Wikipedia:Reference desk/Archives/Computing/2012 September 5

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September 5

Bluetooth

If two identical cell phones were fixed in place mechanically so that, to the submicron level, the relevant components were the same distance from a bluetooth headset, and the headset were then turned on, how would one cell phone acquire the headset over the other? Peter Michner (talk) 12:46, 5 September 2012 (UTC)

Every bluetooth-capable device has a unique identification number (BD_ADDR). Using this they can unambigiously identify one another by this means alone. BD_ADDR is used during pairing and authentication so you know which headset you're connecting to, and so no-one can spoof that headset and impersonate it. If both of the headsets in your example have already been previously paired with the phone (meaning it's stored their details) and they're both turned on simultaneously, it's up to the phone to decide which it prefers. -- Finlay McWalterჷTalk 13:42, 5 September 2012 (UTC)

Sorry if I wrote it wrong, but I was saying if you have two phones and one bluetooth thing to which neither phone has ever been linked, how would one of the two phones get connected with the one bluetooth earpiece. I know with my Jabra bluetooth earpiece, the first time I ever turned it on in close proximity to my iPhone, my iPhone immediately showed the little bluetooth icon in the upper right corner, meaning my iPhone linked with the Jabra earpiece. What if two cellular phones were precisely the same distance from one bluetooth device that has never connected to either and the bluetooth device was turned on? Peter Michner (talk) 13:55, 5 September 2012 (UTC)

Bluetooth has a sophisticated protocol, because it is a fairly modern form of digital communication. This is a special case of the more general problem of resolving collisions in a shared transmission medium. Each type of wired or wireless technology has a mechanism for handling this case; some similar methods are carrier sense multiple access with software-controlled re-tries that are timed randomly to avoid repeating the collision. Other schemes use address-based coding, so that the message is only decipherable to its intended recipient. In some communicaton systems, like aviation radio, voice procedure is used to handle collisions (at the "Application Level" of the OSI stack): you simply say who you want to talk to, and if the message gets garbled, you try again. For a very specific answer to your question, we'd need to dive into the details of the Bluetooth protocol specification. Often times, the solution is a mechanism designed to guarantee a strict ordering among devices, even if the individual devices are unaware of others on the shared radio channel. Nimur (talk) 13:59, 5 September 2012 (UTC)

Hard Disk Docking Station vs 'Portable' HDD

I am considering the puchase of an external hard disk drive (HDD) for storage/backup purposes for a laptop with a 500 GB internal HDD. (I am recording TV from a digital USB TV 'stick' and it takes a lot of space, about 5+ GB an hour!)
One possibility is a 'portable', USB powered HDD of about 1.0-1.5 TB. Another possibility is a USB interface HDD docking station, the type that takes 'bare' (uncased) HDDs, as I have a spare 3.5" 1 TB HDD available.
Any knowledge, experience, reviews etc. of the merits of such a docking device vs a more portable 'cased' type HDD? Regards, 220 of ^Borg 17:43, 5 September 2012 (UTC)

The cased HDDs are usually nothing more than a docking device plus a normal consumer HDD, although the cased HDD may actually be cheaper than a docking device plus HDD, because they're produced in much greater volume. A merit of a cased model might be simplicity - it saves you the trouble of putting one together yourself, and (especially the 2.5" models) may be able to work off the power provided by a USB port, saving you the trouble of carrying both the drive and a power supply. Unilynx (talk) 18:21, 5 September 2012 (UTC)

Unilynx, Concur that "cased HDD may actually be cheaper than a docking device plus HDD". It certainly seems to be true. However, next week(12/Sept.) my local ALDI store will have a USB 3.0 dual "HDD Docking Station" for SATA drives going for A$30. I actually have a lot of 'miscellaneous' HDD lying about, so it may be useful for purposes (ie. HDD testing) beyond backups. - 220 of ^Borg 18:22, 6 September 2012 (UTC)

