CSS I'll second that.
I carry the Disto about doing RTK stuff and a compass and its not many places I am stuck for a measurement.
Wayne,
I get what you're saying. I think you're talking about measuring to a discrete object like a pipe or something, from two different points, and then calculating the position of the object using the dist-dist intersection routine. Yes, I've done that many times. However, the application I'm dealing with is measuring the location of a stone wall that might be 20 or 25 feet from a point where the prism pole might be conveniently located for a shot. It's a little different with something indiscrete like a stone wall, because you can't really see the "point" from the prism pole, you have to go in an figure out where the approximate center of it is. Getting fussy with two shots to a point in the centerline of the stone wall and using a dist-dist intersection is relatively meaningless. The extra time isn't worth it.
Problem is offsets need to be horizontal. Can be slope
Big Al if can get with in a metre then usually tape is rigid so read distance at pole.
If larger distance can, depending on where anchor end tape read two distances. First to the pole for all distance measured and then if end tape anchored on line passed point offset to be measured then plumb corner eg cl post at same height as all, then read that distance. Subtract two for offset. Some times if on ground I anchor tape with chaining arrow or a steel footing rod if off ground.
Anchoring at pole is not advisable if solo operator as will easily pull pole off vertical.
RADU
I take two offsets and do not worry about optic square. Doing boundary work locating occupation not always convenient with disto, getting leaning post cl marker.
RADU
Big Al, I think I get your explanation but doubt you get the resolution. I think in terms of what are we trying to accomplish, with that being a location of a point. Pretty simple stuff IMVHO.
I'm a real big "outside the box" thinker, having been solo for 20 or so years. For example, if I'm doing a GPS survey with a couple buildings. Always an issue when you put the rover up close, lets say within 10 or 20 ft, depending on the height of the building. GPS sucks then, and I don't do it.
I do not mess around with offsets or measuring to corners. I take my friendly rover and take a shot at "BLD LINE 1 N". Perhaps 666.66 ft off, who cares. Then I go to "BLD LINE 1 W", maybe 82.666 ft off. Each building has 8 shots, maybe more maybe less, but always on a building line extended - along that extended building line at whatever location suits my needs.
In CAD (or my DC), I just intersect the lines. Bingo, you have a square.....
Within my field notes is the wall to wall measurements to make sure my "square" fits my world. Works for me 100% so far.
Think about it, but make sure you code it right and your field notes are right, or your stupid CAD guy will ruin your day
$0.02
Go Red Wings!!!
Wayne...
How do you get accuracy for an architect or if boundary surveying to locate to 1cm?
RADU
Well, we don't, but if you've got an old bi-pod, surely you could take the thingy that clamps to the pole off, remove the legs and attach it to the pole to give you a "hook".
Most of the time, I find a way to measure from the object as opposed to the object. Keeps me from dumping my pole in the dirt.
I would think that an "optical square" would be a right angle prism.
come on RADU
Building locations to 1 cm? Would that be to the foundation, the siding, the edge of the rock facia, the eaves, door knobs, or the bay window knock outs.
Staking locations within 1 cm, yes. Locating locations within 1 cm, no.
My mistake was introducing a GPS procedure into Al's question for prism rod use. Sorry about that off topic. Hopefully our grasshoper grasps the concept that there are more than one way to skin that cat, was my point. I've worked with those rod offset gizmos before and I think they are just a big PIA, especially with a robot rod (think too heavy). I always have my 25 ft Lufkin on my belt for whenever I need it.
points offset to rod
(there is something utterly broken about replying to messages, I want to reply to the whole thread like on the OLD, OLD board, but always wind up replying to some sub-message somewhere in the middle of the thread)
How I do this in the field is overkill, but it gets a point that is just as accurate as any other point on the job:
1) Move the robot to a place where you can see the point in question,
2) Do a quick 2 point free station to get position and orientation,
3) shoot the point in question with rod & glass OR reflectorless.
If you are using the reflectorless to shoot control that you previously set in vertical surfaces (tack, nail, sticky vinyl target, etc.) you can do this in seconds without any walking. Takes a little longer if you have to walk the rod to a couple control points.
In this way, the point is shot directly, it is in the data collector with every other point, and shot with the same accuracy as every other point ... there is no confusing little exception of, "oh, and we shot that as an offset, was it left or right? did you read the inch side or the tenths side of the tape? Was it really 1.3' North and 2.4' west? Was the tape level?" etc etc etc.
If it's a design as-built for an architect, or a building footing, or occupation being shot for an ALTA, how can you certify that your compass and tape offset shot has the same error ellipse as your total station work?
A disto device is a good idea. I like it.
points offset to rod
half,
Thanks for your explanation. I am not sure I understand what you mean when you write "do a quick 2 point free station". Are you talking about a repetition sequence to a new traverse point, i.e. backsight and foresight forward and dumped? Or, are you talking about doing a resection from two control points? Either way, I suppose its immaterial. You are setting up new control where you can observe the point directly.
Sure, for anything discrete, like a pipe, stone bound, building corner, especially where it is controlling, you want to have a good sound certifiable measurement to that point, and what you describe is entirely satisfactory in that respect.
However, the application I am thinking of does not require such precision, or stated another way, the cost of that precision is unwarranted. Let me explain my situation.
Here's what I'm doing - boundary traverse work around the perimeter of a large wooded lot. Two sides of the lot abut an ancient road, and there are stone walls which exist on each side of each road, which I would like to locate. The stone walls are about 3 or 4 feet wide, and typically a couple of feet high. In places, the wall has deteriorated, or maybe wasn't set as well as other portions. The wall meanders horizontally, and slightly, along its length. In places there might be a horizontal bend in the wall, where the wall changes direction.
