<s>
Ground	B-General_Concept
truth	I-General_Concept
is	O
information	O
that	O
is	O
known	O
to	O
be	O
real	O
or	O
true	O
,	O
provided	O
by	O
direct	O
observation	O
and	O
measurement	O
(	O
i.e.	O
</s>
<s>
The	B-Application
Oxford	I-Application
English	I-Application
Dictionary	I-Application
(	O
s.v.	O
</s>
<s>
ground	B-General_Concept
truth	I-General_Concept
)	O
records	O
the	O
use	O
of	O
the	O
word	O
Groundtruth	O
in	O
the	O
sense	O
of	O
'	O
fundamental	O
truth	O
 '	O
from	O
Henry	O
Ellison	O
's	O
poem	O
"	O
The	O
Siberian	O
Exile	O
's	O
Tale	O
"	O
,	O
published	O
in	O
1833	O
.	O
</s>
<s>
"	O
Ground	B-General_Concept
truth	I-General_Concept
"	O
may	O
be	O
seen	O
as	O
a	O
conceptual	O
term	O
relative	O
to	O
the	O
knowledge	O
of	O
the	O
truth	O
concerning	O
a	O
specific	O
question	O
.	O
</s>
<s>
For	O
example	O
,	O
suppose	O
we	O
are	O
testing	O
a	O
stereo	B-Algorithm
vision	I-Algorithm
system	O
to	O
see	O
how	O
well	O
it	O
can	O
estimate	O
3D	O
positions	O
.	O
</s>
<s>
The	O
"	O
ground	B-General_Concept
truth	I-General_Concept
"	O
might	O
be	O
the	O
positions	O
given	O
by	O
a	O
laser	O
rangefinder	O
which	O
is	O
known	O
to	O
be	O
much	O
more	O
accurate	O
than	O
the	O
camera	O
system	O
.	O
</s>
<s>
Bayesian	B-Application
spam	I-Application
filtering	I-Application
is	O
a	O
common	O
example	O
of	O
supervised	O
learning	O
.	O
</s>
<s>
This	O
depends	O
on	O
the	O
ground	B-General_Concept
truth	I-General_Concept
of	O
the	O
messages	O
used	O
to	O
train	O
the	O
algorithm	O
inaccuracies	O
in	O
the	O
ground	B-General_Concept
truth	I-General_Concept
will	O
correlate	O
to	O
inaccuracies	O
in	O
the	O
resulting	O
spam/non	O
-spam	O
verdicts	O
.	O
</s>
<s>
In	O
remote	B-Application
sensing	I-Application
,	O
"	O
ground	B-General_Concept
truth	I-General_Concept
"	O
refers	O
to	O
information	O
collected	O
on	O
location	O
.	O
</s>
<s>
Ground	B-General_Concept
truth	I-General_Concept
allows	O
image	O
data	O
to	O
be	O
related	O
to	O
real	O
features	O
and	O
materials	O
on	O
the	O
ground	O
.	O
</s>
<s>
The	O
collection	O
of	O
ground	B-General_Concept
truth	I-General_Concept
data	O
enables	O
calibration	B-General_Concept
of	O
remote-sensing	B-Application
data	O
,	O
and	O
aids	O
in	O
the	O
interpretation	O
and	O
analysis	O
of	O
what	O
is	O
being	O
sensed	O
.	O
</s>
<s>
Examples	O
include	O
cartography	O
,	O
meteorology	O
,	O
analysis	O
of	O
aerial	O
photographs	O
,	O
satellite	B-Application
imagery	O
and	O
other	O
techniques	O
in	O
which	O
data	O
are	O
gathered	O
at	O
a	O
distance	O
.	O
</s>
<s>
More	O
specifically	O
,	O
ground	B-General_Concept
truth	I-General_Concept
may	O
refer	O
to	O
a	O
process	O
in	O
which	O
a	O
"	O
pixel	B-Algorithm
"	O
on	O
a	O
satellite	B-Application
image	O
is	O
compared	O
to	O
what	O
is	O
there	O
in	O
reality	O
(	O
at	O
the	O
present	O
time	O
)	O
in	O
order	O
to	O
verify	O
the	O
contents	O
of	O
the	O
"	O
pixel	B-Algorithm
"	O
on	O
the	O
image	O
(	O
noting	O
that	O
the	O
concept	O
of	O
a	O
"	O
pixel	B-Algorithm
"	O
is	O
somewhat	O
ill-defined	O
)	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
a	O
classified	O
image	O
,	O
it	O
allows	O
supervised	O
classification	O
to	O
help	O
determine	O
the	O
accuracy	O
of	O
the	O
classification	O
performed	O
by	O
the	O
remote	B-Application
sensing	I-Application
software	O
and	O
therefore	O
minimize	O
errors	O
in	O
the	O
classification	O
such	O
as	O
errors	O
of	O
commission	O
and	O
errors	O
of	O
omission	O
.	O
</s>
<s>
Ground	B-General_Concept
truth	I-General_Concept
is	O
usually	O
done	O
on	O
site	O
,	O
performing	O
surface	O
observations	O
and	O
measurements	O
of	O
various	O
properties	O
of	O
the	O
features	O
of	O
the	O
ground	O
resolution	O
cells	O
that	O
are	O
being	O
studied	O
on	O
the	O
remotely	O
sensed	O
digital	O
image	O
.	O
</s>
<s>
It	O
also	O
involves	O
taking	O
geographic	O
coordinates	O
of	O
the	O
ground	O
resolution	O
cell	O
with	O
