is
‚on
ive
nd-
1).
DTM
be
ub—
the
23—
the
on,
ce,
wly
uch
lue
ing
ial
ion
cal
E.,
ata
tal
the
nearest DTM points can be identified and used for interpolation. The
latter can be avoided if the overlaid grid is sufficiently dense. Any
image point can then be assigned the height of the nearest DTM grid
point. The grid density can be made dependent on the radial distance
from the nadir point and the specified accuracy.
— Differential height of the object points from the DTM surface can be
acquired by parallax measurement parallel with the measurement of the
planimetric features (figure 5). The heights Zn obtained from DTM are
first corrected accordingly (dh) and are then further used for the
"image-to-model" transformation (figure 8).
X CONTROL DATA NS a“
y
\Orientat ion\correct ion\ X,
CONTROL_DATA
dh DTM
„a
|
IMAGE TO MODEL
TRANSFORMATION
|
NI
Nl
X,Y
Th no
X,Y | INTERPOLATION
— yes
MODEL TO MAP
(or ground)
TRANSFORMATION
ee == = a em = — — SE
Fig. 8: Image-to-model transformation with óh included.
Further refinement is attained by automatically assigning differential
heights to a specified series of successive object points. Hereby dif-
ferential height can be constant or variable, i.e., interpolated between
adjacent pairs of object points for which differential heights were
measured [9].
IV INFORMATION AND DATA
Among the very important issues of integrating data bases are the struc-
ture, compatibility and description of the information and data. In the
following some consideration is given to structuring because the struc-
tures tend to provide a frame of reference for compatibility and
description.
Suitable entries (or influencing factors) for structuring information and
data are:
— The overall system context (in a broad sense)
- Destinations (or role) of information and data in the system
— Process stages (or the states of input and output)
— Domains of information
— Specific context of the data base (or its use)
In the following, an outline is given of each of these main factors.
35
