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For $20, Build a VR Headset For Your Smartphone

CityZen Field of View (49 comments)

Half-baked solutions like this will have limited field of view (among other shortcomings). In order to get a wide FOV (which is important for immersion), Oculus is using very powerful aspheric lenses, which necessarily result in a distorted image. The distortion is "undone" by doing a pre-anti-distortion of the desired images prior to displaying them on the screen.

Latency will be another big issue, especially from tracking using a webcam that's probably running at 30hz.

I think that this stuff is great for experimenters who want to get a taste of VR on the cheap. However, it is a far cry from well-engineered setups.

2 days ago
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Switching From Sitting To Standing At Your Desk

CityZen It's not binary (311 comments)

Obviously it's a problem to sit all day. But it's not a binary decision between sitting all day and standing all day.

Like everything in life, the key is "balance": not too much, not too little.

Keep using a chair if that's what you like. Just be sure to stand up, stretch, stroll around a bit periodically.
Set a timer if you need to remind yourself.

If you like to stand, that's fine too. You also need to move around periodically, or even sit down.

5 days ago
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Algorithm Challenge: Burning Man Vehicle Exodus

CityZen Re:The playa exit is not the problem. (273 comments)

Then the answer seems obvious: Schedule the last day's events in order from most to least interesting, making sure to have a decent progression towards inanity as you get towards the end. People will naturally trickle away, as they decide the next events are not worth attending. (Perhaps the whole week should be scheduled with the most interesting events in the middle, and the more inane towards start and finish.)

Another possible answer comes up as well: treat the exit line like a Disney theme park entrance line: make it interesting enough to be in, but never interesting enough to hold anyone up.

about three weeks ago
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Ask Slashdot: Experiences With Free To Air Satellite TV?

CityZen Re:I use Linux (219 comments)

> Never the less Linux has excellent support for various DVB/ATSC hardware.

One reason for this is that many receivers (set top boxes) use Linux as their internal OS.

about three weeks ago
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Ask Slashdot: Experiences With Free To Air Satellite TV?

CityZen Re:Are you in the USA? (219 comments)

Lyngsat is the best place I have seen to get information about what programming is available. However, its organization takes some getting used to.

The page linked above shows the programming that originates from the US but is broadcast around the world. Similar pages can be used to find programming originating from other countries. However, you need to understand what satellites are viewable from your location.

Other pages are those that show what's available from satellites you can see, such as: http://www.lyngsat.com/america...
This page shows the satellites that broadcast to the US, ranging from 61.5 W way over toward the east to 139 W way over toward the west. If you are located on the east coast, you may have trouble receiving 139 W unless you have a clear line of site toward the west and a perhaps larger-than-typical dish. Similarly, if you are located on the west coast, you may have trouble receiving 61.5 W. Satellites that are more directly overhead your particular longitude will typically be easier to receive. You can find your own longitude very easily by googling your zip code plus "longitude".

Once you're looking at a particular satellite, say Galaxy 19: http://www.lyngsat.com/Galaxy-...
then you need to understand the information that's presented. The first table lists frequencies in the ~4000 range, which corresponds to C-band. To receive these, you need a "BUD" (big ugly dish) of size 6-12 feet (2-4m). The next table lists frequencies in the ~12000 range, which corresponds to Ku-band. These can be received with a 30" (0.75m) dish.

The next columns to pay attention to are the provider name and the system encryption. Look for the "F" icon in the encryption column, indicating that the channel is FTA. Also confirm that the first entry for the transponder in question shows "DVB-S" (or "DVB-S2") and that this is compatible with the receiver you have. The first entry provides info about the multiplexed stream, whereas the subsequent entries provide info about each individual channel within the stream. A decent receiver will be able to figure out all these details itself, but older hardware requires programming in some details.

There's really a couple of ways to use FTA. One is to just set up a system locked to a given satellite and stick with a channel or small set of channels that are stable. The other way is to hop around different satellites and see what's available, since programming does change over time. For this, it's important that your receiver has "blind search" capability (which should be pretty common by now, but you should verify). Having the ability to program the channels easily with a computer program is another nice feature that many receivers offer. This can be a lot better than fiddling with the remote and endless menu layers. And, of course, a motorized dish mount makes it easier to change satellites.

