Since I've begun learning the art and craft of surveying, I've spend a great deal of time identifying the sources, and quantifying the magnitude of various errors that can creep into the process.
My recent obsession with elevation errors, which led to a "simple" triangular traverse, resulted in a renewed interest in paying attention to "measure ups", using great care in measuring HI's and HR's.
Quite by accident, I was going over my tribrachs, prism poles, etc., and I noticed this:
See the "4.11"? Never noticed it before. Guess what? The pole is not read in feet and tenths, as I have been doing since I bought it! Who'd guess that 5.4 meant 5'-4"? Not this Grasshopper, apparently. I've calculated that, depending on the distribution of the setup heights, generally between 5.0' and 6.0', that I've been introducing an error averaging .092' into my traverses, reading and recording tenths rather than inches!
I often use the prism pole and tripod for initial back sights (working solo), so that I can free my tripods/tribrachs for traverse points, so it means that if off by .093' on the initial back sight, this will propagate throughout the traverse! Almost a TENTH!
Argh!:-$:-$:-$:-$
Well!!! I don't know if I would have noticed that myself! Can't recall ever seeing a prism pole in inches before. 1/4 inch graduations at that. You traverses will never be the same. 😀
rfc, post: 337143, member: 8882 wrote:
See the "4.11"?
That's a dangerous tool. Seems like maybe something one may leave laying around for a competitor to grab . . . . (Not that i would ever do such a thing...).
Jules J., post: 337169, member: 444 wrote: Well!!! I don't know if I would have noticed that myself! Can't recall ever seeing a prism pole in inches before. 1/4 inch graduations at that. You traverses will never be the same. 😀
I think it's because I bought it from a concrete contractor. Do construction folks use feet and inches as a general rule? I'm thinking of scribing or etching it in tenths. I don't need another "conversion" task to be thinking about.
[sarcasm]Some clerk shipped you an architect pole[/sarcasm]
RFC,
I suggest you check the height of the rod, prior to beginning your field work for the day. Hook an engineer's hand tape on on the rod tip and measure up. You will be measuring the hypotenuse and if you have a 0.3' offset to the center of the mirror, you would subtract 0.01 at 5 foot height. The rod height is adjustable for different mirrors and will adjust during the course of a survey if you are not careful or something else can go wrong.
The conversion is easy and you should be able to do it in your head once you realize the .25' = 3" and you have to go to the nearest 3" increment to subtract or add since 0.125' = inch and a half. With that in mind, 1/8" is equal to 0.01' until you get an inch and a half or in other words 1 3/8" or 11 - 1/8" increments =0.11'.
Best,
Larry
I never use the numbers on the rod. We always measure.
rfc, post: 337178, member: 8882 wrote: I think it's because I bought it from a concrete contractor. Do construction folks use feet and inches as a general rule? I'm thinking of scribing or etching it in tenths. I don't need another "conversion" task to be thinking about.
I worked in a power house last year where the stops for the elevator were marked as the elevation for the floors. And they were all marked in feet and inches. I almost took out my marker and added the decimal to the numbers.
Andy
Tommy Young, post: 337195, member: 703 wrote: I never use the numbers on the rod. We always measure.
I've never even thought of doing it, numbers on the rod are just approximations as far as I'm concerned. Occasionally I will use them to measure something when I didn't have a tape with me for some reason.:-S
You do get used to each rod, they are all so different, the one I use most is 0.12' low for my GPS measure, different for a total station prism, and different for all the robot glass.
I wonder whether that threaded portion is always screwed in the same amount - another small variable.
Bill93, post: 337266, member: 87 wrote: I wonder whether that threaded portion is always screwed in the same amount - another small variable.
No. I've adjusted that very carefully, lol. I set the pole at "5", and measured up to the centerline of the prism target. At 5'-0" (5.0'), it's dead on!:-D
rfc, post: 337178, member: 8882 wrote: Do construction folks use feet and inches as a general rule?
The only professions that still use inches:
- Carpenters
- Architects
- Hookers
B-)
I would probably just get rid of that rod and buy another.
I don't like the adjustable prism setup either.
I had marked some cuts for a drainage swale and the contractor called me up completely confused. I ended up meeting him on the site to explain to him what tenths and hundredths are. He was fairly confused still and asked if I could remark all of the lath in feet and inches. I said no. He asked why not. I explained that decimal feet was the industry standard and it also reflected what was on the plan set. He then asked if there was a good way to convert between the two. I showed him my 12' pocket tape that was marked in decimal feet on one side and inches on the other. I told him that he could buy one of those at any good supply center. Then I smiled, told him to have a nice day, and left.
skwyd, post: 337350, member: 6874 wrote: I had marked some cuts for a drainage swale and the contractor called me up completely confused. I ended up meeting him on the site to explain to him what tenths and hundredths are. He was fairly confused still and asked if I could remark all of the lath in feet and inches. I said no. He asked why not. I explained that decimal feet was the industry standard and it also reflected what was on the plan set. He then asked if there was a good way to convert between the two. I showed him my 12' pocket tape that was marked in decimal feet on one side and inches on the other. I told him that he could buy one of those at any good supply center. Then I smiled, told him to have a nice day, and left.
Big inches or little inches?
12 inches to the foot or 10 inches to the foot?
Long time ago I got paired up with an engineering intern who was about the most conceited and obnoxious individual I've ever had the displeasure of working with. His daddy was an engineer and his superiority complex was over the top. First day out all my vertical backsight checks were consistently off 2-3 tenths. The little twerp asked me if I knew what I was doing. Told him up until now I thought I had. After another couple rounds of this I finally asked him to show me the hand tape he'd been taking all his measure ups with. Yep. You guessed it. Carpenters tape. He'd been reading me measure ups in feet and inches and calling them tenths over the radio. Asked him if he wanted his tape back and when he reached for it, I threw it as long and far as my arm and gravity would allow. Told the boss on returning to the office that if they sent him out with me again, I was going to bury him in a shallow unmarked grave.
Just because I'm paranoid, doesn't mean they aren't out to get me.
get rid of the rod, It will haunt you some day and you will lose more time and money then the cost of an new rod. also always measure your rod height don't rely on the marks on the rod. I always liked to use the peanut prism the height never matches the pole.
It's not difficult to make a spacer that is mounted to the base of the peanut prism that boots the prism to the correct height so that you can have more hours in the day to do better things than measuring your rod height with a pocket tape every time you need to raise/lower it.
Somebody with a lathe could easily make the correct part.
MightyMoe, post: 337352, member: 700 wrote: 12 inches to the foot or 10 inches to the foot?
Ask Steven Tyler...
[MEDIA=youtube]hyd7gNqLI5k[/MEDIA]
imaudigger, post: 337438, member: 7286 wrote: It's not difficult to make a spacer that is mounted to the base of the peanut prism that boots the prism to the correct height so that you can have more hours in the day to do better things than measuring your rod height with a pocket tape every time you need to raise/lower it.
Or you can set it to an even foot and note the height on the rod