The spread sheet, attached, data were updated using the values from the RW5 file in post 75. The zenith angle splits for observations 100-700 and 700-100 are 00å¡00'08" and 00å¡00'14" - but - the difference of elevation differences is 0.211. The latter indicates a measurement or recording error was made in either or both the Instrument Height or the Target Height.
One item that has not been addressed so far is that of obstructions near the line of sight. Preferably, to minimize inaccuracy, the line of sight should be about one meter or more above, or from, any obstruction. Observing targets where the line of sight is above a water body also introduces inaccuracies.
The Insturment and Target Heights should be measured from the station mark or monument, not the dirt around them. Normally, only when performing measurement for topo maps or photogrammetric control points, is the dirt surface measured. Other than that or some other special circumstance, Insturment and Target Heights should be measured from the station mark or monument. With Instrument an Target Heights around or more than five feet, normally, but not exclusively, the slant height provides sufficient precision for measurements.
A Lufkin measuring tape I use is pictured. Using it has saved me from carrying mistakes from the field to the office. A similar measuring tape or folding rule might do the same for others.
If you practice doing level loops, be aware that somewhere around the distance of 125 meters (400 feet) or more, that the effects of curvature and refraction start to affect elevation results.
I continue to be blessed and amazed at the wealth of knowledge here, and the willingness of those that help
Some of us have been surveying since the Great Flood. Depends on how far back you want to go.
We've grown up through these issues and worked from a grounding in the basics which helped us in the next phase as we kept up with technology.
You mentioned earlier doing your 'crash' course and obviously had much to take on board.
Any surveyor that's been around a day or two have had their share of oddities, unexplained or rational.
I'd suggest accept a routine that is ordered and proven, has built in checks and stick to it. Don't compromise your results by assumptions and self confidence.
Target heights are (as you've discovered) , critical in any survey involving height..
My routine predates TS and involved levelling by dumpy level but also T1A/ T2 and I grew up writing all heights down. I've maintained that (recording on paper) and it's dug me out of a hole more than once.
I also record leg height (station to top of legs), and full heights to targets or instrument.
I know my target and TS axis height above bottom of tribrach so can do quick checks if needed.
I don't ever want to return just to track down a simple reading error.
Typical height errors are 1.56 to 1.65 for example.
Easy to make, especially when setup in difficult, sloping topography, on on the footpath with eager onlookers asking about the job or telling you grand stories..., distractions that come with the job.
As MLS mentions beware of longer lines, water bodies, bitumen and concrete surfaces, time of day (hot sun) other atmospherics.
Take note of your data recorder when you backsight. An error is best looked into then, not later.
TS levelling can be extremely accurate when done properly.
MLSchumann, post: 334273, member: 471 wrote: The spread sheet, attached, data were updated using the values from the RW5 file in post 75. The zenith angle splits for observations 100-700 and 700-100 are 00å¡00'08" and 00å¡00'14" - but - the difference of elevation differences is 0.211. The latter indicates a measurement or recording error was made in either or both the Instrument Height or the Target Height.
MLS:
Well, you get the bonus prize again. I independently filled in the spreadsheet, using my field notes, and wouldn't you know, I entered the H.R. to 700 from 100 erroneously, into the DC as 5.23. My notes show it was 5.01!! It jives with the Instrument heights on 700 (4.99). I've attached the spread sheet which apparently brings that delta down to .009. Here's the error summary:
Thank you again.
Long live Field Books.:-)
rfc, post: 333302, member: 8882 wrote: I would think that someone running Carlson could take a Carlson SurvCE .rw5 without problems that the software might be doing something it shouldn't be, or at least warning you that the DC did something first before the desktop software gets it.
Software is probably working as designed, even though you are using an old version. From your example, it appears the end users input that created the blunder(s). You are entering two control points for horizontal and vertical control. One of these elevations does not agree with your field measurement. How do you know the elevations of these two points before you have measured them? You should hold just the starting control point for horizontal and vertical coordinates, and enter only the azimuth to the next point. If you are uncertain of the bearing and distance, then don't use it for control. Use assumed datums for your traverse. Then perform a sun shot, and bench run to get your datums established. Now transform, and rotate the reduced coordinate from your traverse to your corrected datums. This is how most did it before GNSS. Now with network GNSS we can get there quicker, but the steps are the same.
As you have noticed most errors in traversing are caused by blunders. Reading measurements, hand writing AND translations, such as your HI's and HT's. The data collector has eliminated most of the blunders:
- read data from the instrument
- write data down in a field book
- read data from field notes
- type data into a calculator or PC
- perform the computation from polar to cartesian coordinates
5 times less likely to screw up the data. Looks like you had two blunders in your data with just thre turns. Can you image a traverse of several miles, and 40+ turns.
I think keeping notes, reducing notes, checking notes, entering data, checking entered data, ect. ect. (working with the data) all build skills that are necessary for surveying. You learn to develop work flows and systems to catch blunders.
I'm not saying that modern techniques don't improve the quality of the work and save time, but I would not have wanted to skip the lessons I learned by making mistakes.
imaudigger, post: 334350, member: 7286 wrote: I think keeping notes, reducing notes, checking notes, entering data, checking entered data, ect. ect. (working with the data) all build skills that are necessary for surveying. You learn to develop work flows and systems to catch blunders.
I'm not saying that modern techniques don't improve the quality of the work and save time, but I would not have wanted to skip the lessons I learned by making mistakes.
Each and every piece of equipment and software gets tested in house.
Are the prism constants correct, does the gun and software reduce the slope to horizontal correctly, is curve and refraction applied and is it being done right, are distances reduced to state plane like they should be, is the dc calculating everything the way it should, on and on.
Everything is tested in-house, GPS, ROBOT, LEVEL, SOFTWARE,,,,,,,,,,,,,,,,,
I think all surveyors do it before going to the field. I know I do, and others do also, you need to feel comfortable. And still some silly setting can bite you, but at least you have familiarity with the equipment, never assume anything.
My robot has two measure points, you need to be sure you measure to the one that's set in the dc, just one little thing that can throw it all off.
It is the details, man... the details. I for one have many times missed those critical details. Now days it is even easier to assume and move along to come back and be bitten in the butt. The DC is only another tool and we have to pay special attention to the details. Since we are not writing down the information but storing it on the DC, we can lazy pretty fast. I don't know how many times I've changed one of the parameters while shooting, i.e. only shooting angles instead of angles and distance in Trimble Access. Another is the correct heights of equipment. Missing those change in rod heights either going up or down. Details.....