Typically docking stations do not offer any protection to the hard drive and are not intended for constant use. The hard drive will be more susceptible to damage and dust as it is exposed rather than being shielded in a case, and the interface connectors (especially IDE) are not designed to be regularly attached/detached and may break. A disk enclosure may be more suitable. Worth noting; some external hard drives such as the FreeAgent GoFlex have a detachable base so can function as both a cased hard drive and as rudimentary docking station for other SATA hard drives. I would not recommend this for constant use however, but if you only needed to access the spare 3.5 drive very occasionally it may be useful. You might also consider encoding your video into a more efficient codec such as h.264. Recordings from DVB will probably be mpeg2, so the space savings in using h.264 can be considerable as it will produce similar quality at lower bitrates. AvrillirvA (talk) 19:26, 5 September 2012 (UTC)

Actually in plenty of countries DVB transmissions are in h264, the OP didn't seem to specify where they live either in the question or in their user page. Also despite the OPs choice of words, I suspect they're referring to standalone portable hard disk enclosures which still exist. However IMO such devices often no longer make sense. In a number of countries 3.5" based portable hard disks, when on special at retail stores are often cheaper then internal ones. And ironically with the terrible internal HD warranties nowadays the portable ones often have longer warranties. Anyway I have to question whether the OP has considered their requirements properly. If they only need portable within a house I would suggest they should set up a dedicated media server and use their laptop as a client. They could also use their laptop with an NAS but I don't see why you'd want to record stuff on the laptop unless you plan to take it around and still be able to record while on the move. If they want to content to be available, perhaps provide some local caching of important content? Nil Einne (talk) 06:52, 6 September 2012 (UTC)

@ AvrillirvA, I have one of those enclosures ... somewhere! though actually more of a slide in/out tray type for a tower PC. I have been considering the FreeAgent GoFlex as a possibility, but they seem rather more expensive per Gb. I can get the GoFlex 'dock' for 'only' ≈A$25. See also my rpy to Unilynx re "HDD Docking Station".
• I don't think I have any choice about the encoding of my saved video. It is MPEG (.mpg file extension). According to the specs it is MPEG 2. One recorded movie from GO! has a video 'Data rate' of 3135kbps,' total bit rate' of 3391 kbps, Audio bit rate of 256 kbps, if that gives you any more clues about the encoding used. The software is ArcSoft TotalMedia, bundled with a MyGica brand MY-T803 DVB-T TV stick.- 220 of ^Borg 18:22, 6 September 2012 (UTC)

@ Nil Einne, I am in Australia(Oz), southern end of Sydney. I would like the HDD to be pretty portable, rather than a 'Desktop' type, so a USB powered 2.5" external is what I had in mind, though noticeably more expensive. Currently JB Hi-Fi have Seagate/ Western Digital 1Tb for A$99. Very tempting, or Dick Smith has Seagate 1.5 TB available for $149. A 'desktop' 3.5" not intended to be carried around is about 2 Tb for $A135.
A media server is certainly a possibility, one which I had not considered. I have plenty of unused computer hardware lying around to build one (or even 2!). (Perhaps you can also advise me why I can get 'Gem' digital TV video, but no sound! I also cannot receive 7mate or similar channel 7 stations, and GO! channel reception can be very spotty, though sometimes it is perfect!) Oh NZ I see, thought you were in 'OZ' ;-) - 220 of ^Borg 18:22, 6 September 2012 (UTC)

Suggestion for reader-controlled highlighting in Wikipedia articles

Dear Wikipedia,

As I don't know where to put my this question, however I arrived here.

Since I read wikipedia most of the times, and wikipedia pages are open for many hours a day. So when I change my tabs, I loose my sight from important lines in previous tab. So I want you guys to add some facility, so that I can highlight my important lines with some colors. ( Here I want to tell you that in a wikipedia page, you can highlight ONLY one continuous line with blue ink (as it happens in all the pages, if it is wikipedia or any other ), what if I want to highlight many lines on the SAME page.)

