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ceed. 2.4.3
Correlation in the subpixel range: The basic information
about this theme is presented by means of four text lines and
two figures (see fig. 3). The sequence of the text lines can be
repeated or stopped. Additional information such as formulas
and explanation of the parameters is displayed when clicking
on the field "INFORMATION". The exercise is started by
pointing to "TASK". The contents of the theme covers the
correlation within a profile, which means the target matrix is
shifted in one direction only. This topic is easier to understand
than correlation in two dimensions. It serves here as an
introduction, but has in itself practical application for height
determinations.
THEME 2: CORRELATION IN THE SUBPIXEL RANGE RP
b * gl
a
“>
X - THE TARGET AREA HAS TO BE SHIFTED A SMALL AMOUNT
[ FROM AN APPROXIMATE POSITION
&
Target area - THE TARGET AREA HAS TO CHANGE IN DENSITY AS WELL
92 - THE SOLUTION IS FOUND BY A LEAST - SQUARE ADJUSTMENT
- THE OBSERVATION EQUATION CAN BE FORMULATED AS:
v2gi(g*a*b*gi(e) *c- ga(s)
Information
Search area
INFORMATION
Fig. 3. Theme 'Correlation in the subpixel range' from the CAL
program "LDIP". At this moment of the sequence all text lines
are displayed as well as the additional information (in smaller
print). The sequence of the text lines can be restarted by
activating the field 'REPEAT'.
2.4.4 Correlation in the subpixel range - task 2.1: This
exercise requires to find the coefficients of the observation
equations which have to be read from the attached figure and
set into the matrix and the vector areas. Thereafter the
calculation of the normal equations is started and can be
watched. The precise position of the target area and its
accuracy have to be calculated by the student again. He or
she uses the integrated pocket calculator for this purpose
(see fig. 4). The results have to be entered into the keyboard
and they will be displayed at the premarked result windows.
All input values are analysed and commented by the program.
THEME 2: CORRELATION IN THE SUBPIXEL RANGE RP
COMPLETE OBSERVATION AND COMPUTE UNKNOWNS!
TASK 2.1: Observations: v = A * x - 1 e
=
Fill in A-matrix and 1-vector
$11.92 0.00 1.00 1.00 1.00
i319 BÍ m.
10 040 9. !
= |0.00 9.00 1.00 8.00
t Ll EE cj gm
7 (_n Colculator — ) 000 100 1.00 1.00
5 t ladjustment: viv = Minimum
| LL 29% 90. [f] - [4
LJ j 4 -
2 rit x: 0.920 0.00 3100 700 e 27.00
1 H
pram [Solution of normal equations :
EE EE
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081 ;
m ENTER OFF §| «
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rod i
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m
KNOWLEDGE RETURN TO MAIN MENU
CALCULATOR EXE ER ER |
Fig. 4. Exercise to the theme 'Correlation in the subpixel range
- one dimension'. The unknowns of the correlation are
determined by an integrated calculator.
63
2.4.5 Automatic measurement of real réseau images: The
theoretical treatment is now supplemented with practical
réseau images. The presented knowledge contains again a
sequence of lines of text, dynamic figures, formulas and
recommendation of literature to read (compare fig. 5). They
are presented in various levels.
THEME 4:
AUTOMATIC MEASUREMENT RP"
of Real Réseau Images
x :;^$ has fine crosses in the image
plane, which are exposed onto the film
£$ show the crosses
2* can be carried out
and more accurate
- The trensformation of the measured crosses to the
coordinate values of the :z XH
reveals the film deformatio
anner deficencies
à zoom factor: [+] - Imaged object points can be corrected by means of an
affi i: where the sorrounding
ntrol points E
Select réseau image
INFORMATION TASK REPEAT RETURN TO MAIN MENU STOP
Fig. 5. Screen image for the theme 'Automatic Measurement
of Real Réseau Images’. All the text lines are displayed by
now; additional information will be shown when ‘clicking’ on
the underlined key-words. A hypertext window will then
display more text, formulas, figures or recommended litera-
ture. The image at the left side of the screen can be inter-
changed and zoomed. The selectable images are taken from
project work.
Additional information is received by activating either the
keywords in the text or an icon. A hypertext window appears
which can be shifted to another place, if it hides information.
The exercise with real réseau images starts with adjusting the
template in size, rotation and geometric resolution (pixel size)
to the crosses of the réseau image. The first two crosses are
measured by pointing at the approximate location. By means
of the derived transformation parameters the measuring can
now occur automatically. The speed of measurement and the
setting accuracy is displayed. Various sets of transformation
(affine or projective, with all crosses or with four surrounding
crosses) are carried out, and the residuals at the crosses are
displayed. The results demonstrate the advantages of the
réseau camera.
2.5 Some experiences from the development
The development of "LDIP" occurred in the usual steps
design, programming, testing, and documentation.
The design of the program comprises the screen images for
'Knowledge' and 'Task, the user interface and the program
structure. The screen images are designed according to the
technical contents, here "Automatic measurement ". The
practical exercises also determine the amount of information
which has to be presented in 'knowledge', for example the
formulas, the figures, their expressions, etc. Computational
tasks should not be too lengthy. Parts of the computations will
run automatically and intermediate results are displayed. The
user interface was designed according to standards estab-
lished in previous CAL programs by the author. For example,
the operation has to be as simple as possible. The sequence
at the normal use of the program as well as all possible
manipulations had to be specified for the programmers.
Programming of the "LDIP" software was split into 'user
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B6. Vienna 1996
