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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
<direction … />
<distance … />
<angle … />
<s-distance … />
<z-angle … />
<azimuth … />
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
<cov-mat dim="6" band="2"> 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 </cov-mat> |
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.
<obs from="418"> <direction to= "2" val="0.0000" stdev="10.0" /> <direction to="416" val="63.9347" stdev="10.0" /> <direction to="420" val="336.3190" stdev="10.0" /> <distance to="420" val="246.594" stdev="5.0" /> </obs> <obs from="418"> <direction to= "2" val="0.0000" /> <direction to="416" val="63.9347" /> <direction to="420" val="336.3190" /> <distance to="420" val="246.594" /> <cov-mat dim="4" band="0"> 100.00 100.00 100.00 25.00 </cov-mat> </obs> |
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