The problems involved in processing remotely sensed data are defined within the contex of the total information system structure. The correlation of various data sets through georeferencing and cataloging is emphasized along with geometric rectification. The sources and types of possible geometric errors are outlined

Billingsley, F. C.

English

NASA Technical Reports Server

2.3 WORKSHOP RATIONALE 
F. C. B i l l i n g s l e y ,  JPL' 
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For t h e  f u t u r e ,  we've g o t  t o  d o r r y  about  how we can  a c t u a l l y  do d a t a  process-  
i n g  i n  a manner t h a t  produces data  which is of g r e a t e r  accuracy  by t h e  time we 
u s e  it. Very l i k e l y  we are going  t o  be d e a l i n g  wi th  a set  of s e n s o r s  which 
may n o t  be on a g iven  s p a c e c r a f t .  T h i s  s a y s  t h a t  t h e  d a t a  may or may n o t  be 
opt imized for  t h e  t y p e  of p r o c e s s i n g  which w e  a r e  going t o  apply.  This i n  
tu;n g i v e s  u s  some i m p l i c a t i o n s  on t h e  p r o c e s s i n g  needed p r i o r  t o  a n a l y s i s ,  
i c . .  geographic  r e g i s t r a t i o n  and t h e  whole q u e s t i c n  of how t o  g e t  d a t a  geo- 
c o d 4  and i n  c o n d i t i o n  t o  r e g i s t e r  one set  o f  d a t a  t o  t h e  other .  There are 
a l so  q u e s t i o n s  of  on-board process ing ,  d a t a  compression, and v a r i o u s  s p e c i a l  
p ipeAr?c  p a r a l l e l  p r o c e s s o r  e lements  which are going t o  be r e q u i r e d  t o  g e t  t h e  
d a t a  through t h e  system i n  t h e  r e a s o n a b l e  time. 
As i l l u s t r a t e d  by F i g u r e  1 ,  we're d e a l i n g  w i t h  a set  of p r o c e s s i n g  i n  one 
p i e c e  of t h i s  t o t a l  system s t a r t i n g  wi th  a s e n s o r ,  a set  t h a t  goes through a 
preprocess ing  s t e p ,  becomes a r c h i v e d ,  and i s  e x t r a c t e d  from t h e  a r c h i v e :  t h e  
d a t a  is processed and f i n a l l y  a p p l i e d  t o  uxer  models. We're t r y i n g  t o  p u t  t h e  
d a t a  i n  a c o n d i t i o n  so t h a t  when t h e  u s e r s  r e q u e s t  through t h e  s:r..tem they  can 
g e t  t h e  set  of d a t a  t h e y  want, i n  t h e  c o n d i t i o n  t h e y  r e q u i r e .  
I n  t h e  g e n e r a l  a r e a  of' p r e p r o c e s s i n g  we a r e  going t o  be d e a l i n g  w i t h  a number 
of p o t e n t i a l  t o p i c s ,  among which  i s  geometr ic  r e c t i f i c a t i o n  ( w h i c h ,  of cour se ,  
is o u r  main i n t e r e s t  here) .  The q u e s t i o n  of r a d i o m e t r i c  preprocess ing  i n  
terms of t h i s  conference  comes i n t o  p l a y  r e g a r d i n g  whether or n o t  t h e  rad io-  
metric p r o p e r t i e s  o f  t h e  d a t a  have any effect  on o u r  a b i l i t y  t o  do any o f  t h e  
geometr ic  o p e r a t i o n s  r e q u i r e d .  For i n s t a n c e  i n  t h e  e a r l i e r  Landsats ,  u n t i l  
t h e  d a t a  were p r o p e r l y  d e s t r i p e d ,  t h e  c o r r e l a t i o n s  which were done f o r  r e g i s -  
t r a t i o n  of ground control  p o i n t s  tended t o  l o c k  i n  on a s t r i p i n g  r a t h e r  th?"  
