.A METHOD F'OR THREE .....DIMENSIONAL MODELS GENERA'TION' FROM DIGITA L
IIVIA:GE CORRELAT'ION
<It
lVI.Fondell:i
Facol.ta di Ingegneria, University of Florence
Via di Santa Marta, 3
50139 Firenze, Ital.Y'
Commission: no. III
\,Vorking grcrup no., 111/3
Abstract
The paper gives an o'verv:iLew of' the pro;b2ems in digital l.Jnage correlation and analyzes the results achieved till now in the
field of robotics and of analyti.cal photogrammetryr.
Criteria and fundamental concepts for a general approach to
the problem are given, as well as the analytical definition and
the practical. methoii designed.
Furthermore some simulations and some applications 01" the
suggested method in the field o'f' urban surveY" are explained with,
the results achieved.
A comparison is a1,so carried out between these techniques
and classic digital stereoplotting in order to' asses the reliabi.....
lity of the method.
INTRODUCTION
1.
The natUX"al system of stereoscopic perception gives a baSis
for rat:ilonal design of three-d:iimensional mo'dels generation' from
digital. image correlation for robo:tic purpose and to' devel.op the
automatic pho"togrammetr'ie methods.
It is notorious that in the process of natural visua~ per'ception:, either monocular or binocular, three essential. elements'
appear to' be linked together, and preeisely: the e:reba1l" the
optic nerve and the, visual centers of the' brain.. The eyeball contains the· d'ioptr-j~c apparatus fb"T t-o~ detect the o'bjective reality
and to record the relative signals. The visual imputl.ses pro'd:uced
by' the impact o:f light on the retina are transmitted after tOl the
brain',! through th'e optic nerve" where th,e sensation' of vision' comes to! consciousness ...
The retina eo'ustitutes the beginning element o·f visual per-
189
obj:ect, the image, is sharp,ly' on
yell.ow spot, where the pe'r .....
ed tel
and comes from a
coniugate' p~ixel.s, owners
yellow spots. The
eye are not exactly.of' virual threethe poss
per ....
the same task by means
electronic correlation techni ....
ques or <eoherent· op,tical proceo.,;;;.,.a...l.lJ",Fc.. ... Investigatio1:'l's have carried
carrelat
photogrammetr'ic instruments
resolve
the smalsupporting a specified accuracY'
method are presented
the
from digital s t e;r e 0 ....
n"'t:/";."a"""!:l'm,m,o~·Y"'!rr are
toward automated
ess
AN
TO
.l..J.U,I..I.l.l,;,-_
IlVIENSI Or.~A L MODE LS GENERA TION
2.
similarlLty between the direct binocular visielJm and the
indirect: s'tere,osc
generat~ion
space models is notable in
many resp
, both image
in, this different
differences between the c01illitIga ite
are,
stereo:scop'ic
Actual pro;cedure in stereop-lott,ing, work our.t coordinates
point DY' pO'int·,;- after abso'l.ute orientaticn'1; of stereo'grams. AIl
sUrch: fn-tersectioD
tGgether' form a three-dimensional.
model, geometrically:
the photographed objiect.
digital image
a view to' simplifY',
I)lerC'eptio'n.
c
S0011
as
1
After' conversion: from opirical form to d:iJ.gital f'orm
eeln:iugate images,; this ext ens iOlll) is p,clssibile if' the different
gra:y: levels are well distributed in the
er representation.
Otherwise, the pro'bClem to be solved b:y- means histogram equa1i .....
sation or' ima.ge enhancemenii, and restoration.
Numerous technd.ques fOT' computing the correlation functio'n
are' wel.:L known, and some· o,f ihem are wid e I;)'"" used
analo:g CT'
in digita~ form. Very important on' the subject are tl f'o,r istance,
the direct digital correlat
the FO'11Urier transform co·rre,la .....
1t,i~')ilm and the miscellaneous methe)ds
•
An easy' procedure for digital co.rrelation of' coniugate images may
the best; oYerlappin.€
cClm!i1Wgate raster representa ....
t,ians,grayr le:vel by graY" 1
,
to detect the
tive
ferences or' lQ.cal ho:rizontal parallaxes ..
Tlte techrl'iques f()T comparisolllJ ana: correlation 01' different
images of' the same
were
p!resent..
the 00niu:gate p;ixe1.s are p,laced along' a predetermined line the image
correla1iiorlJ becomes one-dimen-sioJTJJal /5/'.
Viery" use·itt!. in these operat,io:ns are somet:imes t-he digital
edge extraction tecMiquecs f'or to increase the contrast of' ra .....
ster data and to improve the best fitt,iImg of' coniugate p1ixels.
From the parallaxes it, is' po,ssible" fo'llowimg, to; determine
the a':iigital elevation data and to' o,'btain the three-dimensional
model.. 0\£' pho,to'graphed objiecit; through s:uitable elaborations.
In pracitice this pro'cedure invo·lves: (1) analysiS 0'1' histogams and selectio,n of' gray :Level.s; (2) best 1'itting o;! co:.....
niagate selec1tions; (3) measuring parallax; (4) storing and
smoo1l1:lting Ol! the parallax data; (5) formation of' the digital model; (6) re'p,eating steps f'ar (llther' selecti€ll1l!S un:til correlation
is complete; (7) formtdat;ien o',:r the f'inal mOide! and ourtpu-t.
