Reflector tape backsights

Paul Goebel · Post by **Paul Goebel** » Thu Jan 15, 2009 3:29 pm

I am thinking about setting permanent "reflector" backsights at a site that I will return to many times. In particular, I am looking at Rothbucher reflective tapes that I saw in a Professional Surveyor magazine story recently.

I am concerned about having different prism constants on the project, and just how much tolerance these targets have from being shot straight on. Does anybody have experience with these?

Stan_K · Post by **Stan_K** » Thu Jan 15, 2009 4:24 pm

Paul,

I've used many different brands of reflector tape with good results. The biggest difference was the usable distance - a direct result of the quality of the reflective material. All have a prism constant of 0 (zero).

Shooting the target at an angle MIGHT induce a distance error - this is caused by the actual size of the edm laser beam.

You will need an X,Y,Z coordinate on the reflector tape, therefore you need to use the correct prism contant. Yes, I know some data collectors are easier to switch than others - Sorry.

Use good adhesive! Reflector tape has saved our rear-ends many times on construction sites. Set them off-site or where generally not visible to the construction crews. If they can't see them, they can't move them!

Ian Wilson · Post by **Ian Wilson** » Thu Jan 15, 2009 4:40 pm

Bicycle reflectors expoxied on to bridge abutments, etc. make great “permanent backsights”, too

You can even get fancy and use the white ones and paint a pair of opposing quadrant on the face of the reflector with transparent candy apple red model paint to give yourself a nice aiming target.

Stick with one style and brand of reflectors and check to prism offset constant against a prism of know offset before you stick one up somewhere. The offset will be a function of the thickness of the reflector layer.

Paul Goebel · Post by **Paul Goebel** » Thu Jan 15, 2009 4:54 pm

I hadnâ€™t thought about the bicycle reflectors in a while. My data collector is one that wonâ€™t accept more that one prism constant at one time, so changing that would be a minor inconvenience. One of the backsight positions on my project would need to be shot from many different angles, so a 360Â° prism would be ideal if I could afford it.

Scott · Post by **Scott** » Fri Jan 16, 2009 11:14 am

If you glue the reflector and then locate it from a few different control points and put those locations in any adjustment you do to the site, prism constant should not be a factor because you are just flat out locating the refelctor itself and any inherent prism factor wherever it is shooting to. You don't need to know exactly where the wall is (which is what the prism constant would give you) that the reflector is attached to. Does that make any sense?

Paul Goebel · Post by **Paul Goebel** » Fri Jan 16, 2009 11:54 am

Yes, that does make sense. I don't care where the wall surface really is. The distance to these points is only used as a check for blunders anyway. sighting a point for a horizontal angle is the main purpose for the marks.

Scott · Post by **Scott** » Fri Jan 16, 2009 12:20 pm

Then all you need is a line drawn on the wall and no reflector. Go reflectorless and still use the black line.

D Ryan · Post by **D Ryan** » Fri Jan 16, 2009 1:07 pm

The reflectors add the option of doing a "re-section" if you lose control. Will work for both vertical and horizontal. We have a few gravel bars where we lose our convenient control every year. One of those sites has a railroad bridge that goes right by the site we have some RP's on that we use for pulling the control back in. l've always thought that site would be ideal for a few pieces of reflector tape for "re-sections".

Our reflectorless gun automatically goes to zero prism offset when in refelectorless mode, so that takes the data collector out of the equation. Of course you have remember to punch the hot key on the total station to set it back to 30 or your next series of shots are screwed (well, by .09' if it matters...).

Dave Ryan
Humboldt County

Paul Goebel · Post by **Paul Goebel** » Mon Jan 19, 2009 8:17 am

I was pointed out to me that the proper prism constant needs to be used. Not adding the constant will cause position errors if the reflector is shot from different angles. If you were able to repeat the exact same setup each time, this would not matter.

goodgps · Post by **goodgps** » Tue Feb 03, 2009 9:00 pm

We put reflector tape on rain boots to do topo in wooded areas where the inst man (person) can only see below the leafy area. it works pretty well.
"boot men" clobber around in the forest Less chopping and destroying of vegitation. "p"architects really love this method, because it saves their wooded areas.

signed
"Woody Slopes"

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