on t h e  d a t a .  For s p a t i a l  r e s o l u t i o n ,  we a r e  concerned about  f requency re- 
sponses  for i n t e r p o l a t i o n  k e r n e l s  and what e f fec t  they  may have on a p p l i c a -  
t i o n s .  For g e o r e f e r e n c i n g  and c a t a l o g i n g ,  i f  one c a n ' t  f i n d  t h e  d a t a ,  i t  
d o e s n ' t  do one much good. Ceoreferenc ing  s imply s a y s  t h a t  i f  we can r e g i s t e r  
any given set o f  d a t a  t o  a r e f e r e n c e  (1'11 c a l l  it a g r i d ) ,  t h e n ,  i m p l i c i t l y ,  
v a r i o u s  d a t a  s e t s  a r e  "more o r  less" r e g i s t e r e d  t o  each o t h e r  and p a r t  of t h a t  
more o r  less is what we want t o  t a l k  about  i n  t h i s  workshop and pane l  ses- 
s i o n s .  What we're t r y i n g  t o  d o  i s  make t h e  d a t a  c o r r e c t ,  make d a t a  se ts  corn- 
p a t i b l e  so they  can be used t o g e t h e r ,  and e v e n t u a l l y  make them a v a i l a b l e .  
which means p u t  them i n  such  a c o n d i t i o n  t h a t  wherc we c a l l  f o r  them from t h e  
a r c h i v e s ,  we g e t  can g e t  t h e  d a t a  back f a i r l y  expedic ious ly .  
Now t h e  n e t  r e s u l t :  t h e  n e t  u s e  of t h e  d a t a  i n  t h e  long  run is  e x t r a c t i o n  o f  
i n fo rma t ion .  Most or' t h e  models which a r e  now be ing  developed r e q u i r e d  d a t a  
from numerous d a t a  se ts .  One example of t h e  p o t e n t i a l  i n t e r p l a y  o f  se ts  o f  
d a t a  from v a r i o u s  s o u r c e s  i s  i l l u s t r a t d  i n  F i g u r e  2,  which i n d i c a t e s  some o f  
t h e  i n t e r p l a y s  betwezn d a t a  f o r  a p a r t i c u l a r  problem having t o  do  w i t h  weather  
q u e s t i o n s .  I d o n ' t  expec t  t o  go through t h i s  i l l u s t r a t i o n  i r  d e t a i l  except  t o  
i n d i c a t e  t h a t  there a r e  a l o t  o f  c r o s s i n g  arrows and many p a r t i c u l a r  processes 
t h a t  have t o  be modeled i n  scilving t h e  users informat ion  e x t r a c t i o n  problem. 
#Edited o r a l  p r e s e n t a t i o n .  
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https://ntrs.nasa.gov/search.jsp?R=19820020824 2020-03-21T08:02:12+00:00Z
T h i s  c a l l s  for d a t a  from v a r i o u s  s o u r c e s  i n  o r d e r  t o  allow m u l t i p l e  u s e r s  t o  
e x p e d i t i o u s l y  do t h e i r  problem s o l v i n g .  
Use of v a r i o u s  d a t a  sets t o g e t h e r  is one t h i n g ,  u s i n g  d a t a  sets t s g e t h e r  w i t h  
d a t a  from other s o u r c e s  such  a s  maps, or producing d a t a  i n  which t h e  r e q u i r e d  
o u t p u t  in format ion  is m a p r e l a t e d  is a n o t h e r .  What's involved b a s i c a l l y ,  is 
to  produce a d a t a  set i n  which t h e  i n d i v i u a l  d a t a  items i n  one  form of geo- 
g r a p h i c  coding a r e  i m p l i c i t l y  r e l a t e d  t o  a g i v e n  p o s i t i o n  on t h e  ground, be- 
cause  we have d e f i n e d  where t h a  etitire image m a t r i x  l i e s  on t h e  ground. Thus 
we can  c o n v e r t  l a t i t u d e  and l o n g i t u d e  i n t o  3 l i n e  and p i x e l  i n  t h e  d a t a  se t .  
I n  a d d i t i o n  t o  t h 3  q u e s t i o n  of u s i n g  d a t a  sets from v a r i o u s  s o u r c e s  t h e r e  is a 
g e n e r a l  q u e s t i o n  of being a b l e  t o  p u t  i t  i n t o  t h e  a r c h i v e s  and g e t  i t  o u t  o f  
t h e  a r c h i v e s  i n  a g e o g r a p h i c a l l y  coded s e n s e ,  so t h a t  we can begin  t o  produce 
d a t a  i n  a form t h a t  w i l l  make t h a t  whole p r o c e s s  f a l r l y  e x p e d i t i o u s .  
