to do except for storytelling, music, dancing,
| parties, games, plays, sports, eating, drinking, visiting,
| festivals, gossip...
|
| People have been pretty good at keeping themselves
| entertained for a very long time.
| dylan604 wrote:
| And exactly how does that help the specific narrative?
| crazygringo wrote:
| You were writing as if people were staring at the sky all
| night long out of boredom. You said "There was really
| nothing else to do."
|
| That's completely untrue. It's a total misunderstanding
| of what life was like.
|
| I'm not helping your narrative, I'm saying it's a false
| narrative. We have so many misunderstandings about how
| people used to live, it's important not to perpetuate
| them.
| dylan604 wrote:
| Everything you listed as options to do are also available
| now, yet people still choose to stay home and look at
| their devices. Pedantry for pedantry sake is just boring
| crazygringo wrote:
| > _Everything you listed as options to do are also
| available now_
|
| That has no bearing on anything you or I said.
|
| > _Pedantry for pedantry sake is just boring_
|
| Perhaps you don't understand what pedantry is? Your
| entire point was a false description of what humanity was
| like. Just take this as a learning experience! :)
| dylan604 wrote:
| Perhaps you don't know what story telling is. Just
| because details were left out does not mean I'm implying
| they didn't happen. It's not a lie of omission. You're
| hell bent on making something out of nothing, for what
| point I have no idea. But you're free to continue to
| attempt to denigrate my intentions if that really makes
| you feel superior.
|
| You've yet to dispute the actual point that the average
| person did not have a simple device that allowed them to
| see the future without any thought about what it took for
| that to happen. In order to know how much of a season was
| left was to look at the night sky to see what stars where
| visible. Not the day time sky. The only reason they knew
| what they knew because people very intently looked at the
| night sky and started to recognize the patterns. Their
| was no Hey Google! What is today's date? or Hey Siri, how
| many more moons until it's time to plant seeds?
|
| But sure, let's focus on the irrelevant parts of whatever
| story you want me to tell. In fact, how about you go find
| a star party and volunteer your time to talk to kids and
| tell the story however you want. Then come back and we
| can all critique it to ensure you didn't leave out any
| irrelevant details. Maybe we should update the saying
| "those that can't do, teach" to add "those that can't
| teach, critique"
| arduinomancer wrote:
| Obviously OP didn't mean literally nothing else to do
| crazygringo wrote:
| The reason I bothered to respond is that there is a
| common tendency to look back at historical people and see
| them as extremely primitive -- with little knowledge,
| with little entertainment, with little going on. That
| they would have had nothing better to do than to look at
| the sky.
|
| And that's what I'm pushing back on. No, that's just not
| true. Obviously _some_ people were interested in the sky,
| and it was a tool for certain things, but OP literally
| said "There was really nothing else to do." That's a
| complete misunderstanding of human society in history.
| And it's important we don't reduce our ancestors to these
| primitive stereotypes.
|
| It's also important to push back on the idea that there
| were no distractions. OP says "no internet, no devices,
| no tv..." but there was _extensive_ village gossip,
| games, stories... fundamentally we had all the same kind
| of distractions. We 're a lot more similar than OP
| thinks.
| dylan604 wrote:
| You're now assuming that I'm a bumbling idiot that thinks
| everyone before electricity were neanderthal cavemen.
| Although, I've met plenty of modern people that couldn't
| hold a flame to a caveman.
|
| The fact that the ancients knew the coming of the seasons
| and developed their entire society based on what was
| visible in the heavens just shows how much they _did_ pay
| attention to it.
|
| There's a thing in story telling called hyperbole. It
| helps enhance the story by bending the truth just a bit
| to make the story more interesting and helps get a point
| across. It is especially useful in oral story telling.
|
| But clearly, we're all bumbling idiots for not getting
| the minute details exactly right. Good to know. I'm glad
| you're so intelligent that you've set me straight
| globular-toast wrote:
| I guess he meant there was nothing else for nerds to do...
| morsch wrote:
| Like the sibling, I don't think people had trouble
| entertaining and distracting themselves. But there was no
| electrical light, and much less artificial lighting overall.
