Night Shot

That is a long trip, but let's face it, you won't sleep well until you do.

I hope everything works out okay. I agree with Bruce, you won't be able to sleep well until you check the points.

This is what separates the men from the boys, taking responsibility, and making sure things are right.

how far away was it?
+o(

Instrument cooling as the sunset down would be my guess.

Agree with the no good sleep comment. Been there, haven't been able to do that. It'll gnaw on yer innards.

> Instrument cooling as the sunset down would be my guess.

I agree with that statement. I have had the same issue at sunset several times in the past. I learned to check in more often as the sun gets low.

James

What kind of robot?

Same backsight all day?

Backsight - prism on a tripod?

Did you check the bubbles on the instrument and backsight before packing up? In reasonable adjustment?

Did a leg slip?

Did someone kick either tripod?

An inadvertent change to the prism constant? I doubt it, as that would affect distance, not left and right.

How did you calculate the .15? Do you take and record separate shots on the backsight prism hourly as you do the work? Or, do you do check shots? If I'm not mistaken, the check backsight routine (in, Survey Pro, at least) reports angular difference, and distance difference. Did you calculate the .15 from these values? Any chance your calculation was in error?

GOOD LUCK!

> ..there was a security flood light about 3 oclock from the gun to the prism. It was aimed towards the gun and bright. I am thinking it interferred. Anyway I am going back 160 miles to check it Monday. ....

Score one for the active target on the Trimble 5600's.

Went back yesterday and it affected the last 10 shots or so. The set up was good, backsight was on bi-pod. I use the stake to a point routine to check my backsight, one time before I used the backsight check and it thru an azimith in there and I collected a series of bad angle shots. I thought the cooling down theory was wrong because it really didnt cool down much, but these bad shots were right as it was getting dark so it could be true. The backsight was about 400' and the points were at about 250' so the error was around 7 hundredths. The instrument is my trusty leica 1203, the best instrument I have ever owned.

[sarcasm]isn't it great playing detective and figure out where in the he{{ you messed up. [/sarcasm] Been there lots of times. Best thing is you are being concerned about the quality of your work. Seen lots of guys just shrug their shoulders and call it good. Please follow up with what you find. Great lesson for all of us.

Good to know a little more about your setup. I agree with Scotland - good that you are concerned about this, and taking the time to figure it out and fix it. That's the key.

If I were in your shoes, though, I would invest in a tripod to put the backsight prism on. You're betting against yourself, in this case, that the bi-pod remained steady for your 12 hour session. Possible, but I wouldn't trust it (at least, in the future). Wind, rain, people, machines, etc. all have a habit of moving a backsight prism.

Also, my experience has been that the bubble on a prism pole is prone to falling out of adjustment. While there are a variety of field methods that might (and, in a case such as you describe, should) be used to check the bullseye bubble, I think it would be preferable to use a rotating tribrach adapter like the one in the picture below. Finally, I have observed with prism poles manufactured by Sokkia and SECO and others (I'm not picking on these manufacturers but haven't used others), that they are manufactured with rather "sloppy" tolerances, eccentricities about the vertical axis. Given that prism poles are used in the field, get banged up, etc. I think it is reasonable that these manufacturers have relatively sloppy tolerances. Pairing a prism pole, bipod and prism, with a first order robotic instrument, is like painting a house with a toothbrush. I wouldn't trust a bullseye bubble for much better than 0.02', whereas with a rotating tribrach adapter such as below, I think you'll consistently be able to get within .005'. But, neither of these is the 0.15' you initially described.

I would also, if possible, try to get the backsight closer to you. 400 feet is quite a distance. I don't know the constraints of your site, and it might not be possible, but I think you'll get a better reflected signal, and also perhaps better angle measurements, from a prism that is closer to you. I assume that you are using the auto-pointing feature of your Leica, and not manually pointing? Have you run through all the adjustment routines with the instrument to make sure that your pointing is lined up? Do you get a different result if you double your angles to a point, compared with single face measurement?

>I wouldn't trust a bullseye bubble for much better than 0.02'

Depends on the bubble. Most prism poles are fitted with 40-minute bubbles, and they're great if all you do is topo -- it's easy to center the bubble and keep it there. However, they're too course for boundary or control work. I installed 10-minute bubbles on the two poles I use regularly, and find that they're as good as a tribrach setup in practical use.