The requi rements  involved t h e  removal o f  d i s t o r t i o n s  and t h e n  p l a c i n g  of t h a t  
rect i f ied d a t a  i n  an a r c h i v e  A e r e  we can  r e t r i e v e  it; p l a c i n g  rectified d a t a  
on the  ground i n  a g i v e n  l o c a t i o n  is reviewed i n  Table  1. This is n o t  sup- 
posed t o  b e  a d e f i n a t i v e  l i s t ,  b u t  a l i t t l e  t a b l e  of some o f  t h e  s o u r c e s  of 
geometr ic  d i s t o r t i o n .  Many of t h e  items which a r e  inc luded  i n  t h e  table  and 
and f i g u r e s  a r e  going t o  be s u b j e c t s  o f  t h e  pane l  d i s c u s s i o n s .  What I want 
you t o  t h i n k  aboiit is t h e  f a c t  t h a t  t h e r e  are a number of c a u s e s  of d i s t o r -  
t i o n :  some of them i n  t h e  s e n s o r  i t?? '?,  some of them i n  t h e  s p a c e c r a f t  i n  
terms of  its p o i n t i n g ,  and some of them which are imp .:it i n  a remote s e n s i n g  
system !such a s  t h e  f a c t  t h n t  t h e  e a r t h  is round).  And it  may well be u s e f u l  
i n  your panel  d i s c u s s i o n s  t o  c o n s i d e r  t h e  sequence of c a u s e s  of d i s t o r t i o n s  
and d e c i d e  whether or n o t  t h a t  sequeace of c a u s e s  of d i s t o r t i o n s  g i v e s  you any 
c l u e s  a s  t o  t h e  sequence t o  remove t h e  d i s t o r t i o n s  and what might be  done i n  
t h a t  process .  Depending on which t y p e s  o f  d i s t o r t i o n s  you a r e  faced w i t h  you 
may t reat  them d i f f e r e n t l y .  Again t h e s e  t y p e s  of items and t h e i r  s p e c i f i c s  
are t h e  k i n d s  of t h i n g s  t h a t  you w i l l  be d i s c u s s i n g  i n  t h e  pane l  meetings.  
There a r e  3 series of problems involved i n  a t t e m p t i n g  t o  match one interest to  
t h e  other: I won't t r y  t o  go through t h o s e  because you have a set of q u e s t i o n s  
which h a s  been o u t l i n e d  for t h e  v a r i o u s  p a n e l s  a s  a guide  t o  th ink ing .  I do 
have F i g u r e  3, which w i l l  i n d i c a t e  t h e  t y p e  o f  problem we a r e  involved w i t h  i n  
doing t h e  c o r r e l a t i o n  of images t o  maps. Some of you may be f a m i l i a r  w i t h  
t h i s  pronesz,  and some o f  you may n o t ,  so 1'11 i n d i c a t e  i t  b r i e f l y .  We a r e  
t r y i n g  t o  f i n d  a p i e c e  o f  an image and i t 's  l o c a t i o n  w i t h  r e s p e c t  t o  a map. 