Please add this facility to Wikipedia, so that everyone can take advantage of it.

All for One and One for All.

Thanks. — Preceding unsigned comment added by 180.149.62.52 (talk) 17:45, 5 September 2012 (UTC)

The place to make suggestions like this is WP:VPT. Making them here won't lead anywhere even if people like them. Looie496 (talk) 17:48, 5 September 2012 (UTC) (PS, I have removed your email address, as it makes you a target for possible spam.)

Here we answer questions relating to computers. For instance, if you wanted to know how to make multiple discontinuous selections on the same page in Firefox, the answer [1] is that you hold down the ctrl key.  Card Zero  (talk) 18:46, 5 September 2012 (UTC)

You might also be interested in the Awesome Highlighter, which will allow you to highlight text on many sites, not just Wikipedia. There's a Firefox extension as well as a browser-independent web-based version. - Cucumber Mike (talk) 21:38, 5 September 2012 (UTC)

What's the point of LaTex?

It's nerdy, complicated, ugly (apparently like the people who love it). And on the top of that, when you submit an article to a magazine, they want a rtf or Word file. Comploose (talk) 18:00, 5 September 2012 (UTC)

It's important to realize that LaTeX was created in the early 1980s, and TeX even earlier. If somebody was starting from scratch nowadays, they wouldn't create a system that works that way. Even so, it still has some nice features for some people: (1) it is excellent for complex mathematical formatting; (2) it still produces very nice looking output in comparison to Word. Looie496 (talk) 18:05, 5 September 2012 (UTC)

It was created at a time when printers were capable of displaying fancy typography but computer displays could not display anything fancy. Think monochrome monitor and IBM 3270. Since then, various ways of WYSIWYG have become possible, but they are proprietary and incompatible. So LaTex remains as a platform-independent way to produce fancy typography. Jc3s5h (talk) 18:08, 5 September 2012 (UTC)

Compared to word and similar products, LaTeX has: 1. superior looking output; 2. smaller file sizes of documents; 3. needs only a text editor to write, i.e. no need to install programs (of course creating pretty output will require installation of LaTeX); 4. encourages the writer to focus on content and the logical structure of the document instead of on the formatting, 5. free of charge; 6. wide variety of packages (from Klingon to typesetting chess boards); 7. in my experience more robust particularly if you use labels/references/citations; 8. potentially quicker for experienced users to write documents (might depend on type of documents)

As for complicated, I find it easier to use than word (which I only use irregularly). Some magazines actually encourage the use of LaTeX submissions. bamse (talk) 20:03, 5 September 2012 (UTC)

Bamse gave a pretty good list, but left off a couple of the points that are most important to me:

1. The "source code" is human-readable, not a binary file.
2. The format is open and stable; it won't go away because some company decides to stop supporting some version of an application (this point may have been somewhat addressed by the XML-based versions of Office; I haven't really looked into that).
3. If you want to use the same content in a completely different style of document, it's often as simple as changing a single line in the preamble. You don't have to figure out what exactly you have highlighted, whether it's content or formatting, and worry about the vagaries of "smart paste".

The principal downside is the heavy learning burden. That's a legitimate objection. If you don't want to shoulder that burden, just say so. Don't insult the people who are willing to do it. --Trovatore (talk) 20:21, 5 September 2012 (UTC)

