People often forget how much averaging it takes to get angles accurate to the instrument spec. The definition isn’t intuitive.
https://s3.microsurvey.com/support/Knowledgebase/stderr/Din18723.pdf
And...(I was told) that they used to build the gun to make a certain spec and basically sorted them at the factory based on how they turned out.
Now, the precision is determined by what you purchase. All the guns are 1" and you pay them to not dither the results out to 5". So, in practice, in the past it was common for an instrument to exceed the stated accuracies, but that is no longer the case (according to some of the reps I have spoken to).
Yeah, a lot of caveats there, so, I would like to see an update to this article...
If you don't want to fork out for star*net but have time on your hands the government agency here responsible for survey matters has https://www.linz.govt.nz/products-services/geodetic/geodetic-software-and-downloads/geodetic-software/snap-and-concord-downloads which is free to use.
Tutorial here https://www.linz.govt.nz/products-services/geodetic/geodetic-software-and-downloads/geodetic-software/snap-guidance
I remember years ago in a PLS refresher course (long before I actually had my license) where we calculated the number of angle sets we would have to turn to get a desired accuracy of ±1" per DIN 18723. The results of that persuaded me that a 3" or better gun was the best fit for me, considering instrument cost and type of work I would eventually do. And my comfort level remains at a 3" or better TS.
@ lukenz
Thanks for posting the links.
Equally as important as the accurcay of your instrument is taking the time and admittedly the expense to have it calibrated on a regular basis. It will be an inconvenience to be without it for the time needed but these are the tools we use to make a living. Maintainenance of instruments, rods and tripods is a better investment than increased accuracy.
And…(I was told) that they used to build the gun to make a certain spec and basically sorted them at the factory based on how they turned out.
I think that's basically how CPU manufacturing is handled as well.
Having a better instrument, 1 sec vs 5 sec, will give you higher confidence in your work and it will be more versatile in the long run.
I'm just speculating here, but I would say that a higher accuracy instrument will hold its value better than the lesser alternative.
Here is Australia, you need a 1 sec instrument if you intended to do any serious infrastructure work, it's a spec requirement. If you ever want to do monitoring, a 1 sec instrument is, usually, the standard requirement.
You might only do boundary work for now, but if the economy goes south, you might have to look for work wherever you can find it and having a better instrument gives you more options.
1” total stations are overkill at best (Unless you’re providing monitoring surveys and services on the regular). Field procedures are FAR more important than the difference between a mean angle of 1” vs. 3”. Turning a minimum of 5 sets of angles for control will tell you an amazingly accurate story. Modern robotic total stations are incredibly accurate at turning angles.
And maintenance - OMG. Plz don’t put a 40k+ total station on a cheap tripod, unadjusted tribrach and for the love of accuracy, purchase quality prisms. Put the extra $$$ you would have spent on a 1” total station it into all the parts and pieces that are vital to accurate surveying.
Also, send that total station in yearly or more as needed! We provide loaners for our RTS units while the customers is in the shop. No downtime.
