First, update timing controlled by the browser, not the server. IF you look at the source, you'll see near the top this line:
<META HTTP-EQUIV="refresh" CONTENT="60">
This is what Riley was describing as one of the two possible approaches; it tells your browser to re-request the page in 60 seconds. If there is some variation in updates, that derives from one of several possibilities: (a) your browser doesn't time the refresh exactly; (b) connection delays slow down the update; (c) the specified refresh time is not always 60 seconds.
Second, what gets refreshed is the entire page, not just the image. Since there is not much to the page besides the image, this may not be visually apparent just from watching the update process.
Third, the image name changes every minute (or, more exactly, every time the image changes). You noted this yourself.
How they update the source is not apparent from what we can see ... but that part does not matter to your problem.
So ... were I to automate this process, I would probably do it by way of a Perl program that did the following:
1. Use wget (or the appropriate Perl library) to download the page, using its URL, to a scratch file.
2. Parse the page text to extract the image name (which I assume will always have the form sun*.jpg).
3. Use wget (or the appropriate Perl library) to download the image file to a scratch location.
4. Use some suitable program to display the image on the X display.
Either run this program through crond, every minute, or run it in the background continuously, with its own internal timer (a crude one using sleep, or a more active one checking the clock ragularly, or a mix of the 2).
The problem with all of this, Haines, is merely what I said before ... there is no standard way to do this sort of browser updating. So for any site you want to tap into this way, you need to look at the specifics of how the site does the updates (or, I suppose, write an update client that has the full capabilities of a browser, but this approach seems a bit too ambitious to me).
BTW, were I interested in this, I would just look for 2 more sites that do something similar, in different parts of the world, and extend the Perl program to switch among them based on the time of day ... at least this deals with sunrise/sunset limitations, though not stormy weather.
At 11:17 AM 5/31/2003 -0400, Haines Brown wrote:
Ray,
An interesting puzzle, although perhaps a bit academic. The image I'm talking about are those put out by the National Solar Observatory at Sacramento Peak, I realized after raising the question that, not only is the sun not seen when it's cloudy, but not at night. So as a background image, it would be too often not available.
The URL for the perversely curious is: http://solar.spacew.com/sunnow/
But I could imagine that a resolution of the problem would have some interesting uses. For example, a video camera aimed at Times Square or goldfish would produce diversions. The reason for the sun image was that it displayed extraordinarily powerful solar flairs, the effects of which just reached earth yesterday and today. For many people, that's important to know.
> OK. But having said that, what does Haines actually do? > > If, for example, the image being fetched always has the same name > and is fetched by its name (something_or-other.jpg, for example, > rather than something_or_other.asp or something_or_other.cgi), then > Haines could probably imitate the functionality he sees faqirly > easily,
The images are numbered in sequence. For example, Sun269169.jpg, Sun269170.jpg...
> But the actual call may be to a changing image name (if it uses the > Javascript approach, or perhaps a Java applet, it might incorporate > a timecode, say), or it may require a cookie, or it may be a cgi or > asp call that requires get or post options. Any of this would be > harder to emulate ... and that's why I say the devil is in the > details.
The web page offers no clue how the images are generated. Just an <img src=sun369177.jpg... tag for example.
> Anyway ... my sense is that this problem is best split into two > parts.
> Haines, in his second message, calls the image "constantly > changing", and that ("constantly") can't be right.
True. I mispoke. It updates every minute, but since the site worries about whether the updating occurs, it seems to have an internal timer. I don't get the impression that the images are uploaded exactly every minute on the minute, but rather somewhat haphazardly.
Haines
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