How to shoot building corners

Once you switch to reflectorless this will no longer be an issue, but I used to hold the rod as close to the corner, shoot the distance, hold it and turn the correct horizontal angle to the actual corner and record that , this way the building would square up a lot better.

Some data collectors may not have that function though.

It depends. If setbacks are critical, then tighten it up, otherwise I usually just shoot it on a 1' offset (my boot length) on a building line extend, which goes into the description. Or just hold the prism as close as I can. Depends on the job.

GPS locations get tricky. All I do now is shoot the building line extended in each direction and I don't care about the offset - it could be 15' or it could be 40'. Sometimes I'll extend the line in the same direction at say 15' & 30' +/-. Whatever is convenient. It's still the same line. It takes 2 shots for each corner. I describe them as BL S, BL E, BL W. Sometimes for major jogs you have to add a number, with BL N1 being exterior, and BL N2 being a jog, parallel with BL N1. Then just connect the dots, intersect the lines, and thus your basic building footprint. Much faster than measuring an offset, which better be at least 10', depending on building height. Jogs & wierd stuff you have to get more creative.

Your data collector should have an offset program that allows you to shoot a separate angle and distance to the corner. It is best to use a rod with a mini-prism. Carefully position the rod so that the prism is the same distance away from the gun as the building corner, making sure that the prism is as close to perpendicular from the instrument man's line-of-sight as possible. Read a separate angle to the corner, and store the shot. This is the way I've always done it, and it is the most accurate way I've found. I also shoot every building corner I can see, not just two or three. You need to do this to get an accurate topo anyway, including ground shots at inside corners.

Personally, I've had terrible luck shooting buildings reflectorlessly. It is nearly impossible to get an accurate shot on a building corner reflectorlessly. You need to take at least two, and preferably more, shots on each plane of the building, then intersect the planes to get a good position. I've found reflectorless shots to have hit-or-miss precision. Besides that, reflectorless shots have bogus elevations, which need to be filtered out of the topo, further complicating things.

On a final note, shooting approximate building corners by getting "close" with the rod is a big no-no IMO. Especially when doing a topo. I don't want my measurements to property lines or setbacks to be approximate. Your topo is the basis for design, perhaps for a building addition. An architect who gets your CAD file may very well rely on your building measurements for design. I'd give him or her the most accurate building positions I possibly can.

(Note: Sorry, this reply was meant for the OP.)

Reflectorless with a Leica TCRA 1103+

We do a lot of work for architects and try to hit our points really close. We do an offset shot, as noted above, with a mini prism. You get a lot better shots with the mini prism than doing a big offset with a full size prism and target.

Use a little piece of reflective tape if you don't have DR. Don't forget to change the prism offset!

http://www.ebay.com/itm/1-Roll-Silver-Reflective-Tape-2-in-X-30-ft-/220691496961?pt=LH_...

Get a roll of this stuff and cut it up into ½” squares and carry them in your pocket in an old pill bottle and they will prove invaluable. Not only for surfaces that are not reflectorless friendly but for building corners that are in difficult positions (opposite face with back ground interference). I also use these reflectors for control points and offsets to monuments. The precision is very good … in fact if I’m off more than 0.01’ (x,y,z) I know something’s amiss.

i usually use the prism offset method
i have also used the 3-point on a plane and turn to the corner with the reflectorless - tds function

i have had great luck with the GPS with 2 methods:

- setup in a random point with the bipod & measure to several corners while I let the RTK cook down to 0.01' average. do this 4 or 5 times around a building and you have the redundancy necessary to average out the errors.

- i quickly located some shacks on the beach for free. these were non-critical and not for building, planning or other use (we'll just say it was for GIS) i held the GPS and lined myself off each corner of the building and tried my best to be in line with the face. out on the beach, it was easy to get the solutions and to get to the lineouts. in the computer, i connected all the points, then took an approximate average of a couple of the lines, held 90s and squared up the buildings. i did return for two shacks and measured them, my method came out within a tenth or so - of course, i cannot imagine any of the shacks are square, therein lies your next conundrum.

so, do you hold the measurements around the building, or the points or a combination. i worked on a property line in RI where the line became a curve. the building was right on the lot line and had bowed out over time (like 200 years of time) and the neighbors made a boundary agreement to hold 1' off the building. we shot it a few dozen times with reflectorless and held a best fit solution of those points to create an arc to offset. They gained a foot in the middle.

Few people here don't do that many corners. Reflectorless is the best way, but it's not the most efficient way and can be inaccurate for corners facing away from you.

I've measured the diameter of my 360d prism (90mm).

Then I put in an appropriate offset either left/right or front/back.