We t a k e  each p i e c e  of an image c o n t r o l  p o i n t  a r e a ,  t a k i n g  a series of those 
t h a t  a r e  scattered around t h e  f a c e  o f  a t o t a l  frame, then  t h a t  series of ties 
between l i n e  and p i x e l  and t h e  l o c a t i o n  on t h e  ground ( l a t i t u d e  and l o n g i t u d e )  
g i v e s  you t h e  d a t a  you need t o  d o  e geometr ica l  warping o f  t h e  image, so t h a t  
when you complete t h e  dewarping p r o c e s s ,  you now have an image whfch can l a y  
oil t h e  ground -- h o p e f u l l y  wi th  a l l  p i i t e l s  r e g i s t e r e d .  The essence  of t h e  
p r o c e s s  simply i s  t h a t  maps and images d o  n o t  c r o s s - c o r r e l a t e  very  n e a t l y  i n  a 
computer,  as maps and f e a t u r e s  i n  images look d i f f e r e n t .  We've g o t  a real 
problem i n  t r y i n g  t o  d e f i n e  a way t o  d o  t h a t  c o r r e l a t i o n .  The way i t  is cur-  
r e n t l y  being done is  t o  o p t i c a l l y  c o r r e l a t e ,  t h a t  is o p t i c a l l y  m i x  and over-  
l a y ,  and s h u f f l e  around u n t i l  t h e y  match, a d i g i t a l  d i s p l a y  o f  a s m a l l  p i e c e  
of image and 9 p i e c e  of a map. When t h o s e  two a r e  o p t i c a l l y  mixed ,  t hen  a 
surveyed p o i n t  on t h e  map cat1 be l o c a t e d  in t h e  sma l l  p i e c e  of v i s u a l  image by 
running a d i g i t a l  c u r s o r  around on t h e  d i s p l a y  u n t i l  it o v e r l a y s  t h e  p a r t i c u -  
l a r  ground c m t r o l  surveyed p o i n t .  The computer would know where t h e  c u r s o r  
1 4  
is i n  line and p i x e l  c c o r d i n a t e s ,  and y o u ' l l  t e l l  it i n  l a t i t u d e  and l o n g i t u d e  
where it is on t h e  map. That  g i v e s  you a t i e  between t h i s  l i t t l e  p i e c e  of i m -  
age, which i n  t h e  NASA pa r l ance  is a ground control  p o i n t  c h i p ,  and t h e  
ground. We know from t h e  geometry of t h e  g e n e r a l  s i t u a t i o n  approximate ly  
wirere th, is i n  t h e  incoming frame, so we p u l l  o u t  a l a r g e  p i e c e  of t h e  i n -  
coming frame d i g i t a l l : - ,  and we know from whence we got it. Now H e  have two 
images. Those can  be  c ros s -co r re l a t ed  i n  a computer more or  less a c c u r a t e l y ,  
and since we know t h e  p o s i t i o n  of  t h e  surveyed benchmark i n  t h e  l i t t l e  p i e c e  
of image, we can de termine  through cross-correlation t h e  p o s i t i o n  of each lit- 
t l e  p i e c e  w i t h i n  t h e  l a r g e  incoming image t o  t i e  t h e  l a r g e  incoming image's 
l ine  and p ixe l  w i t h  l a t i t u d e  and l o n g i t u d e .  We have t h e  t r a n s f e r  d a t a  now t o  
t a k e  t h a t  in to  t h e  t o t a l  frame domain, t i e  i n d i v i d u a l  ground c o n t r o l  p o i n t s  t o  
t h e  ground, and develop  t h e  e q u a t i o n s  needed for t h e  e n t i r e  image. Tha t ' s  t h e  
kind of p rocess  we' c u r r e n t l y  go through.  It r e q u i r e s  b u i l d i n g  a l i b r a r y  of 
ground control p o i n t s  ahead of time, so when t h e  incoming frames come we can  
d o  t h i s  c r o s s - c o r r e l a t i o n  e x p e d i t i o u s l y  on t h e  way through t h e  system, two- 
hundred frames a day. Anything t h a t  people  can t h i n k  of d u r i n g  t h e  workshop 
to  improve t h e  p rocess  w i l l  be apprec i a t ed .  