A final word before you embark on this: Lots of these channels have online viewing options, which can be much less frustrating to view (or they can offer a different type of frustration). At least you won't have to fiddle outside with dish alignment on a rainy day to peak the signal. You can instead learn about proxies from the comfort of your desktop.

about three weeks ago
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Ask Slashdot: Re-Learning How To Interview As a Developer?

CityZen A couple of tips, based on a recent interview. (218 comments)

When I interview someone, I ask them to explain something to me. A good candidate can provide a concise overview of the topic and then work through it in a coherent manner, seeking and taking in feedback from me to see if they're explaining things at the right level. Just wandering around the topic isn't so good. It's okay to say what you know and what you don't know.

Another thing I do is to ask them to solve a problem (either a simple but slightly tricky coding problem or a problem about a technology we've discussed). What I like to see is someone who can explain their thought process as they go. If they get stuck, they should be asking questions. But just sitting there thinking quietly isn't a good sign, especially when they don't come out with a good answer eventually.

You do need to find a good balance between talking too much and being too quiet. To do this, it is important to seek feedback and take queues from the interviewer. This kind of interaction is key to "working well with others".

about 1 month ago
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How Do You Backup 20TB of Data?

CityZen Re:Hmmm... (983 comments)

The 6.25TB is "compressed" capacity, while the "native" capacity is 2.5TB.
That tape cartridge will cost you about $70, plus you need a drive for it (about $2000).
A 3TB hard drive goes for about $100.

To handle 20TB:
7 x 3TB HD's = $700.
8 x 2.5TB tapes + 1 tape drive = $2560.

You'd need quite a few copies of the data before the tape drives make more sense economically.

about a month ago
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I'd prefer military fiction books that are ...

CityZen Doesn't matter (236 comments)

It's the writing and characterization that matter.

I loved Patrick O'Brian's Aubrey-Maturin series, set in the 1800's. There was a bit of tedium initially in his detailed descriptions of sailing procedures, but his lively characters made it worthwhile, and eventually even the sailing bits became interesting once you became more familiar with the topic.

about 2 months ago
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A Strategy For Attaining Cuban Internet Connectivity

CityZen What's their cell phone strategy? (119 comments)

Wouldn't it face the same issues?

As far as internet, the people may wish to look at mesh wifi setups.

about 2 months ago
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Dead Reckoning For Your Car Eliminates GPS Dead Zones

CityZen Re:I work for an automotive telematic unit supplie (151 comments)

Why 3D? Because some places have lots of elevated highways (as well as parallel roads underneath them).

But mostly because GPS works in 3D, and re-acquiring the signal is faster the more accurate the 3D estimated location is.

about 2 months ago
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Yota Phone Launches With Secondary E-Ink Display

CityZen Pixel Qi? (72 comments)

Yes, why don't many more devices use the Pixel Qi display? You know, the one that's a normal color LCD when backlit, or a monochrome very-low-power LCD when front-lit (ie, by ambient lighting). Seems like it would be ideal for phones and smart watches.

about 5 months ago
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The Science Behind the InfinitEye's Panoramic Virtual Reality Headset

CityZen Single FOV number no longer adequate (42 comments)

With these somewhat asymmetric FOVs, a single number doesn't provide enough information to understand what you're getting.
What's needed now is the "inside angle" and the "outside angle", where:
- inside angle = how much either eye can see toward the other eye
- outside angle = how much either eye can see away from the other eye
(in either case, measure the angle from "straight ahead" over to the cut-off point where you can no longer see anything)
In a symmetric system, both of these numbers are the same (or pretty close, anyway); you'd just add the two to get regular FOV.
You don't want the inside angle too small, or else you'll feel like you've got a huge nose (or your hand between your eyes).
Making the inside angle large is complicated by the fact that the displays will run into each other.
Making the outside angle large is easy by comparison.

about 5 months ago
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CMU AI Learning Common Sense By Watching the Internet

CityZen Re:It's learning common sense? (152 comments)

You can learn lots of common sense from the internet:

- Whatever you see there, learn *not* to do!