I typically will get on the roof, take my light sabre and cut a hole in the overhang and actually occupy the building corner. Resect in to as many control points as I can see, which here on Tatooine is usually quite a few if not all. Of course I will always stake out another one, repeat the process and do a quick tape check on the diagonals just as a double check. Sometimes though, when I have time constraints I will just use the force, unless my lazy arsed Instrument Droid forgets to load it in the X-Wing. In that case I just call upon my mentor ObiHughPackardi, sometimes he's my only hope. 😐

I use a mini prism with a 0 offset, same offset as the multi-prism.
In order to make the topo work, I use an "XX" after the description code on any shots I take with the mini prism so as not to have a spike or hole in the DTM. The "XX" shots are easily ignored or removed from the data for the DTMr.

So a building corner would have two shots:
"GND" taken with the rod on the ground at the corner for dirt elevation
"BCXX" taken with the mini prism at a random height on the actual building corner

For most of my topo work I need elevations on my building corners, so no reflectorless. I use the offset program in my DC. Quick, easy and accurate, both for turning angle onto the corner and for adding the distance offset on interior corners.

I also tape the buildings and plot the footprint using the taped distances. This gives cleaner linework and is a redundant check on the building location, usually critical to design work.

Rick

It depends on how accurate the shot needs to be.

Often a tenth or two makes no difference (a mountain top radio vault, for example, miles from anything) so I just have the rodman get as close as possible.

If it is critical then I do either horizontal offset or reflectorless.

If elevations matter then have the rodman hold the rod at the corner, set the vertical angle, have the rod get out of the way then aim and shoot reflectorless. Or if you are by yourself you can go around with keel and mark up 5' or sometimes I measure up to some definite horizontal feature on the building that can be aimed to vertically.

With very few exceptions, horizontal angle offset or online distance offset, depending on circumstances.

> I typically will get on the roof, take my light sabre and cut a hole in the overhang and actually occupy the building corner. Resect in to as many control points as I can see, which here on Tatooine is usually quite a few if not all. Of course I will always stake out another one, repeat the process and do a quick tape check on the diagonals just as a double check. Sometimes though, when I have time constraints I will just use the force, unless my lazy arsed Instrument Droid forgets to load it in the X-Wing. In that case I just call upon my mentor ObiHughPackardi, sometimes he's my only hope. 😐

Some other forums I visit have a special area to archive "Hall of Fame" posts. This is one that should be saved for posterity.

I set spikes at a 1' offset along the foundation, at least two on each side, sometimes 3, then locate the O/S's and calculate the corners in the office. If it is not real important to be that precise I use the prism and right angle O/S routine in the (TDS) data collector. This is with a robot, if I have a helper then the distance/angle O/S routine works well.

T.W.

Doing It Right, Depends On The Equipment

In the past when using a Topcon 301, with wide beam spread and a 3" prism, one could aim at the corner and get a solid distace from the prism 2" to the side. Using a newer reflectorless the beam spreads are narrower. Still one can aim at the corner and get a solid distance from a mini prism to the side. Other times it is neccessary to use the SDA routine.

I help another surveyor out from time to time with topos. His preference is to locate the building corners with elevations off, then take his topo shots near the corners. If he does take an elevation shot on a building corner he holds the rod to the corner then sets his mini prism at the rod height.

As to the reflectorless shots, on my first project (10 yers ago) with the reflectorless I took a building corner shot, but when it came time to connect the dots I could not find that corner. Turns out my setup was in line with the building and the distance I got was not to the front corner, but a return from the aluminum siding trim piece to the rear. That shot was 0.02' from the rear corner I had shot with a rod from a different setup. OK, I had enough corners to square up the building and was not topoing. If I topo reflectorless it is to locate buildings and features that are offsite far enough that +/- a foot is close enough. I guesstimate a rod height based on windows etc. Less of a problem today because now I use a lot of LIDAR.

If I need a reflectorless corner now my procedure to to aim to one side, then use the distance button on the EDM and walk in to the corner and past it. Sometimes the mim/max distance is not exactly at the corner, since one needs enough surface to reflect and I may then use the SDA feature on the data collector.

For GPS topo, the best elevation comes from a diagonal offset from the corner to get a minimum 3/4 sky view. Corners are best done by offsetting a greater distance on the building line. Since one wants greater precision on building corners than topo shots, 8'-10' minimum both ways, a hand held laser being a time saver.

Paul in PA

Depends on the accuracy needed. Typically reflectorless, or using an offset is most accurate. I'll set prism at a 90, shoot distance then turn to corner. If location is just needed for basic location shooting the prism is fine, without turning to the corner.

If you just need a general idea where the building sits in relationship with the property, then holding the rod as close to the corner as you can is ok.

You may want to consider the roof line as it is part of the building too and it may stick out farther than the face of the building.

What I do to locate the corners exactly is to use a framing square to set a nail a foot or so off the building corners and then shoot those points and then measure the roof overhang.

Of course in my line of work, I always have to go inside the building and asbuilt column lines too so that information can be added to the drawings and then used for either building expansion or placing new equipment...etc