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Working for a Surveyor that does not understand GPS.
jflamm replied 1 year, 5 months ago 24 Members · 56 Replies
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When the Push Button Was New, People Were Freaked – JSTOR Daily
“You press the button, we do the rest”
Don’t be a button pusher!
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User Guidelines for Single Base RTK Positioning Useful and free from the NGS. The USCOE publication that GeoddMike linked is also worth the price. Van Sickles GPS for Land Surveyors has been recommended and I strongly second that.
Many people treat their GPS units as little more than black box coordinate generators and, mostly, as long as you understand that and the limitations, it is an OK place to start. Just don’t pretend that it is anything else until you understand it better. Everybody has to start somewhere.
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@nate-the-surveyor We use Civil 3D for our drafting and Surveying. I setup all our templates when I got hired and have pretty much been running the CAD since. Before I got here they did all drafting in civil in the model space and never bothered to learn paper space. They used another program for years but I am not sure off the top of my head what it was.
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GPS is easy.
Always, always be sure your basis of coordinates is good geographic data.
There is never a reason to skip using all the CORS, Vendor, OPUS, VRS calculations available to set up any job on good Lat, Long data.
Always project your coordinates to a grid that’s definable, it may be State Coordinates, UTM, a user defined LDP.
My advice is to never, never calibrate, you will thank me as time progresses if you avoid that cluster of madness.
It may be that the company has lots of terrestrial data to merge the GPS with, rotate and translate the old data to the new projection whenever possible, don’t hold the old data and try to make GPS conform to it (it’s sold as the way to do it, but it’s not).
And use a Geoid Model (the latest is the best) even if it means applying a correction to get on local control.
Really, GPS isn’t all that difficult to use and understand, you won’t need to do double differencing calculations.
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My advice is to never, never calibrate, you will thank me as time progresses if you avoid that cluster of madness.
It may be that the company has lots of terrestrial data to merge the GPS with, rotate and translate the old data to the new projection whenever possible, don’t hold the old data and try to make GPS conform to it (it’s sold as the way to do it, but it’s not).
And use a Geoid Model (the latest is the best) even if it means applying a correction to get on local control.
Some really good nuggets there
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My advice is to never, never calibrate, you will thank me as time progresses if you avoid that cluster of madness.
It may be that the company has lots of terrestrial data to merge the GPS with, rotate and translate the old data to the new projection whenever possible, don’t hold the old data and try to make GPS conform to it (it’s sold as the way to do it, but it’s not).
Best advice so far!!
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My advice is to never, never calibrate, you will thank me as time progresses if you avoid that cluster of madness.
It may be that the company has lots of terrestrial data to merge the GPS with, rotate and translate the old data to the new projection whenever possible, don’t hold the old data and try to make GPS conform to it (it’s sold as the way to do it, but it’s not).
That has been my long term policy as well.
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Hmm, I’m going to get really picky here.
My advice is to never, never calibrate, you will thank me as time progresses if you avoid that cluster of madness.
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And use a Geoid Model (the latest is the best) even if it means applying a correction to get on local control.
A calibration can be a way to apply a correction to get onto local control.
If you have a well-defined coordinate system, a single point calibration will give you position and orientation.
And it is easily checked in the field.
Around here our local control is based on ITRF2000 not WGS84 so this a common practice.
It does help to understand what is going on, and the implications, but calibration is just another tool in toolbox
YMMV
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Seeing posts like this makes me really proud of having a 4-yr degree in Surveying/Mapping (no pun intended). In our GNSS class we went through all the steps of working with base stations, receivers, RTK, data processing, etc. Even though the softwares we use are outdated, the general understanding is still there, and it’s a matter of learning and working around with the new softwares. I have no idea about your degree program, but if you have a general idea, grab the bull by the horns, if they provide the training that’s better, if not, find videos on your specific software, do your research.
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Hmm, I’m going to get really picky here.
My advice is to never, never calibrate, you will thank me as time progresses if you avoid that cluster of madness.
…
And use a Geoid Model (the latest is the best) even if it means applying a correction to get on local control.
A calibration can be a way to apply a correction to get onto local control.
If you have a well-defined coordinate system, a single point calibration will give you position and orientation.
And it is easily checked in the field.
Around here our local control is based on ITRF2000 not WGS84 so this a common practice.
It does help to understand what is going on, and the implications, but calibration is just another tool in toolbox
YMMV
I don’t think a single point calibration is what most people are doing. I believe they tie into many control points and hit the button to merge the GPS into that control. I think what you mean is to occupy already projected control and use the point to survey from?