It's not just the bubble, though, Jim. You can have a 10 minute bullseye bubble, but if the bubble is out of adjustment, the 10 minute feature isn't worth much. I'm preaching to the choir here, but what I like about the rotating tribrach adapters like I pictured is that you can spin the top 180 and check the plate bubble in the opposite position, and check the displacement of the cross hairs in the optical plummet, and following those checks, have confidence that your setup is good. Mounted on a stable tripod, I think you can expect good results. Doesn't do away with the need for "checking the backsight" periodically throughout the day, but I think lessens the number of problems one might be inviting.

The light weight of a bipod is attractive, especially for robotic work, and I understand the desire to use it. I have one myself, and use it frequently, and do get good results, but as the need for precision and/or the liability for mistakes increases, I'd lean away from the bipod, and toward the tripod setup.

> It's not just the bubble, though, Jim. You can have a 10 minute bullseye bubble, but if the bubble is out of adjustment, the 10 minute feature isn't worth much.

True, you have to check your pole bubbles periodically, though that's easily done. Not quite as easy as rotating the tribrach adapter, but still pretty easy; you've got the gun set up anyway, might as well take a look at the pole with it.

Note that the SECO 2-meter tripods have a rotatable center pole, so they're as easy to check as rotatable tribrach adapter. I mostly use them for GPS work, but sometimes I'll use one for a backsight prism when I want the extra height.

I don't use a bipod. I own one, but I didn't care for the finickiness of getting the pole plumbed up with it. For most work I use a single bracing stick. Unless there's a lot of wind it's easy to get the pole plumb and hold it plumb very quickly. In windy conditions I'll add a second stick (a 4-foot lath works well).

For years I used a lath, and often found myself marking it off in feet and tenths for topo work. They had a limited lifespan, though; whacking through weeds and brush would eventually do them in. Next I upgraded to a length of an old Philly rod to which I added a pole point, but it was too thick to fit between the bars of most drain inlets (for getting inverts), so it was a bit limited. Then in 2009-10, when work slowed down markedly for me, I made one out of 1-1/2"x1/4" aluminum bar. I added a plumb bob point to one end and a vinyl handle to the other, and graduated it in feet, tenths and hundredths. I even engraved my company name on the blank side. (I had a lot of time on my hands for awhile there!) I like it a lot, and seldom have to pull out a tape when doing topo. Now if I can just keep from losing it...

Here are a few snaps of the stick:

I've seen those SECO 2 meter tripods, and must admit I like them. I do not own one.

Interesting tool, Jim. Nicely made. How do you use it? Not with a total station, right? With an auto level?

> Interesting tool, Jim. Nicely made. How do you use it? Not with a total station, right?

I use it to brace the prism pole. Walk up to the point, place the point of the prism pole on the desired measurement location (e.g., a monument, control point or topo shot), place your feet shoulder-width or so apart, jab the pointy end of the stick into the ground (or just set firmly if on pavement) a couple of feet in front of the pole and on line with the gun, wrap one hand around both pole and stick handle, move hand/stick up/down/in/out until the pole is plumb, grip firmly, take shot. You're basically turning yourself, the pole and the stick into a rigid tripod by maintaining a firm connection between the stick and the pole, which prevents fore/aft movement. (Firmly-planted feet control side-to-side stability.) (It's much easier -- and faster! -- to do than to explain.)

The graduations on the stick are simply a convenient means of measuring offsets, inverts, pipe sizes, tree diameters, etc. so you don't have to pull out a tape.

Nice workmanship. How did you mark the scale lines so nicely - special fixturing or just a steady hand with a chisel or scribe?

> Nice workmanship. How did you mark the scale lines so nicely - special fixturing or just a steady hand with a chisel or scribe?

Special fixturing. I set up a 1-ton arbor press with a very kludgy clamp arrangement that held a 3/8" lathe bit sharpened into a chisel shape. Then I just marked out the locations on the bar with a tape and hand-positioned the bar against a (similarly kludgy) fence for each cut. I made a second pass with a repositioned fence to mark the even tenths. (As can be seen at the 3.6-foot mark in the handle photo, I also goofed once or twice.) Numbers were simply hand stamped (1/8" dies for the tenths, 1/4" for the feet.) It was very tedious!

Nice work. Now I understand how you use this tool - thanks for the explanation. I've used a ski pole in a similar fashion, although without the graduations, which I agree is a nice idea to keep from having to pull the tape in and out of the holster.