Hey guys,

Just wondering how one would go about setting up a new base control point for use in a mine surveying scenario using a Trimble dGPS.

A previous surveyor who used to work here knew how to do it, but I do not. He mentioned something about setting up the equipment and then running static observations for several days? That's about the extent of my knowledge as it stands.

So I'm after any advice in doing this, or if someone could point me to a how to article or online guide that would be very much appreciated.

Cheers.

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The answer to that varies based upon what you are trying to do. Is it supposed to tie into an existing control network or are you starting completely fresh?

If you are using an R8 and setting a fresh point, I'd collect a half a day of data or more and submit an OPUS solution to NGS to get State Plane Coordinates.

If you are just setting something local for a new job, you can just hit the "here" key and record those coordinates to be used for that point.

Do you have a base and a rover? access to an RTK network?

There's all kinds of answers to your question because it based on demands of the project.

Well there is an existing base point nearby that we have been using for survey work, but it is simply a metal peg in the ground that we have to set a tripod over every time we want to use it. So we installed a steel post into the ground with concrete (and also core filled it with concrete) and welded a thread onto the top that the base unit can screw onto. That way we do not have to bother with the tripod each time we need to do some survey work.

But now we have to setup a new base point over the core filled concrete post, so that we have a more permanent base setup.

Yes we have a base and a rover. Not sure what an RTK network is, but we have been using an existing base point in the area previously to do surveying, but as I said we wanted something a little more permanent than a peg in the ground.

Thanks for the help.

Ok. So to basically be on the same coordinate system as that peg, you'll need to do a single point transformation, or what most contractors would call a localization.

Basically, set your base up in the new point and just hit the "here" key when you start it. Now go into the whatever projection/transformation/localization program your data collector has for your Rover and go measure that old peg. Then it'll ask you what the coordinates you originally had for it and it will move your new base to the coordinates that match the observations between the two points. It's better to do this with multiple points, but it sounds like you've been using just one.

From there on, you'll just take that localization and put it to your jobs to keep it on the same system. I would definitely set a couple more iron pins in the ground should your base point get disturbed.

If you wanted to get it to a state plane system, you can just log the raw data on it while you're doing this and export a RINEX file using the Trimble software you likely have. Take that RINEX and upload it to the OPUS page with your recorded height and voila. You'll receive an email with all the information about your new base point.


Another way would just be to setup on your old point like you usually do, then take your Rover head unit and screw it onto the new location. Take a shot using a fixed RTK (which means it's initialized from receiving corrections) solution. Now you can move your base to that point and use the coordinates you just shot.

It doesn't sound like you're after a lot of accuracy, so what I've answered will probably do what you need

Ok thanks for the help William that sounds pretty straight forward.

On a side note, will the static obs method not work? Or is that not really what static obs is designed to achieve?

The static achieves basically an Opus solution on a single point. Static is more for making entire networks of control where you have 3 or more units occupying points.

RTK (which is what you're doing by using a base/rover) is just as accurate because you're already coming from a known point.

You would do a static GPS survey of there wasn't control at all basically

Ok things are starting to make sense now. So what degree of accuracy would we be looking at if we were to do RTK? Because while we may not need a high degree of accuracy at the moment, this point will be a permanent base point and so someone may need a high degree of accuracy later on down the track.

You'll have basically the same degree of accuracy you had before, I think. In order to establish a very good quality you´d need a static survey tied to at least 2 more points with known coordinates. Normally I prefer 3 points to enclose the point I want to know. Then you'd have to swing the antennas to read the multiple triangles sides simultaneously. From my experience this is very accurate, way below 5 mm.

However, if that base is intended to be a common point for you and other surveyors, even if an error exists, that possible error will be common to all, therefore negligible.

Jose is correct. We are talking within a half inch of accuracy basically. Repeating and averaging over multiple days will also help.

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