Hey guys 

I have done a survey 4 months ago, but for accuracy proposes when I repeat it again with tow kinds of prism (in total station menu was selected just mini prism).

1 Lieca round prism

2 lieca mini prism 

But the result shown me the objects relocation than preveus work, in none systematic manner, a building corner the same location the other deffren or have skew than preveus work or other building in correct location in which was read a complete building by the same prism mini or round. 

Any suggestion or ideas?

Thanks

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Yes. different prisms have different offsets,  Is normally written on the prism. Leica round is 0mm (or -30mm) to other manufacturers

Hello Mohammad,

It's wise to check the prism's you are using.

Be aware of the fact that all the Leica prism's incorporate a standard difference of -/-34,4mm, which is regarded as Leica 0 (zero) value.

So I would like to propose a small test with 3 tripods in line. 1--2--3.

Take a distance measurement from 1 to 2 plus 1 to 3.

After that that set up on 2, and measure the distance to 1 and 3.

Compare the distances. 

The first distance uses only 1x the prism constant value. When you set up from position 2 it's using 2x the prism constant value.

If possible use a seccond total station to,eleminate system failures.

hope this helps.

you can always define a new prism name + constant value in your instrument settings.

Regards, Peter

Hey there are three kinds of prism in leica TS
1 mini (17.5mm)
2 round (34 mm)
3 mini round(0)
Hellooo salem,
Acha swal kiya h aapne... bahut ae log is ka shikar hte hain pr pta na hone ki wjah se loig galat smjhne lgte hain.... ha ye sahi h ki sahi prism type na dalne bahut fark pdta h.
Jaisa prism type aap use kr rhe ho wahi prism type machine e seected b chahiye.
Or agr maloom krna ho ki actually prism constent kitna h toi uys ke .... field me total station ke aas pas prism lga kr machine se direct distance measure kre or use distance ko measuring tape se check kro... jo diffrence hoga wo prism coinstent hipiga

Hi NAYUM KHAN 

May you say in English plz

your prism constant is very valid.Normally a -30mm constant is applied for large prisms.A small prism has a different prism.

Set up test locations (possibly inside) and check everything periodically 

I agree with Grabwell Fundira above. A large prism offset is normally -30mm. It is generally to your advantage to use the same type of equipment when retracing an as built survey. MINI PRISMS ALL HAVE DIFFERENT OFFSETS THAN A LARGER PRISM. YOU MUST CHANGE THE SIZE OF THE OFFSET TO GET THE CORRECT ANSWER.

Hi Mohammad!

On the prism's mount You can read the modelname.

If You are using Leica prism, it may be:

Obviously, You must input the proper prism's constant at the beginning of the survey.

Otherwise, the distance will be affect by wrong offset.

Bye!

Carlo Alberto

The mini and the regular circle prism should have the same accuracy but the 360 degree prisms are typically 6" or 8" rated so aren't advisable for long traverses

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