What is this thing mounted on a San Francisco building?

We are having fun in the G+ Boing Boing community. Our friend Rob Walker posted this photo and said:

I was in San Francisco recently and walking from Market/8th to the SF CalTrain station I kept noticing these odd little things, mounted about 10 feet off street level, a few-inches-wide tire-like object often (but not always) accompanied by small target symbols. What is it, is it functional, or some sort of street art thing. Anybody know?

What is this thing mounted on a San Francisco building?


      1. I see these around central London too. They’re in place to ensure the buildings are not undermined by the work being done on the new Crossrail railway line.

  1. I believe that’s an anchor for formerly pole-carried utilities, now under-gounded. I don’t recognize the “target,” but my bet is that they are patches over the former holes where the lines, from the anchor, entered the building (and they merely look like targets).

    1. Yea, there are two paper targets which are useful for most surveying but are not as high precision as some operations require.  The larger red looking one is a survey prism which is typically used when the accuracy/precision demands of an operation are high or you are gathering lots of data over a long period of time.

      1. Those adhesive targets are likely plastic, not paper.  The bottom one appears to be Trimble brand (based on the crosshair design.)

        The need for a prism for accurate EDM is outdated, my LiDAR scanner can get sub 3mm accuracy w/o a reflective target, and my total station can do darn near 1mm ranging on anything – prism or paper.  The only reason to use a prism with modern equipment is if you’re going fully robotic target acquisition. Though they may be using the “red” target simply for off-axis aquisition. Those flat targets are only really appropriate for use when your line of sight is perpendicular to them – use them from a side angle and the width of your EDM’s spot becomes a factor as you’ll get returns from multiple distances.

        EDIT: Though I swear I can see the word “Leica” on the top targer. Odd in that Leica and Trimble equipment are rarely seen to mix in the wild.

  2. I’m pretty sure that’s one of those things the aliens put on our buildings to help them scale the walls. The targets are actually reminders that there was no intelligent life found within.

    1.  It’s a beautiful and entertaining read, but being a contractor used to working under the table, none of those examples looked like anomalies to me. And the “node” in the comic that looks like the picture above is certainly a piece of leftover knob-and-tube wiring. More specifically, the knob.

  3. looks like a retro reflector to me … probably for statistics getting of land movment … look directly across it for some sort of laser box 

    1. Almost right!  The laser box will be a surveyor’s transit (or “total station”).  So it won’t be operating continuously.  More likely they’ll just show up every week or so and take a single measurement.  What you can look for, if you’re that interested, is reference points drawn on the sidewalk, or nails driven into the street, and labeled in spray paint with some kind of number.  These will be their reference points for where they will set up  their tripods.

  4. If it were Charleston, I’d say earthquake bolt. Being San Francisco, I’m betting something to do with weed or condoms.

  5. As per the Hotel Utah in the background, this appears to be on 4th street where the new central subway line in being built. I wouldn’t be surprised if they are concerned about buildings moving as they dig the new tunnels. 

    1. I would nearly guarantee that’s spot on.  I have personally put these things up on buildings near new condo developments in a city where earthquakes are pretty much completely unheard of.  

    2.  This is my guess; I’ve spotted dozens of these on older buildings in Singapore near excavation work for new MRT (underground railway) lines. Presumably getting early information about subsidence – and/or confirmation of it not happening – are pretty important when tunnelling near/under old buildings.

  6. It’s infra-red magnifying glass death-ray for Bullet Ants. Bullet Ants are naturally drawn to a bulls-eye target, and once centered the magnifying glass cooks their asses (while giggling in a particularly childish manner!)

  7. Ground based gaydar installations.  San Francisco uses theirs with the polarity reversed, to detect straights.

  8. I know they use the same tech on buildings that they’re afraid are moving/might move. The guy mentioning the tunneling nearby probably nailed the answer.

  9. May be an ancor for the overheadline of a former street car line? You find tons of those on old buildings here in Frankfurt. They look different thou.

  10. Those are most indeed survey targets.  I know because I’ve had to install survey targets myself, and for the purpose of detecting building movement.  I do not however live in San Francisco, the city I live in is well out of an earthquake zone.

    At 10 feet those are for a lower reference point. Look very carefully way up on the building, they should have installed a second set at the 7th-ish floor or so.

    Look around the area.  Are there any new developments within a block or so? If so, if anybody is driving piles or shoring beams, then a monitoring program of the surrounding area will be warranted.  Even small shifts if the soil can mean big issues, especially in buildings that old. 

    Of course this is San Francisco you’re talking about, it could be for fault movement, but just to say, these kind of monitors are hardly restricted to that kind of program.    

    [Edit- Above poster mentioned a new subway tunnel is being dug in the area, I can nearly guarantee that’s exactly what it is, and that said tunnel contractor received the invoice for the installation and monitoring of these things via laser total station]

  11. It’s a nose ring (using Feng-shui, that’s where the building’s nose is).  The markings are tattoos.

  12. All the buildings in that area are basically floating on mud.  Monitoring movement is fairly common.  

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