2.9 Directions

Directions are expressed with the following attributes in an empty-element tag <direction />

• to = "…" target point identification
• val = "…" observed direction; see section Angular units
• stdev = "…" standard deviation (optional)
• from_dh = "…" instrument height (optional)
• to_dh = "…" reflector/target height (optional)

The standard deviation is an optional attribute. However since all observations in the adjustment must have their weights defined, the standard deviation must be given either explicitly with the attribute stdev="…" or implicitly with <points-observation direction-stdev="…" > or with a variance-covariance matrix for the given observation set. A similar approach applies to all the observations (distances, angles, etc.)

All directions in the given <obs> tag (see section Set of observations) share a common orientation shift, which is an implicit adjustment unknown parameter defining relation between the stand point directions and bearings

direction_AB + orientation shift_A = bearing_AB.

Because one <obs> tag defines one orientation shift for all its directions, stand point id must be given in the <obs from="id"> tag, using attribute from, which in turn must not be used in <direction /> tags, to avoid unintentional discrepancies.

Example

<direction  to=  "2" val="0.0000"  stdev="10.0" />
<direction  to="416" val="63.9347" />

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