Well this one may be so simple I'm overthinking it big time. Or, there may be more than one way to do what's needed.
Doing some "micro-topography" in and around a building...mainly related to water run-off. I'm not within sight of any of the points in my control network, but don't really think I need to be. It's completely local to the building itself.
What I'd like to do is just set up at a convenient location within sight of all I wish to observe, shoot two corners of the building, and then a ton of other points, from which to do the topo.
Resection calls for identifying two known points to resect from. So my first thought was to do a resection on the two corners of the building. But they aren't points until I store them. So would resection just be not the way to do it? Is there even any way to do a resection if you have no points created yet?
For Store Points, I need an Occupied Point and Back Sight point. So do I just call the point I'm on arbitrarily (5000,5000,1000 or whatever), shoot one corner of the building as the back sight point, set the azimuth to the back sight zero, then store the other corner of the building and carry on from there with the topo? Everything would be in the proper relative position, wouldn't it?
What's the proper way to do this?
rfc, post: 363493, member: 8882 wrote: Well this one may be so simple I'm overthinking it big time. Or, there may be more than one way to do what's needed.
Doing some "micro-topography" in and around a building...mainly related to water run-off. I'm not within sight of any of the points in my control network, but don't really think I need to be. It's completely local to the building itself.
What I'd like to do is just set up at a convenient location within sight of all I wish to observe, shoot two corners of the building, and then a ton of other points, from which to do the topo.
Resection calls for identifying two known points to resect from. So my first thought was to do a resection on the two corners of the building. But they aren't points until I store them. So would resection just be not the way to do it? Is there even any way to do a resection if you have no points created yet?
For Store Points, I need an Occupied Point and Back Sight point. So do I just call the point I'm on arbitrarily (5000,5000,1000 or whatever), shoot one corner of the building as the back sight point, set the azimuth to the back sight zero, then store the other corner of the building and carry on from there with the topo? Everything would be in the proper relative position, wouldn't it?
What's the proper way to do this?
I would go with the arbitrary setup, unless you can pick the building out on google earth and assign some rough coordinates to it to resect by.
I set thumb tacks in PP and wooden objects to use for resection to gather info in those little areas confined behind fences and hedges and such.
Tack and tab of flag works too.
0.02
Your approach sounds okay. But orientation can help but then if adopt Adams idea clearly state your bearing datum. It's still an 'assumed datum.
I'd also read a reference bearing(s) to some prominent high feature.
One never knows when you might be back to extend or survey nearby, so accurate ties to permanent features (buildings, bolts on railings, drill holes or nails in kerbs) are worth the effort.
And make sure your references are 3D.
Could you possibly see the 2 building corners from your control network? That way you could assign coordinates from your control and then resection on the same where you could setup and start topography (disposable sticky targets work great for this).... Or set a couple of random points with GPS based on your control and go.....once you have something to work off of in the area you should be good to go
doogle1973, post: 363557, member: 1552 wrote: Could you possibly see the 2 building corners from your control network? That way you could assign coordinates from your control and then resection on the same where you could setup and start topography (disposable sticky targets work great for this).... Or set a couple of random points with GPS based on your control and go.....once you have something to work off of in the area you should be good to go
Nope; too far away. I'll get there this summer with the control network, but didn't want to wait to get this done. Don't have GPS, and as I said, I really don't care about orientation; I was really just questioning the proper way to use SurvCE when you start such a project in the middle of nowhere.
I think the answer is forget about resection...just set up where everything is visible (mark the spot if I want to go back), and start shooting. I can put a prism close to the corners of the building; my wife would have a fit if she started finding reflectors stapled to her hand built log home. :pissed:
Resection can only occur on points that are already in the system. When I do a resection (actually 2 point free station) I still shoot and keep additional points to the originals. One is as a permanent check and 2 is to possibly adjust in he future.
I am having trouble understanding how you can do topography if you do not have existing points with elevations from which to start.
BTW, a log cabin is the hardest building to get good corner shots on. Were I to need to relocate my log cabin corners in the future I would have no problems in stapling targets to the logs. Once removed the staple holes will be invisible to normal observation in the rugged look of the logs.
Paul in PA
RFC I'm not sure what your purpose is for this survey, but following your threads you seem genuinely keen to pursue correctness in attaining your goals.
My following comments are in no way whatsoever even intended as an admonition so please just take them as an old surveying sage relaying life's survey experiences.