Since mostly we post the epic failures of others, this technique will increase survival skills dramatically.

about 5 months ago
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Two Sailors Injured When Drone Crashes Into US Navy Guided Missile Cruiser

CityZen Note: No baking popcorn using ship's radar (109 comments)

Please use only the oven specifically designated for this purpose. Thank you.

about 5 months ago
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Alfred Poor Says HDTV Manufacturers are Hurting (Video)

CityZen Re:pointless (307 comments)

I'm sure you could tell the difference between high-bitrate content made to make 4K look good vs. ordinary compressed HD content.
However, if you were to watch the same content with appropriately-high bitrates for 4K and HD, you probably wouldn't see the difference.
Why would they try to make both sets look as good as possible if the point is to sell the more expensive one?

about 5 months ago
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Alfred Poor Says HDTV Manufacturers are Hurting (Video)

CityZen Re:pointless (307 comments)

I think he meant 6K bits, not bytes, since 16 lines x 64 columns x 6 pixels/character = 6K binary pixels.

about 5 months ago
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Demo of Prototype Virtual Retinal Head Mounted Display

CityZen Re:pretty epic (93 comments)

You didn't catch the part where you can attach a "screen" directly to the goggles to achieve VR.

about 5 months ago
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Demo of Prototype Virtual Retinal Head Mounted Display

CityZen How you see, how displays work, etc. (93 comments)

Let's see if we can clear up a few things. Imagine looking at your monitor.

The pixel in the upper left corner is emitting a hemisphere of light. Or rather, it's emitting a bunch of rays of light that spread out in a hemisphere. Under ideal circumstances, it's the same color and intensity for any of those rays, though we know from experience that it tapers off and sometimes changes color as you see it from greater angles. But for most of the "straight on" angles, they're about the same.

A subset of that hemisphere of rays is entering one of your pupils. If you consider the shape of that subset, it forms a cone, with the base at that pixel on the monitor, and the extent formed by the circle of the pupil. All those rays of light will (assuming your eye is focused on the monitor) focus to a point on the associated retina.

The individual rays in that cone are close to, but not quite, parallel to each other. The farther away your monitor is, the more parallel they are, and the closer the monitor is to you, the more the rays are spreading out. Each eye's lens takes care of focusing the parallel or spreading out rays back to a point on its retina. Note that if the rays are spreading out too much (ie, the monitor is too close to your face), you cannot refocus the rays back to a point. You'd need additional optics to help achieve this. (This is why Oculus needs a big fat lens in front of each screen.)

For the purposes of this explanation, we'll simplify a bit and consider a bundle of rays that are parallel. Given this simplification, the only distinction between the pixels on the monitor (aside from their color and intensity) is that they arrive at your pupil from different directions.

In fact, you can replace the monitor with physical objects that are reflecting light, and the same principles apply. Going a step further, you can see that it doesn't really matter how those bundles of rays are generated; the only thing that matters is how they enter the pupil. The direction (ie, angle) that they enter from determines the location, and the color and intensity determine what you see there.

So let's take away the monitor, and instead imagine other ways that you can generate different parallel ray bundles directed at your pupil. The original "virtual retinal display" from the University of Washington was based on the following principle:
1) Generate a single collimated beam of light rays. Collimated means that all the rays within the beam are parallel (or close to it). Beam, in this case, does not mean a tiny dot, but rather a beam with some girth to it (on the order of a centimeter).
2) Use one or more tiltable mirrors to shine this beam at different angles at your pupil. By redirecting the beam in a raster-scan fashion, you can trace out a complete image.
3) For each different direction scanned (ie, each pixel), you also need to change the color and intensity of the beam appropriately (to correspond to the pixel you see from that direction).
Note that the beam has to be spread out significantly from a single point, such that when redirecting it from one extreme to other that it will still hit your pupil. Light that doesn't enter your pupil is wasted.

This is just one method. The subject of today's article appears to use a DMD array instead of one or two scanning mirrors. Assuming that the DMD mirrors can scan in a 2D fashion, then it's really the exact sample principle.

Note that there are many other ways to achieve the same ends. If you have a point light source, you could use a parabolic mirror to generate a large collimated beam. Provide some way to scan that beam, and voila. You might also note that spherical mirrors approximate a parabola, except for arbitrary directions. Provide a way to scan the light source, and voila.

As you can see, the trick is mainly in the scanning, since all the rest is "easy".

about 5 months ago
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Demo of Prototype Virtual Retinal Head Mounted Display

CityZen Re:Retina burn (93 comments)

While the video offers lots of BS, the possibility of retinal burn is probably zero:
1) They use an LED, not a laser diode.
2) The light from the LED is spread over a DMD (digital micro-mirror device); it is not a line/dot.
I'd imagine the worst that you'd see if something locked up is a solid color virtual screen.

about 5 months ago

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