International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B3. Istanbul 2004
4.3.3 Computing of parameters : Now four known points
are available. The aim is to find out a way to digitize their
image-coordinates and then it is possible to compute the eight
parameters.
given in (2) :
c
The to (1) corresponding linear equations are
bl.x + b2.y + b3 — X.(b7.x + b8.y + 1)=0
bl.x + b2.y + b3 — X.(b7.x + b8.y) = X
b4.x + b5.y + b6 — Y.(b7.x + b8.y + 1)=0
b4.x + b5.y + b6 — Y.(b7.x + b8.y) = Y
4.4 Measurement tools
4.4.1 | Image-coordinates measurement : The first element
that could be exploited is the possibility to measure now image-
coordinates directly in the photography.
Figure 6. Photography of a frontage
The management of the display size of the image and the metric
units is one of the encountered problems. There is given a scale
ratio from 4/3 to obtain the real pixel-coordinates. Whatever we
use as unit or scale ratio, the homogeneity of the system
provides correct results, but we choose to apply this scale ratio
of 4/3 to obtain real pixel-coordinates in order to compute the
parameters bl to b8 which can be used in the futur with the
same image and eventually other applications.
4.5 Information extraction
4.5.1 Horizontal division : The first information we want to
extract from the photography of a frontage is simply the number
of stories of the building. This operation is generally easy to
realize. But in the same time, we can determine the size of each
story and in this way find out not only a thematic but also a
geometric information.
The implemented tool performs to associate a measured height
to each story.
A semi-automatic process consist in a first time to measure the
height of the first floor often different than the height of the
other floors, then to measure the cumulative height of the
supplementary upper floors.
550
Etape 1 | Etape2 Etape3 | tace 3 eee Jr]
Divisions Horizontales
Xv 35,397 Yi. 21,79
Ptt:| 9,10 ET T
Beli [Br Distance :| 15,82 |
“Rez de Chaussée —-———-——
hauteur : 2,88
pn Etage(s) TEE irit
nombre d'étaga(s) 1 6
, hauteur par étage : 2,64
Figure 7. Interface for the measurement of the stories
An easy operation gives the number of stories from the
cumulative height and the means height of the stories. This
procedure needs to define a minimal story-height and can
proving out to be insufficient in the case of a great number of
stories.
We can observe that for the measurement of the heights of the
stories we use only the Y component because the coordinate
system is oriented accordingly to the frontage (X-axe oriented
from left to right, Y-axe oriented from down to up).This allows
to measure to points (first down, second up) that are not place
onto a same strength vertical.
4.5.2 Other divisions : The aim of this fonction is to
describe other phenomenon localized directly on a precise floor.
It can be indeed of interest to point out for instance balconies,
loggias, recesses, porchs (Figure 8), etc.
In order to simplify the designation of such elements, it has
been decided to subdivide vertically the previous defined
stories.
The tool perfoms to realize this step quickly. In fact, the only
operator's manipulation is to digitize one point for each vertical
subdividing line.
Figure 8. Particular subdividing parts of frontages
The following example (Figure 9) shows how to proceed with a
recess part. In this case, the operator must digitize a point on
each side but he has to remain in the plane of the frontage. Here
we have to measure two points on the lower part of the recess
and move lightly the cursor on the same X-coordinates. In this
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