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Not that I mind--this is one of the more awesome articles submitted to HN or really anywhere.
It blows my mind that all that complexity is baked into your smartphone
Interesting resubmission. Originally submitted >500 days ago, but today's submission simply put a # at the end of the URL, and thus avoided duplicate detection. Not that I mind--this is one of the more awesome articles submitted to HN or really anywhere.
Interesting resubmission. Originally submitted >500 days ago, but today's submission simply put a # at the end of the URL, and thus avoided duplicate detection. Not that I mind--this is one of the more awesome articles submitted to HN or really anywhere.
Perhaps the resubmission is due to the May 2013 update on the page.
Earlier quoted context omitted.
Good point. Any idea what ballpark speed one would need?
Speed of the FPGA? FPGAs are given speed grades, but the actual design dictates the max speed. Different logic sections, depending on pipelining, size, which pins they are connected to can run at different speeds. You might have an overall max speed/critical path of say 50mhz, but you might be able to safely run a small section of the design at 200mhz.
That page is amazing. I'm astounded that someone can build a GPS receiver from scratch, not to mention writing the code that interprets the GPS signals. The difficulty is mind-boggling! There's some wonderful quotes in the page that just hint at the complexity involved: "Originally, by not transforming satellite positions from earth-centred-earth-fixed (ECEF) to earth-centred-inertial (ECI) coordinates, I was effecti…
This is immensely impressive. What strikes me is that the math and all the corrections would not be all that alien to a sextant user from 100 years ago. To determine position using a sextant you also start with an estimated position and an accurate clock. You compensate for drift during your measurements, for dip and refraction, you solve the equations for several celestial bodies etc.
That page is amazing. I'm astounded that someone can build a GPS receiver from scratch, not to mention writing the code that interprets the GPS signals. The difficulty is mind-boggling! There's some wonderful quotes in the page that just hint at the complexity involved: "Originally, by not transforming satellite positions from earth-centred-earth-fixed (ECEF) to earth-centred-inertial (ECI) coordinates, I was effecti…
This is immensely impressive. What strikes me is that the math and all the corrections would not be all that alien to a sextant user from 100 years ago. To determine position using a sextant you also start with an estimated position and an accurate clock. You compensate for drift during your measurements, for dip and refraction, you solve the equations for several celestial bodies etc.
Some back-of-the-envelope numbers (and precision calculation) here: http://physics.stackexchange.com/questions/1061/why-does-gps...
Earlier quoted context omitted.
Perhaps the resubmission is due to the May 2013 update on the page.
Oh, likely, but the duplicate detection is based on URL matching, not on newness of content. See the other submission at https://news.ycombinator.com/item?id=5717674 and note that the referenced URL does not have the # at the end that this one does.
Earlier quoted context omitted.
This is immensely impressive. What strikes me is that the math and all the corrections would not be all that alien to a sextant user from 100 years ago. To determine position using a sextant you also start with an estimated position and an accurate clock. You compensate for drift during your measurements, for dip and refraction, you solve the equations for several celestial bodies etc.
Except for one thing. GPS computation is one of the few things we deal with in daily life that actually requires relativistic compensation to be accurate. The satellites are moving so quickly (relative to the receiver) and experience such less gravity, that the rate of time passing for them is measurably different than the rate of time passing for the receiver. Enough so that if you did not compensate for the differe…
Earlier quoted context omitted.
This is immensely impressive. What strikes me is that the math and all the corrections would not be all that alien to a sextant user from 100 years ago. To determine position using a sextant you also start with an estimated position and an accurate clock. You compensate for drift during your measurements, for dip and refraction, you solve the equations for several celestial bodies etc.
Less than 100 years ago, GPS wasn't a nav tool until the mid 90s. Astro nav was the standard right up until then and is still taught to masters today. We have calculators for atmospheric diffraction but the long hand method is still used.