ties as uncorrelated, sometimes all with the same preci-
sion or as absolutely precise and constant, leads to a
diagonal structure of the corresponding weight matrix.
This simplification may be made for different reasons.
Often no correlations between the coordinates are known,
which is normally the case when they are taken from a
given network. Also computational aspects are sometimes
the reason, because this diagonal structure is easy to
handle. And often the precision of the control points
compared to the photogrammetric measurements is regarded
as being much better; that is at least in close range
photogrammetry and also in some aerial applications, de-
pending on scale, not true.
The theoretically rigorous case, that the full covariance
matrix is available, is seldom given, possibly for net-
works which are especially established for that purpose.
A practicable compromise would in many cases be the use of
substitute matrices, which should represent the stochastic
properties including correlations quite realistically
(Molenaar /10/).
2.3 Improvements of the mathematical model
The functional models, especially the introduction of
additional parameters for supposed systematic errors,
shoud be verified by significance tests to avoid weakening
the whole system.
Concerning the stochastic model for the adjustment of
heterogenous data the possibility of estimating variance
components should be taken into account. This topic will
not be treated here and also the following considerations
concerning computational aspects do not include possible
consequences of a variance component estimation.
3. SOME REMARKS ON COMPUTATIONAL ASPECTS
In classsical bundle block adjustment for aerotriangula-
tion the concept of partly reduced normal equations from
which the point unknowns were eliminated, has proved to be
very effective.
By extending the method to include a variety of non-
photogrammetric data, the resulting structures can be much
more general.
A concept for the efficient treatment of such combined
systems will be given in the following. For the most part
it has been realized in a program package (Müller, Stepha-
ni /11/), which is used for many practical projects.
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