elfchief (u/elfchief)

elfchief commented on Nvidia Unveils Path Tracing Demo from CES/GDC 2025 – Now Available for Download brightstack.blogspot.com/... · Posted by u/lamariexa

elfchief · a month ago

The linked article is awful -- it not only doesn't contain a link to the demo (just to "nvidia.com"), but it doesn't even say what the name of the demo is... plus there's a couple of different places where the article just randomly links to some random person's soundcloud...

For those looking for it, I think this is referencing the "Zorah" sample, from https://developer.nvidia.com/rtx-kit ... though at this exact moment, the download link on that page seems broken. Failures all the way down, I guess.

elfchief commented on Cheap rj45 ethernet to USB adapter contains malware twitter.com/evapro30/stat... · Posted by u/rsecora

elfchief · 8 months ago

It's worth noting that there's basically zero proper evidence that there is any malware included with this device -- it runs an exe when inserted, but that exe appears, at a glance, to be a driver installer. Definitely not the right way to do things, but there's a difference between "incompetent" and "malicious".

The only actual "evidence" that was provided was a link to a falcon sandbox run, something which actually requires human analysis to draw conclusions about -- and anyone who has ever used it knows how many false positives it finds.

A better proclamation might be "cheap network adapter comes with an auto-running executable which needs further analysis".

elfchief commented on A SpamAssassin Surprise lwn.net/SubscriberLink/98... · Posted by u/rwmj

elfchief · a year ago

I really wish I could move my personal email over to gmail -- I've run my own local email server for 30 years, and tbh I just don't really care to do that anymore.

But I'm stuck -- I exclusively use 'tagged' email addresses when giving anyone my email address, so every incoming message is addressed to "myusername-sometag@domain"... and gmail, of course, uses a + instead of a - for doing that kind of tagging. So if I tried to migrate hosts, literally none of my incoming email would arrive anymore.

Sucks that a decision I made before gmail even existed now restrains me so much. :/

elfchief commented on GPS vs. Glonass vs. Galileo gpsrchive.com/Shared/Sate... · Posted by u/cokernel_hacker

adgjlsfhk1 · 3 years ago

your main sources of error will be from the Earth's atmosphere and signal bounced which both change the time signals take to reach you. there are pretty hard lower limits on the amount of error. gps already has to deal with relativistic effects to get as accurate as it is.

elfchief · 3 years ago

To expand on this for @causi: The largest thing is the earth's atmosphere, because changes in the ionosphere (and a lesser degree, the troposphere) cause the signals to get refracted differently from moment to moment. Part of the data coming from the constellation includes general ionospheric correction data (and WAAS can provide data that covers smaller (but still kinda large) areas, which allows the receiver to adjust for those refractions to some degree, but there's only so much it can do -- conditions change quickly, and in areas smaller than the correction data can accommodate, so there's still variance that can't be completely removed -- it's not a lot, but at one foot per nanosecond of delay, it can still make a significant difference.

At least, that was generally the case until recently. There is actually a way to almost completely remove the effects of both the ionosphere and troposphere: Those things affect signals differently if you have multiple signals at different frequencies. And, as it happens, GPS does actually have multiple frequencies (L1 and L2, and now L5 as well), and for a fairly long time there have been receivers that could listen to signals from the same satellite but different frequencies, and based on the delay difference between those signals, know exactly what the atmosphere was doing at that exact moment, and dial out the influence of the atmosphere almost completely. You can start getting pretty durned precise once that's not a factor.

The problem is that multi-frequency receivers used to be expensive. Like "started at $10k for the cheap stuff" expensive, even within the last decade. Only in the last few years have inexpensive (under $100) chips become available for doing multi-frequency GNSS. And those can get down into the "under 1 meter in realtime" range trivially, and better than that for a fixed-location station. Phones are getting these now, so things should start getting more accurate, though not that much more accurate.

Multipath is also a big problem in "the urban jungle", but chips are getting better at discriminating, and unless you're just utterly surrounded by skyscrapers, usually isn't too big a deal.

Orbital calculations are also another cause of loss of precision -- the orbits are calculated pretty precisely, but for various reasons the ephemeris data sent down from the satellites doesn't actually represent exact orbital data, but represent data that's "good enough" over the couple of hours the ephemeris data is valid. This can be worked around with patience -- there are ground stations around the world with exactly surveyed locations, which monitor the satellites and calculate the exact orbital paths the satellites actually took, and publish that data (though it takes several weeks to get the "final" data). A typical surveying technique is to record several hours of data from an antenna at a survey location, and then when the precision orbit data is published, post-process that recorded data to remove both orbital and ionospheric effects. This can get you down into the sub-cm range, with enough care.

