he union Figure 2: Parameterization of the building primitive with
gable roof
8
BO
IUE
2. Projection of the wire frame model of the primitive
however into the image section after hidden line removal. This
0 tasks: projection is based on approximate values for the
ig Image height and default values for the parameters of the
t of the primitive. If it is not the first primitive the height of
nproving the base level of the previous primitive is used. If the
primitive has already been selected, the old parame-
chtation ters are used as default.
with the 3. Interactive adaptation of the form of the wire frame
ie image model to the image content (cf. below). During this
in order action the pose and form parameters are determined
and the primitive is visualized in real time using an ap-
; proximate height of the primitive. The operator may
el-image : : T
: choose that resolution of the image which is suited
E best for this interaction.
: internal During this process a snap-function can be activated.
? coordi- Based on some user specified snap-radius relations to
> system already extracted primitives are automatically estab-
width b lished and in case they are found shown to the oper-
ordinates ator and visualized at the screen. This enables gluing
ordinate of points, edges and especially faces of neighboring
primitives.
The accuracy of this adaptation can be reduced if a
subsequent fine tuning takes place.
4. Height determination using either an automatic tool
(cf. below) or interactively a second image if it is the
first primitive within the CSG-model of the building.
Optional, the parameters can be fine tuned using a
least squares adjustment (cf. below) after matching
the az- the wire frame model to the edges extracted in all
building available images.
m. 5. (optional) Visualization of the parts extracted so far
s implic- for checking the result.
ecify the
Only the automatic fine tunig in step 4 requires digital im-
ages. If a sufficiently accurate adaptation of the model to
the images is available the procedure can also be realized in
win intel an Analytical Plotter with Stereosuperimposition.
providing Extracting Prisms. The extraction of prisms relies on auto-
matically extracted image edges. They have to be provided by
action. Gi some edge extraction procedure. The operator interactively
n several selects a sequence of image edges representing the ground
plan at eave level, thus assuming all the selected image edges
to lie in a horizontal plane. Neighboring image edges are
reviously linked by intersection. In case of strong shadows where no
:e of type image edges are available, the operator also can define break
Points of the polygonal ground plan. The geometry also may
263
select operation and model je model data base |
À Ÿ
| | project |
Y
| adapt pose and form |
A Y
determ. height and tune fine |
Y
| operator interaction | | visualize |
Table 1: Steps of semiautomatic building extraction
Figure 3: Extracted building block consisting of two saddle
roof primitives, a box and a pyramid
be changed interactively if necessary. Using an automatic tool
or by interaction the height of the eave level is determined.
Using the same procedure as for interactively adapting the
parameters of CSG-primitives the height of the prism, i. e.
the ground level is found.
2.3 Parameter Adaptation
The interactive adaptation of the form and pose parameters
is performed in monocular mode. Stereo display is not nec-
essary. An extension of the interactive steps for the case of a
stereo display is simple.
The adaptation of the parameters is done in a sequence of
steps, each specifying one or two parameters of the model.
The parameters are changed in dependence of the sequence of
two points specified by mouse clicks and in dependence of the
type of primitive. Therefore the number of interaction steps
is between 50 % and 100 % of the number of parameters.
Which parameter actually is to be adapted is stored in a so
called association table setup to support intuitive interaction.
The association table is build up according to the following
rules:
The first of the two points chosen is the reference
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