| Evenings and nights were dark. I'm sure many a walk home
| after a gathering was lit only by the night sky.
|
| Meanwhile, I can see the moon and like ten stars on a typical
| night, because I live in a city and there is massive ambient
| light at night.
| dylan604 wrote:
| I initially had something referencing light pollution, but
| felt it wasn't as relevant to the point and took it out.
| When talking to kids, giving them the whole nine yards at
| every opportunity is overwhelming. Giving them just enough
| to get the point across is much more effective. Explain
| once without over explaining, demonstrate, and then let
| them experience it. Never been a teacher, but it works as a
| coaching technique that translates well in other areas.
| Giving too much info that's not relevant verges on
| mansplaining IMO.
| gsich wrote:
| A site with various allsky cameras:
| https://www.thomasjacquin.com/allsky-map/
| elintknower wrote:
| Wonder if they're going to open source the code they used!
| diyseguy wrote:
| Why does the sun shrink and disappear just past the halfway point
| on the keogram?
| icehawk wrote:
| This post? https://astrodon.social/@cgbassa/113770444896606353
|
| That's the moon, and it looks like it's increasing cloud cover
| + dawn causing camera to decrease overall exposure.
| isoprophlex wrote:
| This is fantastic, and like another commenter mentions, a
| beautiful continuation of an age old practice: measuring the sky.
|
| Very cool that their hardware keept chugging along for years
| without hiccup, too.
|
| If you want to do something kinda similar but far less involved:
| a very lo-fi, no computer involved thing to do is an ultralong
| photographic exposure (months, a year, longer) with a pinhole
| camera.
|
| The results are quite artistic IMO [1], the camera is fire-and-
| forget and you don't need any chemicals to develop the image.
| Just photograph/scan the photographic paper and invert the
| colors.
|
| I'm not affiliated with them, but Solarcan sells ready made
| single-use pinhole cameras. An almost zero-regret purchase I'd
| say.
|
| [1] You see the sun move through one year of skies, as seen from
| my balcony: https://files.rombouts.email/IMG_6500.jpeg
|
| People have made wonderful, mildly spooky pictures with these:
| https://solarcan.co.uk/wp-content/uploads/2018/05/solarcan-p...
| arduinomancer wrote:
| Wow that is a cool concept
|
| Thanks for sharing
| leobg wrote:
| https://solarcan.co.uk/
| bikamonki wrote:
| So cool that the shape resembles an hourglass!
| mjbrownie wrote:
| I work with a shorebird expert who has been tracking migrations
| (Latham snipe whose range extends from Russia/Northern Japan to
| Southern Australia).
|
| I think an early technique of tracking their migration before
| gps/chip/batteries were small enough was a primitive light
| sensor + data logger that would log day/night hours on the bird
| as it flew from island to island and the light data was enough
| to roughly estimate lattitute (and often enough to infer a
| location/date.
|
| The data looked great in this form. It wasn't hourglass but
| with jagged edges and shifts. You could easily see which months
| the bird stayed in a single place for several days etc. clever
| stuff.
| gmiller123456 wrote:
| You've got much better weather than we do. Here's mine from near
| Louisville KY (from Aug 2023 to Aug 2024)
| https://www.facebook.com/groups/101640086556073/posts/794426...
| russellbeattie wrote:
| It's easy to forget how far north Europe is! The daytime vs
| nighttime hours is so much more extreme there. The Netherlands
| is on the same latitude as Newfoundland in Canada.
|
| I noticed the extreme hour glass shape in his image, but it's
| even more impressive when compared to yours!
| incognito124 wrote:
| I always forget how south the US is. Rome is approximately at
| a similar latitude like Boston!
| th0ma5 wrote:
| This Python conference presentation from over a decade ago
| includes an adjustment of such a visualization for DST which I
| think of often
| https://www.slideshare.net/slideshow/observational-science-w...
| th0ma5 wrote:
| This site also has that view for a lot of places
| https://www.timeanddate.com/sun/usa/columbus
| hinkley wrote:
| My favorite work in this vein is still the guy who did the
| trigonometry to convert a year+ worth of telemetry from a light
| level sensor in his back yard to paint a picture of the tree
| canopy. Each day is a scan line of light and dark patches at a
| different solar inclination. So everything above the sensor
| eventually got "painted".
