# 1D parameters and datum points

Hello,

the equations defining the stochastic model are given in the Wiki. Even if the content is in German, the equations are interpretable.

Now I want to ask same questions but for 2D.
If I want to put 2 + 2ppm for distance then I need to put in distance: in oa = 2 (mm)
, oc = 2 (ppm) and ob(sqr(d))=0? is it correct?

Yes, this is correct.

What I need to put for angle(direction), if I have instrument standard of 1'' - 0.31mgon, what to put in oa = (mgon), oc = (mm) and ob(sqr(d))= (mm)?

You have to set σa = 0,3 mgon. If you don't have any further uncertainty, the σb and σc are zeros. Usually, a centring uncertainty has to taken into account. Let say, you are able to point the centre of the target with 1 mm, in this case, you can specify this further uncertainty by σc = 1 mm.

Also for example if I have 4(x, y) points can I put datum on point 1 (both X and Y) and on point 2 but to put datum only on Y? Is this possible?

Yes, but this is a academic construction not used in any practical application. The stochastic points can be diverted from its intended use to reach such a configuration. For instance, you have the points A, B, C and D and xA, yA and yB should be used for defining the datum, xB, C and D are parameters to be estimated. C and D are new points but A and B are stochastic points. Create a file like

A <yA> <xA>  0.00001  0.00001
B <yB> <xB>  0.00001  100.0

The three components that define the datum are fixed (due to the large weight) and xB is a (more or less) free parameter.

kind regards
Micha

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