Pretty sure its been said here but how you begin is probably how you continue.
I'm not sure what your comment re not interested in orientation is about, but as a surveyor its hard to ignore, and its not very professional sounding, coming from a surveyor, to say to an enquirer "I haven't a clue which way its oriented". You'd probably get wiped out in the first assessment.
If you start with knowing some orientation, at least a simple north direction, then you can indicate that and put potentially interested parties at ease and not leave them wondering if this bloke knows anything about surveying.
Picking up skills as you go is commendable and you've asked a lot and gained a lot.
Anyway back to the question. You're spot on re surveying with CE.
Regards reading out to other objects, for an added exercise you could observe some key features (RO's) from your known points and calculate intersections and if done from 3 (or more) different setups and with good geometry realise an appreciation of accuracies of well observed angles (to RO's) and measured base line distances.
Its always rewarding to observe such and see good results.
If they're a long way off then be ready for some obvious length differences as a 2-5" 'error' over a long observation does impact the intersected point.
But 2-5" is negligible for on site work which is proportionally much closer to your job than the RO's.
If you get some good results then you could start resecting from those and check the results by other methods.
Surveying never is a one way methodology. Results are what counts.
Keep up the work and don't refrain from asking those questions. It also makes us question or think about our own methods etc.
I agree with Paul about needing reflectors on the corners, or some other repeatable points, and having more than two so there is a check if you come back. Do put a marker at your setup point. It could be an interesting exercise to see how repeatable your positions are.
A compass direction between two points, call it "plan north." should be sufficient for now, and you can tie into other control later by keeping your angles. Having some approximate alignment is beneficial for reducing confusion about what points are what as you work.
I don't see why you can't put a nail in an inconspicuous spot on the building or a tree root and call it 100 elevation, with another one somewhere you can use for a check.
Just add a point at like 5000,5000 and set on that and back sight a random direction. Then just start shooting. Put another temporary point in as well somewhere early just incase the instrument goes off level and you want to reset.
Then shoot your shots. Including the building.
I do this a lot even when I have known points already. Just easier and faster and I can align the points later on the computer... unless I need to be in a system while I'm in the field, then I actually use the resection function.
It really doesn't matter in the least how you go about it since you're not tying to control. The gain of resection off 2 building corners is you cut out the simple step of rotating your topo work to the building itself (which, if you really want to get down to it means nothing since it's not oriented to anything anyway if you haven't tied it to your control; best case is orienting to a photo.....). The other choice of shooting the building and doing your topo woirk leaves you having to rotate to the building, BUT it saves the time of the resection itself.
I would favor the latter choice because you're not gaining anything by resecting off points that don't exist to begin with so in essence you HAVE to do the latter in order to do the former......
Thanks all for the comments. The original question was both general (best practices regardless of software), and specific (SurvCE). I know I can orient the survey, via a solar or two, and probably will. The building is also visible on GE, so I can do that too, as Adam points out. Probably the best though will be to mark wherever I set up, and then when my Control "comes to town", just tie into that point. Easy enough then to translate and rotate in CAD to other control points. I'll have elevation data at that point too.
As for the corners of the building, I don't think I'd need to attach anything to the structure itself (keeping marital strife to a minimum); the foundation corners are visible and I've learned how to do offset shots, so that shouldn't be a problem with a prism pole and tripod. I didn't initially make that part clear.
Regarding Paul in PA's comment on resection, that confirms what I thought. Regarding not having absolute elevation data, I may not have made clear that the purpose of the survey is drainage topo relative to the building. The absolute elevation could be 2', 200' or 2000'; It doesn't matter. My topo drawing is only going to be perhaps 2500 square feet and all the points would be relative to the building only. All water cares about is gravity anyway.:-)
It sounds like you've got a plan.
Be sure to set at least 2 local control points and benchmarks when you do this, in case you need to come back, or you eventually need to tie these into your other control.
If there are trees nearby, I like to use BenchTies for this ( http://www.chrisnik.com/benchtie.html ) - they act as a control point AND a benchmark. If you find you need additional topo, you can set up at a convenient spot and do a 3d resection (there's your resection!) to establish your instrument location and elevation. I find the Benchties are easy to find and very durable (as long as no one cuts down the tree).
I once had a rough path layout that needed to be within 2'. I used an aerial location of a building and resected to several corners by angle only. I came within 0.2'.
just backsight an arbitrary azimuth and do a remote bench off of the building finished floor and start shootin