The p r o c e s s  t h a t  I desc r ibed  for  ground c o n t r o l  p o i n t s  r e q u i r e s  t h a t  t h a t  par-  
t i c u l a r  c o n t r o l  p o i n t  be known i n  x ,  y ,  and z a l t i t u d e ,  and t h e  b a s i c  dewarp- 
i n g  is normally a p rocess  of f i t t i n g  a b e s t - f i t  platre through t h a t  set  of 
ground c o n t r o l  p o i n t s .  T h a t ' s  f i n e ,  b u t ,  as you know, i n  h i l l y  coun t ry  t h e r e  
a r e  i n t e r m e d i a t e  p o i n t s  i n  t h e  image, which may o r  may n o t  b e  on t h a t  same 
plane.  If you have h i l l s  or v a l l e y s  i n  between, t h e y  a r e  going t o  be  d i s -  
p laced  by a d i s t a n c e  which is a func t ion  of t h e  a n g l e  from which you a re  view- 
i n g  t h o s e  p a r t i c u l a r  p o i n t s ,  i .e . ,  t h e  re l ief  d isp lacement  q u e s t i o n .  I worked 
up a l i t t l e  graph ( F i g u r e  4) which shows t h a t  relief d isp lacement  is  l a r g e r  
than  you l i k e  t o  b e l i e v e  when you are d e a l i n g  wi th  p i x e l s  of t h e  Thematic Map- 
p e r  s ize .  I n  p a r t i c u l a r ,  a l t hough  a r e p e a t  v i s i t  ove r  a g iven  a r e a  on t h e  
ground is in tended  t o  b e  a new image from p r e c i s e l y  t h e  same p o i n t ,  i n  prac- 
t i c e  t h a t  would n o t  be t r u e .  It  w i l l  be  from some o t h e r  p o i n t  nesrby.  And 
t h e  ques t ion  i s  how bad does  t h a t  s l i g h t  d i sp lacement  d i s p l a c e  p i e c e s  of  t h e  
image which a r e  n o t  on t h e  same b e s t  f i t  p lane .  Well, h e r e  is t h e  riet r e s u l t  
when you s c a l e  t h e  Thematic Mapper p i x e l s .  I t  s a y s ,  t h a t  wi th  a s u r p r i s i n g l y  
s m a l l  d i f f e r e n c e  i n  e l e v a t i o n  between a g iven  loca l  p o i n t  and t h e  b e s t  f i t  
p l a n e ,  wi th  a s u r p r i s i n g l y  s m a l l  s e p a r a t i o n  of t h e  two vantage  p o i n t s  (and re- 
membering t h a t  t h e  s c a t t e r  of r e p e a t  v i s i t s  on a g iven  p o i n t  is i n  t h e  neigh-  
borhood of 5-10 krn), t h e r e  i s  a f a i r l y  l a r g e  d isp lacement  p o t e n t i a l l y  of pix- 
e l s  which a r e  not  on t h a t  o r i g i n a l  p lane .  Even though you ha-e a good f i t  t o  
normal c o n t r o l  p o i n t s ,  you may or may n o t  have some o t h e r  problems i n  a r e a s  of 
high re l ief .  In  p a r t i c u l a r  wi th  Landsat ,  t h e  o v e r l a p  a r e a  from s i d e  t o  s i d e  
is a 170-km l i n e  of d isp lacement  between t h e  wings of  pa raove r l ap  images from 
a d j a c e n t  t r a c k s .  We a r e  going t o  ge t  a f a i r  amount of d isp lacement  d i s t o r t i o n  
due  t o  e l e v a t i o n  a l o n e .  
While t h e r e  a r e  a number of  o t h e r  items which we could t a l k  a b o u t ,  I t h i n k  
t h a t  is  enough t o  g i v e  you t h e  f l a v o r  of t h e  k i n d s  of problems t h a t  we see 
coming up: p o t e n t i a l  a r e a s  o f  d i s t o r t i o n ,  p o t e n t i a l  a r e a s  o f  l a c k  of r c g i s -  
t r a t i o n  of t h e  :mages t o  the ground. There a r e  a number of s p e c i f i c  q u e s t i o n s  
which nave been o u t l i n e d  f o r  t h e  va r ious  i n d i v i d u a l  p a n e l s  and you w i l l  g e t  
your c rack  a t  t h i n k i n g  about  t h e s e  and some of t h e  o t h e r  t o p i c s  a s  you g e t  i n -  
t o  t h e  panel  d i scuss ion .  
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LIBRARY 
BtHCH MARK 
CORRELATION FOR CONTROL POINT LOCATiON BY CONVOLUTION 
-SMALL AREA WHOSE LOCAT 
IS DESIRED IN INCOMIIJG 
FRAME. 
LARGE AREA FROM INCOMING 
CATION OF BENCH MARK IS 
DESIRED 
FRAME IN WHICH IDENTIFI- 
SMALL AREA MOVED OVER 
FIELD OF LAAGE AREA 
AND IXGREF OF hlATCH 
NED AT EACH POINT : 
(CORR, -A-IONJ DETERMI- 
POINT OF nwx CORRELATION 
I S  LOCA I ION 
Figure 3. Ground Control Point Operations 
* /  
oc 
0‘ 
c 


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