It is very wooded. Lines of sight between traverse stations, which typically run about 200-300 feet, must be cleared. Sometimes the inter station traverse length is longer, especially when the traverse runs along the road. However, the stone wall is set about 30 feet off the center of the road, and is typically thickly vegetated. We seek to take shots on the stone wall at intervals of 50 feet or so. Clearing a straight line between the total station and each of the points on the stone wall is terribly difficult and time consuming. Alternatively, setting up station every 50 to 100 feet so that points can be observed without much cutting is also terriby time consuming. The alternative, that I believe is suitable in this case, is to take a "distance offset" shot, with a distance right or left from the prism pole to the point being indirectly measured.
I agree that this introduces the potential for error, but carefully done by experienced personnel, using the data collection software that we have (Survey Pro Robotic 4.8.5), this is a reliable method, good enough for the intended purpose. The most difficult aspect of the process is to measure the offset distance, hence this post.
Others have suggested that measuring from the point in question to the prism pole is preferable, but in this case, that is not practical, as the rocks in the stone walls in these parts are generally not angular enough to hook a tape on. The rocks are rounded, and the tape slips off. In other cases where we are locating the remains of wire fence, it is by contrast doable to hook the end of the tape on the wire, and measure to the prism pole.
I like the idea of a Disto unit, and will be exploring that, as time allows.
Thanks for all the posts (by the way, I agree it is awkward to post in the middle of a thread).
Big Al
> (there is something utterly broken about replying to messages, I want to reply to the whole thread like on the OLD, OLD board, but always wind up replying to some sub-message somewhere in the middle of the thread)
>
> How I do this in the field is overkill, but it gets a point that is just as accurate as any other point on the job:
>
> 1) Move the robot to a place where you can see the point in question,
> 2) Do a quick 2 point free station to get position and orientation,
> 3) shoot the point in question with rod & glass OR reflectorless.
>
> If you are using the reflectorless to shoot control that you previously set in vertical surfaces (tack, nail, sticky vinyl target, etc.) you can do this in seconds without any walking. Takes a little longer if you have to walk the rod to a couple control points.
>
> In this way, the point is shot directly, it is in the data collector with every other point, and shot with the same accuracy as every other point ... there is no confusing little exception of, "oh, and we shot that as an offset, was it left or right? did you read the inch side or the tenths side of the tape? Was it really 1.3' North and 2.4' west? Was the tape level?" etc etc etc.
>
> If it's a design as-built for an architect, or a building footing, or occupation being shot for an ALTA, how can you certify that your compass and tape offset shot has the same error ellipse as your total station work?
points offset to rod
Sounds like a good job to do in late fall, before the snow flies. Not so many of those pesky leaves to get in the way.
But quite frankly Mr Al, I find it difficult to absorb how determining the location of said wall is a problem to any surveyor in any state or country. Just go tie the damn thing in, fer chrissakes. Ain't building a watch - its a delapidated stone wall, so note it as such on the plat.
My guess is it is totally budgetary. Certainly not technical or equipment related by any means. Raise your prices.
Godspeed to your project.
PS - agree with Mr Bubble about the posting order of chaos. Still trying to sort that one out, but it seems if you just hit "reply" under a post, it will just stay there. Go back to the original poster and reply, it will drop to the bottom. I think.
points offset to rod
Al,
yes, it's a "resection" but with EDM distances in addition to angles.
Sounds like you have a lot of foliage, the reflectorless solution might not work if there are just not any clear shots without brushing it out.
Maybe with a really high rod you could see over the foliage to get shots on the front toe, top & back toe?
points offset to rod
Wayne, Don't jump to conclusions. I'm getting paid for this work. I'm just trying to refine my methods. You don't have to get all religious on me about it. 😉
points offset to rod
Yes, there's alot of foliage. Doing it in the fall would be nice, but that's the way it goes. We're taking one shot on the centerline of the wall, not getting too fussy about it. It's location is relevant, even though it is old, but it is still a stone wall, with all of its peculiarities, twists, and deterioration over time.
Sometimes a high rod works, sometimes taking the prism off the pole works, sometimes a low rod, sometimes flipping the prism pole upside down. And then, there are times when there is no hole, and you either cut line or take an offset shot.
points offset to rod
> with all of its peculiarities
Don't know how many topo and/or boundary survey's I've done in my 35 plus years as a surveyor. I do know that they are never the same. Every shot is different and requires special attention. Some are more important than others, for certain. We just need to know when and why each shot is so special.
That is one of the things that makes this job so fun. Enjoy this one Al, it seems like a good one.
If you can keep your traverse lines within 25' of the stone wall and you aren't running elevations in the survey, then I might be inclined to fix a prism to a 25' telescoping level rod, use a Suunto compass to get an azimuth/bearing back to the instrument, add 90 degrees in your head, find the spot on the wall that corresponds, take the shot then extend the rod through the brush to get your distance.:-|
Spencer Tape
Spencer® 35' Logger’s Tape
120" Diameter in inches, 10ths on one side, 35' linear in feet, 10ths, 100ths on the other side. Heavy-duty chrome-clad tape line with claw hook. Heavy-duty plastic case. Fast automatic rewind. Durable belt clip. Case dimensions: 4-1/4" x 3/4".
They come in (I think) 60' & maybe 100' also)
You'd have to walk to your stone wall. Perhaps you could measure to a point here there's a crack or gap in the rocks. I used to attach a nail to the end to stick in the ground, log, tree whatever. Go back to where you can see, take the shot, give the tape a pull and it comes home.
DJJ
Spencer Tape
Thanks, Doug. I think that's an excellent suggestion also. Particularly the part about how you use the nail in the end of the tape. I like that.