| azepoi wrote:
| Have you got a link or do you remember the name of this person?
| hinkley wrote:
| Oh gosh it's been a while. I thought it might have been in
| r/dataisbeautiful but I'm coming up with nothing. I have a
| vague recollection of what the picture looked like but search
| isn't turning it up.
| acegopher wrote:
| I did much the same thing (and much more) 10 years ago. I used a
| RPi as well as a Canon point-and-shot out my window. My pics were
| 1 per minute.
|
| Here is a link to the keogram section (I didn't know the term),
| but watch the whole video, I did a bunch of other art:
|
| https://youtu.be/Mfo4hVc71Qw?si=3YKojggkTj2xehAB&t=2334
| kaeland wrote:
| I really enjoyed your faces example! I'll have to look at the
| rest of the video soon, but it's so cool what you can do with a
| little imagination and ingenuity!
| imoreno wrote:
| This is neat, but the amount of data seems overkill just to see
| the trend in day/night length and the keogram is a bit busy. It
| seems like compressing each day to 1 px tall would result in a
| clearer representation of that.
|
| It's neat that you can look at different things, like cloud
| cover, the moon, stars and anomalies (such as the aurora). But
| these are convoluted in the raw data. Deconvoluting these to
| obtain a keogram of just the sun, just the moon, just the
| anomalies would probably make for some interesting
| visualizations.
| gregfjohnson wrote:
| This brings to mind something I've wondered about for a while.
| Sunrise on the shortest day of the year is earlier than sunrise
| for several days after it.
|
| Sunset on these days after the shortest day is of course even
| later than sunset of the shortest day.
|
| On the beautiful image of the OP, you can see that after dawn of
| December 21, dawn continues to get later over the next few days.
|
| In my area, sunrise on 12/21/2024 was 6:54am, and it will
| continue to get later until 1/8/2025, when it is at 6:59am.
|
| Length of day on 12/21/2024 is 9 hours, 54 minutes, and length of
| day on 1/8/2025 is 10 hours, 2 minutes.
|
| Searching the web, I haven't found an explanation for this that
| "clicks" for me as both intuitive and rigorous. Any thoughts or
| pointers on this?
| raimondious wrote:
| I don't know if this is sufficient but there was just a
| StarDate about the topic https://stardate.org/podcast/2024-12-3
| incognito124 wrote:
| The apparent movement of the sun is not influenced solely by
| the Earth's rotation, but also the instantenuous velocity of
| revolution and also the fact that Earth's axis is slanted
| w.r.t. the ecliptic.
|
| Study this Wiki article, especially the components part:
| https://en.wikipedia.org/wiki/Equation_of_time
| KineticLensman wrote:
| It's partly because we have a standardised 24 hour clock and
| solar noon (when the sun is highest) is sometimes ahead and
| sometimes behind GMT noon. The sunrise and sunset times relate
| to solar noon so they vary accordingly.
|
| See 'equation of time' and 'analemma' for underlying
| astronomical explanations, as hinted at by sibling posts.
| gregfjohnson wrote:
| Thanks, very much appreciate the thoughts and pointers!
| xeckr wrote:
| The dress, anyone?
| rollulus wrote:
| Could someone explain to me why the sun-rise/set doesn't seem as
| sinusoidal as I would naively expect?
| justinl33 wrote:
| the real technical achievement here is maintaining consistent
| camera sensitivity over 4 years. Most consumer CMOS sensors
| degrade significantly from UV exposure over that timeframe, which
| would show up as a gradual darkening in the composite
| krm01 wrote:
| Wow this is really beautiful. Is there an algorithm (not api, but
| available calc method) that can calculate the full year based on
| a few variables? Like long+lat?
| leobg wrote:
| The "stripes" in the keogram look very regular. A few days of
| clear skies followed by a few days of clouds. Is that what's
| happening? Why the regularity?
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(page generated 2025-01-05 23:01 UTC)