### which method advisable and accurate to use in building gridline

Sir,i have some issues to ask about getting started for building layout such foundation and gridline offset,which method advisable and accurate to use in 300m x 108m building by coordinates method or angle/chaining method.thank you sir i realy need ur advise.thank u

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#### Replies

• First what is a coordinate method and a angle/ chaining method. This is a very large building envelope.Coordinates can be used no matter how you laid the building out.Either radially or right angle.The challenge comes on how you will measure your distances.You say chain, are you talking of a steel tape.This was done at one time  before EDM's or Total Station. But temperature  correction played a big part in this method.Also how good one was at chaining, I would ask anyone on their skill at this.

Or you could use a invar nickel tape with about one-thirtieth correction of a ordinary steel tape. This is not a easy task on a building this large. Even today temperature will play in to how you do this, Angles and distance with a Total Station as Ted has also indicated . Heat waves play a part on how good your angles are. A umbrella over the gun midday helps. But turn your angles early before the heat waves start as already been said.

Daniel made some good points and A Murali babu did also. No matter how you do it Radially or Right angles,I would check my corners for 90 degrees and the diagonal distances. All instruments contain a small error so always on something like this double center the gun on your 90 degree angles and your equipment being correct, instrument and rods are most important. Builders work off of 90 degrees and diagonals.

Most do not understand coordinates, that is your job. So i am still lost at your question on coordinates because you can use coordinates no matter how you do it but a EDM is always better for you to measure with.

• Correct.. i agrre with Billy Brooks, and ill say it again EDM is the better  to make a measurement this days..

• I have the same question as Billy. Any position, regardless of how it is established can be expressed in coordinates. It is said that GPS is the most precise method of measuring distance but there is a difference between distance measurement & positional tolerance. Do the plans & specifications specify a required minimum positional tolerance? The continuing education courses I have taken on construction surveying over the years all recommend setting lots of reference points & always check & recheck your work. Some checks offer a stronger solution than others but if you keep your instruments in good calibration, do good careful work & don't skimp on checks, you are not likely to have any problems. The biggest source of errors by far that I have witnessed in construction have been caused by errors in the plans or misinterpretation of the plans. Most surveyors can do better than a centimeter or two in 300 meters but spread out over a 300 meter distance, it is doubtful it will ever be noticed.

• Dear friend,

Co-ordinate method is the best suited for this kind of jobs. Steps.

1. Run a traverse around the site and do the correction based on bowditch rule.

2. plot the points and superimpose the proposed building and extract the co-ordinated of the required corners, center of columns etc.

3. stake these points at site.

That's it

Regards

A Murali babu

Regards

A Murali babu

• Good day  My Dear Colleague Surveyor and  My Dear Murali Babu,

Just an opinion

From my knowledge " BOWDITCH " method is not suitable with building and grid line.

It is because of this method is adjusting both of the angle and the Distance, which means GRID LINE is a fix distance where we cannot adjust distance in the traverse STN to STN .

Distance is fix, what we ( shoot ) got is what we get, No adjustment in that, but angle adjustment is a YES.. Do the True Bearing Adjustment,  Normal steps M+/- Correction and C+/- Correction as per Traversing result should close to 1:80000 or more. But still we get a little bit of an error here and there when we apply the Working Coordinates, where our coordinates runs around 3 mm to 7 mm, X or Y, even more depends on closing, But that not means we have to use Bowditch Method, there is other way to adjust those error...

For Me Bowditch rule only can be use in Road or Rail works, which had the alignment,

It is because the Traverse that been made is an open travers From 1 known STN to another Known that already been set up using GPS,

Just an Opinion from my knowledge, please do to Correct me if  i am wrong

But for the one who had problem with what i am saying about the "A little  Here and There Error" after traverse adjustment been made, still this  +/- 3 to 15 mm or more in X or Y,

can e-mail to me alisurvey75@yahoo.com their Traverse Booking/sheets, Close or an open one, and ill adjust it for you and send it back for your checking again, if agree with the result and wanted to learn ill be happy to teach the lesson

Just an opinion...

Alisurvey

• Dear Alisurvey,

I agree with you partially. The only way to correct open traverse or closed traverse is to give the correction for both angle and distance. If not done the errors creep into, due to several reasons like, local attraction, errors in the instrument, prism constants etc.. so it is better we close the mis-closure before doing any survey. regarding to road and rail surveys, it is mostly open traverse, maybe with known co-ordinates fixed by GPS or any other method. We do the open traverse and then close them with bowditch rule. In a closed traverse as we are discussing for the grid line, I have done several projects in the same lines as explained by me and have achieved accepatable results.In most of the cased i have achieved accuracy of more than 10000. In case you need the calculations and correction excel templates please visit our website www.esurveying.net. here you can download free templates for both open and closed traverse.

Regards

A Murali babu

• Thank you A Murali babu..

• Rey, your question has a few key phrases:

-angle/chaining method

Your equipment is a theodolite and chain.

-coordinates method

Create coordinates for any method you choose.

-300m x 108m building

This is a large footprint.

-foundation and gridline offset

This is a good approach when using a theodolite and chain.

I would create a baseline, 10 or 20 meters away from the building (or wherever practical), parallel with the longest building dimension, and chain in the points for grid-line.

I would then create baselines for the other three sides, turning only 90 degree angles (and sets of direct/reverse observations, of course), and make sure you tie-in/adjust to your original baseline before marking your grid-line points for these additional baselines.

Depending on MANY factors about the job I do not know, you are now prepared to layout foundations.

Grid-line works well for foundations because there is little or no vertical work obstructing your line of sight.

The great thing about this type of control is you can backsight the grid on the other side of the building to furnish the workers reference lines without turning any angles, or chaining, as you can set up on the perpendicular baseline and perform the same action.

And, with baselines, offsets are very easy to install. Just use a ruler.

Need a quick 1 meter offset?

Measure and mark it on your occupy baseline, and on the backsight baseline on the other side of the building, set up and go. This measure and mark routine does not require great angular precision. If you have to turn a 90, buck in on your baseline.

You get fast at this.

Also, when line of sight permits, "bucking in" can be done almost anywhere on site if you have boxed in the building with baselines properly. Better than two-point resection in many cases.

When vertical or elevated work will obstruct your line of sight across the building, establish practical offsets, such as one meter.

A theodolite and chain makes baseline/control work difficult by comparison to a total station, but once you complete your baselines, it is not so bad.

But if any of you try to lay a hand on my robot....grrrrrr!!!

• Maybe I am unclear of how the grid is being calculated? if it is not in CAD then is it being done from plans and only in the data collector or what? Please give more information thank you

Not a Surveyor

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