The application of' 1this procedure may; be no-t to' knoW' tne
constant of stereometric camera.s .. Orientatio:n and size o'f model
are a'btained" if' necessary-" through successive iteration from
approximate displacements.
~e
analytical procedure f'O;T this generat,ion of models is
not: expensive, because raster data are conveniently wOTk on.
samp1.. ing' and quantizati.orIl selected are imp-oxtant
accuracy' o:f the determinatio:n. T'o'o coarse resolutio]J:
miss
impo:rtant deta
,too
may be take
mwen;
1 1
a new sam .....
space. Some improvement can be aschieved
pIing or different amplitude of' gra:r levels.
It is, interesting to, observe after
that each po'i~t of
three-dimensional model
spo't by, :f'our parameters: X
coordinates and gray" level.•
APPLICATIONS AND CONCLUSIONS
3..
The suggest criteria are ap;ply'ed
a te'st
mentation~ at, Un:iversity. (1"£' Florenee, witbJ kind coop
Pro.'fessor V.. Cappellmi and another researchers.
For esp1erimental tes't
selected a stereo'gram
o'f V'ernazza, taken :lTor cartograpll'ic purpose
of about 500 meters (Juxthorization no .. 58" 2-2 .....1981)
Figure 1
1
tIre site
altitUlde
I»
F'igllre
2
After a prel,iminary: stereop'lotting of' this stereogram~ 'the
coniugate images are converted in digital form and prepro'cessed.
for to remove noise and I'or equalization. FigutTe 1. sho~ws grayr
levels hd:.st ogram
righ:t phot o gram .,
The digital correlatio'n, has made on' rasterized images atdifferent gray' 1.evels and the discrepancies of' overlapping: are
computed by:'
between. the cQniu:gate selections /4/'.
gur'a 2 shows the resul,ts o,f se1ec;1'.i011] from 1.70' t'o, 255 grayve~s and Figwre 3 sh'o,ws t-he resul..t-s from 100 to: 255 gray- leve-1s
of the S'8me tested stereogram.
by'
The obtained differences, or paral1axe's, are contr'O,11ed
with: photogrammetric pro'cess bef'ore the further
of data ..
step~'
t;].01:1'
The generation of' three ....dimensional model has
raetive a_perat
Four'ier
1
byr
oe
st~ep
3
Figure
ting at"· irregularly- spaced data
/6/".
The morpho:logy of' mO'de~ is checked by comparison' wiirh'. topographic map~ Qf' Vernazza at scale 1: 500 carrie,d aut byr Regione
Ligu:ria from the same stereogram /7/
1
•
The check. has domonstrated th;e possih:ility Oi!' perfoTming'
t-hie T€liabrilityr 'Orr means this procedure whenever graY" level.s accuracyr wilJL be acceptable.
New esperiences are 1!.mder· way :f"or to' test the same pro'cedu,,-
re in;
archit'ectU!ra~
survey- and
f'OT
to iimproive the method.
Acknowledgments
The A. thanks Professor V.Cappelli:m:i, D(!)'ctors C.Conese, IJe
and L.S'UTaee f'O.T their useful cooperationr and iliscus .....
sions.,
Ippa~litQ'
194
This work is partially supported by !yiinistry o,f Pwhlic Instruction.
REFERENCES
/1/
U.V.HELAVA, Digital. Correlatio'E: in Pho'togrammetric mstru'ments. XIII Internatioinal Congress f'or Photo'grammetry. Hfelsinki" 197'6.
/2/
li.BENARD, Extraciting 3D Coordinates' of' an Oo)jiect from a Digital. Stereopair: An Automat:ed ~lretnod. ENSIPCO 1983" 12 .....16
sept:.,; Erlaugen.
M.BENARD" Aumomatic StereoplrIot',ogrammetryr: A lYIe1ihlod based:
Orll. Feature Detection amd Dynamic Pro:gTamming. Phto'grammetria.
Vol. 39, Ii. 3, sept. 1984.
/3,/
M.CLAID'S'" Digital, Terram Models 1thr'ough; Digital S'tereo Cor. . .
rela t:ion. Pho't o granllne tria , Vol. • 39, N. 4-6" nov. 1984.
/4/
V.CAPPELLINI,f M.FONDELLI, F.lV.frJINTONI" G.VANNI," Some llrigh. e£"f'iciency digital teclmiques ~f'Qr remote sensing dat'a pro:cessing'. Inrterna1iional, Archi.ves o:fr Pho,to'grarnmetry, Volume XXIII
Part: B 3. Hamburg 1980.
/5/
T.JJ. KEA'lIII>fG and P.R. WOLF', AnaljPtical Pbo:t,ogrammetry from
Digitized Image Densities. XIII TElternatio,nal Congress for
Phuto:grammetry. Ifelsiniki, 1,976.
W.R.tTAMES,:,. F'ortran' IV Pro'gram uSing Double Fourier Ser'ies
fo:1'"" Surface Fitting of' Irr'egularly Spaced Data. Co~pmer
Contribution 5. The ID'niiversity of' Kamas • Lawrence, 1966.
f71/
N.ROSSI", IJ'evoluzio:n;e concettuale della cartografia, a grandiBsima s:cala per la do:cumentazione dei cenrtri 'll!r'"bani di
interesse storicCl ar:t,ist,ico e amhiental,e e per la p'ianif'icazio:rt1,e daT paesaggio,. Documel1.t-i del. T:erritorio, N. 8" 1987.
195