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surface as the different layers of soil. This would enable a
fast continued interpolation and require a moderate data storage
capacity in the computer. The construction itself being descri-
bed in the same way would give fast and simple ways to calcula-
te cut and fill.
It is also proposed that DTMs should be provided with some "la-
bel" describing the status of the DTM. Since a terrain model is
associated with a particular project for a long time, it is
necessary to know its origin, the method of data aquisition,
point density information about quality and so on.
Markdata Consulting has recently developed a new DTM according
to these principles in cooperation with the Road Administration
and a few other consulting firms. The new DTM is basically a
string-model with possibilities to perform linear, bi-linear,
second or third degree interpolation according to topography
and application. Basic measurements with geodetic, photogrammet-
ric and cartographic methods could be merged in the DTM. Diffe-
rent layers of soils are separated and tne DTM is supplied with
an "information label".
This DTM is the first step towards a fully integrated suit of
programs for the design of interchanges. The system will be de-
veloped by Markdata Consulting in cooperation with the Road Ad-
ministration.
4.2 Combination of photogrammetric and terrestrial surveys
In the preliminary design terrestrial surveying is necessary to
establish control for the photogrammetric evaluation of aerial
photographs.
In the final design terrestrial surveying is used for many purpo-
ses. For instance in order to establish traverses for setting out
of the road centre line, to supply control points for aerial pho-
tography, for measurement. of longitudinal profiles and cross-sec-
tions etc.
A photogrammetric system for topographic data aquisition must al-
ways have a corresponding terrestrial survey system as a back up.
It should always be possible to insert terrestrial measurements
where gaps occur in the photogrammetric measurements due to vege-
tation.
Polar measurements from traverse points or other points with
known coordinates provide XYZ-coordinates for the measured points.
Depending on how the points have been selected they will complete
a photogrammetric measurement of cross-sections or a DTM.
The development of combined instrument for electro-optical distance
measurements and angle measurements (electro-optical tacheometers)
has had the effect that setting out and measurement of cross-sec-
tions is made in one operation. Setting out data can easily be cal-
culated with programmable desk or pocket calculators. At the Road
Administration the Hewlett-Packard calculators model 9820 and mo-
del 65 are used for this purpose.