And then there's also a range of other factors, like solid earth tides, which cause the land masses of the earth to rise and fall by up to a meter(!!!) over time, and when you're trying to figure out exactly where a given point in space is on this big rock ball, that matters!

But, yeah, pretty much it's atmosphere, unaddressed multipath, and orbit precision that makes the difference, and the above is how those are usually dealt with.

</ramble>

elfchief commented on GPS vs. Glonass vs. Galileo gpsrchive.com/Shared/Sate... · Posted by u/cokernel_hacker

avianlyric · 3 years ago

Out of interest are speaking from a position of authority as someone who’s implemented GPS receivers, or as someone who understands the theory of GPS receivers?

From my reading of the article, it sounded like the author was commenting on an interesting implementation detail of GPS receivers, and how they might deviate from their expected theoretical implementation. Rather than describing how an ideal GPS receiver is implemented.

elfchief · 3 years ago

There's pretty much never a reason (...normally, but see below) you'd use a separate satellite for the time -- you do need four satellites to solve for X/Y/Z/time, but you solve them together. Basically, there's only one combination of satellite positions and (pseudo)ranges that will produce a solution, and one of the outputs of that solution is the time (the inputs are just time offsets between the various signals, based on the receiver's non-precision local clock).

The see below part: There are timing receivers that will do a long "survey" to figure out their exact location (or as close to it as they can), and once they have that they can use a single satellite to determine the current time, since they already have most of the needed equations "solved" when the receiver already knows its own (static) location. This is sometimes preferable, depending on one's application, because it makes for less jumpiness in the time solution as new satellites go into and out of view (since the changing geometry of the constellation will make for slightly different solutions every time it changes)

elfchief commented on Falcon Heavy Launch [video] spacex.com/launches/ussf-... · Posted by u/mpweiher

BitwiseFool · 3 years ago

>"wasteful to see that mission profile with the center booster burning up without even trying."

My understanding was that the intended orbit / mission profile means that they must fly the center core in expendable mode. Otherwise, the satellite wouldn't be able to reach the intended orbit with the intended amount of fuel for the mission's duration.

elfchief · 3 years ago

At one point (I don't know if it's still the case) for certain launches the US government laid claim to "100% of the thrust available from a booster" or somesuch, basically not leaving anything left over for landings. I'm not sure it was ever documented why they had this requirement.

What surprised -me- was that all three boosters were brand new, rather than, say, expending a booster that's already flown half a dozen times or such.

elfchief commented on Ask HN: What colorscheme are you using in your code editor? · Posted by u/navierstokess

elfchief · 3 years ago

I'm impressed at just how hard it is to see what catppuccin actually looks like in VSCode without installing it first. The catppuccin github has no screenshots, and the catppuccin-for-vscode github/site has exactly one screenshot, which is split into diagonal "bands" for the four different versions of the scheme, and only one of those bands has a significant amount of code.

elfchief commented on Why does the US allow a controversial weedkiller banned across the world? theguardian.com/us-news/2... · Posted by u/elorant

elfchief · 3 years ago

I think the answer to literally every question that starts with "Why does the US..." is going to always be: profits

Profits are the only yardstick by which anything in the US is measured. Everything else is secondary.

elfchief commented on Flying the Unflyable Plane: The near crash of Air Astana flight 1388 admiralcloudberg.medium.c... · Posted by u/mhandley

deeblering4 · 3 years ago

It seems color coded cables would be a nearly zero cost solution. I wonder why identical steel cables were preferred, and how this wasn't an issue in manufacturing?

elfchief · 3 years ago

I suspect having a color coding material/technique that can apply to random bits of random plane parts, that won't get rubbed off / broken off / obscured by dirt/grease/grime/etc, consistently throughout the plane, is probably harder than it appears at first glance.

elfchief commented on iPhone 14 Pro comes with dual-frequency GPS apple.com/iphone-14-pro/s... · Posted by u/tosh

Waterluvian · 3 years ago

L1/L5.

elfchief · 3 years ago

Neat, if so! Where do you see that, though?