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Message:

> Hello aleksandar95,
> 
> > I would like to send you the project I have already done, where I have input the values for sigma a, sigma b, and sigma c based on my experience and the explanations from the website. I would appreciate it if you could review it and tell me whether these values are suitable for this type of project.
> 
> A common approach to evaluate the a-priori stochastic model (i.e. σa, σb, and σc) is the [link=https://software.applied-geodesy.org/wiki/least-squares-adjustment/variance-component-estimation]variance-component estimation[/link]. The following image shows an example of the estimation results.
> 
> [img]https://software.applied-geodesy.org/wiki/_media/user-interface/jag3d_ui_variance_component_estimation.png[/img]
> 
> 
> 
> The most popular variance-component is the estimated a-posteriori variance of the unit weight. This variance is evaluated within the global test. However, the residuals and redundancies of the network can be grouped in order to derive sub-components. In JAG3D, the components refer to the observation type. Since the stochastic model for each terrestrial observation type consists of up to three components (i.e. σa, σb and σc), JAG3D derives sub-components of these variances. Each specific variance-component can be analysed in the same way as the global variance-component. The expectation value for each variance-component is [tex]E\{\hat{\sigma}^2\} = \sigma^2[/tex] (by convention, [tex]\sigma^2 = 1[/tex] in JAG3D). 
> 
> 
> > What I am most interested in is what sigma a represents.
> 
> I have [link=https://software.applied-geodesy.org/forum/?id=14823]already[/link] [link=https://software.applied-geodesy.org/forum/?id=14825]answered[/link] this question and I am not sure how this question can be answered if you make your project available. 
> 
> > Is it the a priori standard deviation or not? 
> 
> [link=https://software.applied-geodesy.org/forum/?id=14825]Have you read my answer to the same question?[/link] The answer is still yes. 
> 
> > Since we have concluded that sigma b is the instrument's accuracy. 
> 
> The σb is an a-priori standard deviation which depends on the length d.
> 
> 
> > What interests me the most is what sigma a represents
> 
> It is not helpful if you ask me the same question over and over again without responding to my answer. In summery, σa is an a-priori standard deviation. It is independent of the length and is a random error of each single observation. This value is derived from empirical values for the instrument and the measurement process. 
> 
> Kind regards
> Micha

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