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2.8 Set of observations

The pair tag `<obs>` groups together a set of observations which are somehow related. A typical example is a set of directions and distances observed from one stand-point. An observation section contains a set of

• horizontal directions `<direction … />`
• horizontal distances `<distance … />`
• horizontal angles `<angle … />`
• slope distances `<s-distance … />`
• zenith angles `<z-angle … />`
• azimuths `<azimuth … />`
• height differences `<dh />`

The band variance-covariance matrix of directions, distances, angles or other observations listed in one `<obs>` section may be supplied using a `<cov-mat>` pair tag with attributes `dim` (dimension) and `band` (bandwidth). The band-width of the diagonal matrix is equal to 0 and a fully-populated variance-covariance matrix has a bandwidth of `dim-1`.

Observation variances and covariances (i.e. an upper-symmetric part of the band-matrix) are written row by row between `<cov-mat>` and `</cov-mat>` tags. If present, the dimension of the variance-covariance matrix must agree with the number of observations.

The following example of variance-covariance matrix with dimension 6 and bandwidth 2 (two nonzero codiagonals and three zero codiagonals)

 ```[ 1.1 0.1 0.2 0 0 0 0.1 1.2 0.3 0.4 0 0 0.2 0.3 1.3 0.5 0.6 0 0 0.4 0.5 1.4 0.7 0.8 0 0 0.6 0.7 1.5 0.9 0 0 0 0.8 0.9 1.6 ] ```

is coded in XML as

 ``` 1.1 0.1 0.2 1.2 0.3 0.4 1.3 0.5 0.6 1.4 0.7 0.8 1.5 0.9 1.6 ```

If two or more sets of directions with different orientations are observed from a stand-point, they must be placed in different `<obs>` sections. The value of an orientation angle can be explicitly stated with an attribute `orientation="…"`. Normally, it is more convenient to let the program calculate approximate values of orientations needed for the adjustment. If directions are present, then the attribute `station` must be defined.

Optional attribute `from_dh="…"` enables to enter implicit height of instrument for all observations within the `<obs>` pair tag.

Observed distances are expressed in meters, their standard deviations in millimeters. Observed directions and angles are expressed in centigrades (400) and their standard deviations in centigrade seconds.

Height differences can be entered in the `<obs>` or `<height-differences>` section. If entered in the `<obs>` section, the `dist="..."` parameter is ignored (Height differences).

Example

 ``` 100.00 100.00 100.00 25.00 ```

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This document was generated by Ales Cepek on March 25, 2014 using texi2html 1.82.