I would throw in an additional downside, which is the immense diversity of different implementations of TeX and LaTeX from site to site. There does not seem to be, in actual fact, a "standard" form of TeX; both its toolchain and its format and layout packages vary hugely from place to place, user to user. For this reason, I find claims of simplicity dubious. As an example, ask a friend or colleague from another university to please send you their last-published paper's TeX source; and attempt to compile it on your system, without modification. It's clear to me that semantic markup has great merit, but I find the TeX ecosystem to be lacking, compared to competitors. Even HTML provides a more standardized mechanism to separate form and content. LaTeX users will quickly attack HTML because it "cannot" nicely render mathematical equations; but this is counterindicated by numerous examples. And, it is my contention that if you're actually concerned with separating presentation and content, you should not be so worried about whether your integral sign renders at full height. Thanks to the engineered precision of the Unicode standard, there are a wide array of representable mathematical symbols: "∭∮∀" and literally thousands of other mathematical symbols and operators ... which are all semantically distinct, and easily representable or renderable with the appropriate choice of font, glyph, and layout. All of those layout issues can be resolved using, for example, CSS - cleanly separating content from presentation, in a standardized format, free of any proprietary technology, and most importantly, easily readable on every modern computer platform in common use today. Nimur (talk) 20:36, 5 September 2012 (UTC)

It's not clear to me what you mean that you shouldn't be worried about how your integral sign looks. To address one possible interpretation of your words, of course separating content from presentation doesn't mean you don't care about presentation. It just means that you want the program to take care of presentation automatically based on the logical structure of the content, and you want it to automatically look nice. Does HTML ever do that? I haven't seen it, at least without extensions such as MathJax. LaTeX mostly does a pretty good job of it (the main exception is the somewhat awkward treatment of floats; if you really don't want them to float, which I often don't, it can be a pain to get them where you want them).

As to the proliferation issue, yes, it can be a problem if you try to skimp on what you install, but when I install full tetex or TexLive I haven't observed it being too much of an issue. At most you might have to google around for a .sty or .cls file or two, at least providing the other person isn't using some mutant version like PCTex.

To me the Unicode symbols really don't look as nice, at least on any rendering system I've ever seen. Also the relationship between two similar Unicodes is harder to discern than it is with TeX defines. --Trovatore (talk) 21:48, 5 September 2012 (UTC)

TeXworks automatically downloads and installs 'whatever' on the fly when you try to compile a document that has \usepackage{whatever} that is not on your system. 67.163.109.173 (talk) 22:06, 5 September 2012 (UTC)

I forgot one:

4. If you work on a TeX or LaTeX document in a revision control system such as CVS, the diffs are meaningful — you can see exactly what was changed between two revisions, not just that it was changed. --Trovatore (talk) 22:19, 5 September 2012 (UTC)

Also, it's easy to generate or modify (La)TeX source programmatically. --Stephan Schulz (talk) 23:14, 5 September 2012 (UTC)

WK seems to use both html and LaTex: Wikipedia:Manual_of_Style/Mathematics#Typesetting_of_mathematical_formulae. OsmanRF34 (talk) 23:32, 5 September 2012 (UTC)

See here for the reason it was created. Zoonoses (talk) 04:18, 6 September 2012 (UTC)

JPG not working in a WIki

I've been uploading some files to another Wiki. Most of them are OK, but some completely fail to show up, producing a blank screen. They all look OK viewed on my PC at home, and there's no obvious difference between those that work and thoses that don't. You can see one of the images at http://www.foxearth.net/Halfway_to_Heaven.JPG. Any suggestions as to what the problem could be and how to overcome it?--rossb (talk) 18:34, 5 September 2012 (UTC)

I presume that's one that doesn't work. There isn't much to go on here. Would it be possible to give a link to one that does work, for comparison? Looie496 (talk) 19:34, 5 September 2012 (UTC)

Firstly, try renaming it from foo.JPG to foo.jpg

Secondly, downscale to a web-sensible size - for online display a 3448x2195 2.7MB image is unnecessarily large, and the server has to downscale it when its shown in a page (at least on MediaWiki sites) - you may be running into a conservative file size limit

-- Finlay McWalterჷTalk 19:51, 5 September 2012 (UTC)

Thanks for the suggestion. I think it must be the size - I've scaled it to half the size and now it works OK. I'd been assuming that all my images were about the same size but they obviously weren't: some of them ended up much bigger than others, probably because they'd needed less cropping, and this had probably put them over some limit. --rossb (talk) 20:55, 5 September 2012 (UTC)

