Apparently, TAI specifically defines the second (in terms of cesium transitions) at sea level (where gravitational potential is equal). I never knew that second part.
If you want to go further down the LIDAR path, you might be able to improve the public data by making manual improvements to the point cloud classification.
For that sort of terrain it's common for classification algorithms to put vegetation (e.g. deadfall, small bushes) into the "ground" class, so when the terrain model gets triangulated using all the "ground" points there is erroneous bumps. If this is the case, you could reprocess the point cloud yourself and tweak the settings being used or make manual adjustments.
I'm not sure of the quality of the linked dataset, so maybe it would be difficult to find improvements. But you knowledge of on-the-ground conditions (and smallish scale of the area) means it's definitely possible.
Also, just in case you haven't stumbled across it, a "Digital Surface Model" (DSM) is different than a "Digital Terrain Model" (DTM)!
(surveying student here, very much enjoyed the writeup!)
GPS determines a solution for position and time simultaneously. It requires 4 satellites to solve for 4 unknowns (X, Y, Z, t). If you know your position you can solve for time using only 1 satellite, but a watch is always moving so it's position won't be known.
Edit: I would welcome corrections though if I am misunderstanding. Perhaps if you're not interested in precise timing you can read the satellite time from the broadcast signal?
Edit 2: OK, I think I understand your point now. The satellites broadcast their timestamps directly. To find a precise position / time you need to find a correction to the receiver clock. But if you don't need a very precise time, you can just use the satellite timestamp.
A group of students at my university were claiming their papers were being marked by a LLM. They cited a classifier like the OP which they used on their feedback comments.
A friend of mine once described this as a "critical hit chance" (ala video games). There's not much chance of a 'critical hit' if you're just hanging around home, for example. But if you're on the road, stopping in at a random pub for dinner? There's that chance something special happens.
Sometimes it might be better to trade the option with higher average damage for one that is more volatile, because you might get lucky at just the right moment.
> What the US government did was remove the bias from the CA code so it could be used for precise positioning. The military still uses P codes as well. I believe there is a small gain to be had but it’s due to frequencies.
The precision of positioning from the P code is 10 times greater than the C/A code (about 30cm vs 3m). This is due to the wavelength/'chip length' of the code signal which is modulated onto the carrier wave (10.23 Mhz / 29.31 m wavelength for P code, 1.023 Mhz / 293.1 m wavelength for C/A code). Positioning precision is limited to about ~1% of the chip length by signal processing.
This is correct, but I'd like to add that at some point the errors from which frequency and code you use is no longer the dominant factor in the position error. Depending on where you are, either multipath errors (eg due to reflections from buildings or mountains) or athmospheric errors (ie due to the radio signal being distorted in the ionosphere) start to dominate.
I'm a first year Surveying student, after I spent all of high school thinking I'd study computer science / software. I don't see much discussion of the topic on HN so I'm glad this is getting upvoted!
The opportunity of working outdoors appeals to me a lot, as does the technology (drones, remote sensing, GIS). It also seems like a much more relaxed job market than a more traditional tech / engineering job (albiet with less pay).
I'd love to hear any thoughts on the profession or suggestions for those early in their career.
Books are your friends. I used to use the down time (bad weather, equipment being moved out of the line of sight) to read surveying books that I kept in the truck. Also, it's to your advantage to brush up on your trigonometry. You'll need it.
I started working on building sites, not as a full-time surveyor, but had to learn doing many of the typical surveying measurements, just around the time the "technical revolution" came, early 1980's.
#1 - laser (or whatever) distance meters, until then there were only Invar stadia rods and staffs [0]
#2 portable calculators (before the ubiquitous HP-11c, there was the HP-67 or 97, but right until then it was logarithms books and manual calculations)
Then, like only a few years later, I believe 1989 or 1990 came:
#3 "real" total stations, with an actually working interface to computers, that changed once again the way we could work, much, much faster [1]
Still, it happened more than once to need (for one reason or the other, dead batteries, tools shipped for revisions, and similar) to need to do manual measurements and surely you need to have your basic trigonometry brushed up.
[0] here is an early Kern one, it costed (not the "full" E1 deopicted, only the DM503 + a "conventional" theodolite) at the time around 32 or 34 millions Lire, more or less like 2 years of a surveyor wage:
The HP-48x with a COGO card in the slot was a big advance for me; I learned on a Wild T3 theodolite, so advanced total stations with a data colletor such as the Leica were a big step up in productivity as well.
Yep, but the 48 came out a few years later, in the early '80's all we had were 67 and 97, then the 11C that was actually "portable" and with everlasting batteries, the "main" product at the time was the 41 but it was heavier and bulkier (and costed a lot more than the 11C, which was also nearly indestructible, I mean we had a couple of times wheel loaders passing on one of them and it came out only slightly bent in one of these incidents).
Right after the 41 and 11c, but before the 48 came the 28C (which also costed an arm and a leg, but I still have my beloved 28C in use, prefectly working, some thirty years later, so it wasn't such a bad investment ).
Do you learn about the history of surveying as well? I'm super interested in how people surveyed the land for early bridges or for the purpose of cartography.
I'm quite early in the course, so couldn't give you a good answer sadly.
The intro to surveying class had a very broad overview of the history- important technologies, discoveries, and figures.
There is a Surveying and Engineering Law class that I expect will contain a lot of historical cases. Otherwise, there are no specific classes, so any history will probably be dispersed throughout the degree.
Apparently, TAI specifically defines the second (in terms of cesium transitions) at sea level (where gravitational potential is equal). I never knew that second part.