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Multi-point calibrations are common, especially in the engineering and machine-control fields.
They work well when are between you control marks. But outside of there they can introduce distortion that is hard to identify and to document.
If your underlying coordinate system is known and properly defined – like the official NZ circuits, or State Planes, a single point calibration is an easy, rigorous and documentable way to shift WGS84 observations to another system.
Like any tool, calibrations can be dangerous – you need to understand how to use them and their implications
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@jimcox yes, calibration is a useful tool. Definitely requires an understanding of what’s going on when reviewing the report/results of the calibration. Similar to a multipoint resection, you have to be able to identify outliers that add error to your calculated coordinate and delete them.
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We use UTM coordinates and we try to just use that projection for the majority of our newer subdivisions we work in.
But depending on the job and other neighboring subdivisions, we have to do site calibrations (usually multiple points but there have been 2 where I was specifically told by my boss, the licensed land surveyor/owner of the company, to calibrate to one single point). The checks worked.
I suppose if we wanted to just say “No calibrations at all, NO EXCEPTIONS!” we would just have to pass up certain jobs and let someone else that is willing to do it take the job.
After doing a bunch of these and doing checks all over the place, I have a hard time understanding the guys who talk like they’re the worst thing ever.
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After doing a bunch of these and doing checks all over the place, I have a hard time understanding the guys who talk like they’re the worst thing ever.
Consider yourself lucky for working in an area with competent gps control to start from and located where they need to be. We’ve used GPS for as long as I can remember and the only jobs we’ve ever had issues on involved existing jobs we had to calibrate to. Calibrations can work just fine but when they don’t it can be really bad. I’m talking about multi-point calibrations and not a single point calibration. If your project is already on a state plane system a single point calibration is all that’s needed. And that’s not really a calibration IMO, you’re simply occupying a point with data provided by others. Check into some onsite control and you move forward.
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It may be for some people using an existing projection is simpler and if it’s precise enough to be within tolerances then calibration isn’t necessary, which is the case for most work(boundary, topo, machine control). However, for layout on a large site that consists of several systems that are tied together, then calibration is generally necessary to get the precision required. I’ve also known PM’s that would discourage calibrations due to the risk of something going wrong and would argue that the reduced precision of SPC outweighed the risk of a botched calibration. I also believe it depends upon the region your in and the difference in scale factor between regions. I know surveyors in areas that it’s not worth the time calibrating for the little difference in precision and I know surveyors in areas that have to calibrate for certain jobs. NGS gives a good idea of areas a calibration might be necessary for certain jobs or if SPC is precise enough to meet tolerance requirements for the job.
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I suppose if we wanted to just say “No calibrations at all, NO EXCEPTIONS!” we would just have to pass up certain jobs and let someone else that is willing to do it take the job.
After doing a bunch of these and doing checks all over the place, I have a hard time understanding the guys who talk like they’re the worst thing ever.
I don’t think the previous comments meant that at all. I agree 100% with what was said and calibrate output data all of the time. If you don’t not understand them, use them for data collection, don’t anaylize your raw data and merge them with prexisting data, then yes, THEY ARE THE WORST EVER.
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However, for layout on a large site that consists of several systems that are tied together, then calibration is generally necessary to get the precision required.
Red flags, bells, whistles, flashing lights…
You type so nonchalantly, so loosey-goosey, about SPC, site calibrations, etc., it makes me wonder:
How large of a site are you talking about?
How many is “several systems that are tied together” and what does that even mean?
What type project (civil?) are you working on that requires layout precisions exceeding SPC? I know those exist, but generally, those unique situations are very local.
I pray you are not using GPS/GNSS to layout buildings, bridges, or steel?
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Yes I understand that. When we do a calibration all the data is checked by the office before we start doing any layout. This is typically done at the beginning of a new phase of a subdivision.
I’ve seen other guys that won’t do a resection but they will setup and backsight a point 40 meters away and shoot a point 60 meters away, then check into another control point, say it’s 3cm off or 0.09ft off, and say well there is nothing I can do about it…it’s close enough.
In that case I’d rather try a resection if I can do one with multiple points surrounding where I’m working….even if it’s using a few existing building corners, and then often I’m checking less than 1cm to everything around me.
I say this just because resections and sits calibrations are very similar.
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@michigan-left I apologize I got a little off topic I was talking about site calibrations in general not just GPS however there is obviously a need somewhere or their wouldn’t be LDP’s no I don’t use GPS for layout other than staking corners for clearing or digging footers/basements was that less loosely goosey enough
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