You might also take a look at your server's error logs. If it is a cheap server host, you often have a limit to processor monopolization — your site only gets 1% or so of all CPU attention on the rack, and if it tries to get more, it gets temporarily stopped. For most web stuff you don't need a heavy server load, but in my experience, anything that has to do with image processing can be a heavy load indeed. So it may be that when PHP tries to make thumbnails of those big images, it is crapping out the server, and never completing. Just a hypothesis. You should be able to confirm or eliminate this possibility by looking at error logs or CPU usage logs. --Mr.98 (talk) 13:29, 6 September 2012 (UTC)

Tech help

Ok, so I realized I couldn't access http://mesonet.agron.iastate.edu recently and so I sent an email to them. Apparently the IP address I was trying to access the site from (one of the University of Oklahoma ones) tripped their Denial of service filter. They sent me an error they were receiving:

Sep 5 15:59:43 iemvs104 httpd[25812]: [error] [client 129.15.139.206]
Invalid URI in request GET HTTP/1.1

I have no idea what I could be doing that would cause this (I don't even know what the error means). My best guess is running an mIRC script to relay messages from the iembot RSS feeds into my Freenode IRC channel, but I've been doing that since at least the beginning of April with no problems. The script I have been using is http://www.mircscripts.org/comments.php?cid=3585 . Is this something that could be causing the error they sent me, and if so what can I do to correct it? Ks0stm ^{(T•C•G•E)} 21:40, 5 September 2012 (UTC)

I can access the site listed at the top of your post. StuRat (talk) 21:52, 5 September 2012 (UTC)

If there's a place where you entered a URL, try http://mesonet.agron.iastate.edu/ (with the closing slash) rather than http://mesonet.agron.iastate.edu. I think this is caused by a bug in the script, specifically in the lines

     sockwrite -n $sockname GET $regml(2) HTTP/1.1

which end up sending a bogus request to the server when there's no slash after the host name. It would be worth reporting this to the author if you know how, although it looks like the script hasn't been updated in years. -- BenRG (talk) 23:11, 5 September 2012 (UTC)

I would think that may be it except that all the URLs I have the script using are RSS feeds with URLs in the form http://mesonet.agron.iastate.edu/iembot-rss/wfo/koun.xml (with the exception of all of them combined, which is at the URL http://mesonet.agron.iastate.edu/iembot-rss/wfo/botstalk.xml). I'm not sure if there's something I'm missing, but are there other possibilities? Ks0stm ^{(T•C•G•E)} 00:22, 6 September 2012 (UTC)

Shadows on green screens

My local TV weatherman stands in front of a green screen and we see the weather map digitally substituted in for the green screen. One surprising thing, though, is that his shadow appears on the digital substitution. How ? (I would either expect no digital substitution or normal shade digital substitution.) StuRat (talk) 21:49, 5 September 2012 (UTC)

Broadcasting not being my focus in meteorology I'm not for sure, but my best guess is that the darker shade of green the shadow produces isn't replaced as efficiently by the computer as the rest of the green screen...most commonly in my local market it results in a slightly fuzzy, static looking reproduction within the shadow he casts rather than a crisp, clear map or graphic. Ks0stm ^{(T•C•G•E)} 21:57, 5 September 2012 (UTC)

One thought I had is that they may intentionally reproduce the shadow, to make it more realistic, by substituting a darker digital version where darker green colors are detected, indicating that they are in shadow. StuRat (talk) 22:02, 5 September 2012 (UTC)

Now that chroma keying is performed by digital computers (in software, or in specialized image-processing hardware), it is possible to perform arbitrarily complex operations to make the image look nice. For example, a bilateral filter can be used to perform color-masking that is weighted by "amount of green-ness." Nimur (talk) 23:26, 5 September 2012 (UTC)

I've used the hardware used for this. http://www.ultimatte.com/ is the website of the people who make it, if you are interested. 217.158.236.14 (talk) 10:53, 6 September 2012 (UTC)