GPS	O
technology	O
and	O
comparing	O
those	O
with	O
the	O
coordinates	O
of	O
the	O
"	O
pixel	B-Algorithm
"	O
being	O
studied	O
provided	O
by	O
the	O
remote	B-Application
sensing	I-Application
software	O
to	O
understand	O
and	O
analyze	O
the	O
location	O
errors	O
and	O
how	O
it	O
may	O
affect	O
a	O
particular	O
study	O
.	O
</s>
<s>
Ground	B-General_Concept
truth	I-General_Concept
is	O
important	O
in	O
the	O
initial	O
supervised	O
classification	O
of	O
an	O
image	O
.	O
</s>
<s>
The	O
spectral	O
characteristics	O
of	O
these	O
areas	O
are	O
used	O
to	O
train	O
the	O
remote	B-Application
sensing	I-Application
software	O
using	O
decision	O
rules	O
for	O
classifying	O
the	O
rest	O
of	O
the	O
image	O
.	O
</s>
<s>
Additional	O
ground	B-General_Concept
truth	I-General_Concept
sites	O
allow	O
the	O
remote	B-Application
sensor	I-Application
to	O
establish	O
an	O
error	O
matrix	O
that	O
validates	O
the	O
accuracy	O
of	O
the	O
classification	O
method	O
used	O
.	O
</s>
<s>
It	O
is	O
important	O
that	O
the	O
remote	B-Application
sensor	I-Application
chooses	O
a	O
classification	O
method	O
that	O
works	O
best	O
with	O
the	O
number	O
of	O
classifications	O
used	O
while	O
providing	O
the	O
least	O
amount	O
of	O
error	O
.	O
</s>
<s>
Ground	B-General_Concept
truth	I-General_Concept
also	O
helps	O
with	O
atmospheric	O
correction	O
.	O
</s>
<s>
Since	O
images	O
from	O
satellites	B-Application
obviously	O
have	O
to	O
pass	O
through	O
the	O
atmosphere	O
,	O
they	O
can	O
get	O
distorted	O
because	O
of	O
absorption	O
in	O
the	O
atmosphere	O
.	O
</s>
<s>
So	O
ground	B-General_Concept
truth	I-General_Concept
can	O
help	O
fully	O
identify	O
objects	O
in	O
satellite	B-Application
photos	O
.	O
</s>
<s>
An	O
example	O
of	O
an	O
error	O
of	O
commission	O
is	O
when	O
a	O
pixel	B-Algorithm
reports	O
the	O
presence	O
of	O
a	O
feature	O
(	O
such	O
as	O
trees	O
)	O
that	O
,	O
in	O
reality	O
,	O
is	O
absent	O
(	O
no	O
trees	O
are	O
actually	O
present	O
)	O
.	O
</s>
<s>
Ground	O
truthing	O
ensures	O
that	O
the	O
error	O
matrices	O
have	O
a	O
higher	O
accuracy	O
percentage	O
than	O
would	O
be	O
the	O
case	O
if	O
no	O
pixels	B-Algorithm
were	O
ground-truthed	O
.	O
</s>
<s>
An	O
example	O
of	O
an	O
error	O
of	O
omission	O
is	O
when	O
pixels	B-Algorithm
of	O
a	O
certain	O
thing	O
,	O
for	O
example	O
,	O
maple	O
trees	O
,	O
are	O
not	O
classified	O
as	O
maple	O
trees	O
.	O
</s>
<s>
The	O
process	O
of	O
ground-truthing	O
helps	O
to	O
ensure	O
that	O
the	O
pixel	B-Algorithm
is	O
classified	O
correctly	O
and	O
the	O
error	O
matrices	O
are	O
more	O
accurate	O
.	O
</s>
<s>
In	O
GIS	B-Application
the	O
spatial	O
data	O
is	O
modeled	O
as	O
field	O
(	O
like	O
in	O
remote	B-Application
sensing	I-Application
raster	O
images	O
)	O
or	O
as	O
object	O
(	O
like	O
in	O
vectorial	B-Application
map	I-Application
representation	O
)	O
.	O
</s>
<s>
Geographic	B-Application
information	I-Application
systems	I-Application
such	O
as	O
GIS	B-Application
,	O
GPS	O
,	O
and	O
GNSS	O
,	O
have	O
become	O
so	O
widespread	O
that	O
the	O
term	O
"	O
ground	B-General_Concept
truth	I-General_Concept
"	O
has	O
taken	O
on	O
special	O
meaning	O
in	O
that	O
context	O
.	O
</s>
<s>
If	O
the	O
location	O
coordinates	O
returned	O
by	O
a	O
location	O
method	O
such	O
as	O
GPS	O
are	O
an	O
estimate	O
of	O
a	O
location	O
,	O
then	O
the	O
"	O
ground	B-General_Concept
truth	I-General_Concept
"	O
is	O
the	O
actual	O
location	O
on	O
Earth	O
.	O
</s>
<s>
The	O
ground	B-General_Concept
truth	I-General_Concept
being	O
estimated	O
by	O
those	O
coordinates	O
is	O
the	O
tip	O
of	O
George	O
Washington	O
's	O
nose	O
on	O
Mount	O
Rushmore	O
.	O
</s>
<s>
The	O
accuracy	O
of	O
the	O
estimate	O
is	O
the	O
maximum	O
distance	O
between	O
the	O
location	O
coordinates	O
and	O
the	O
ground	B-General_Concept
truth	I-General_Concept
.	O
</s>
<s>
We	O
could	O
say	O
in	O
this	O
case	O
that	O
the	O
estimate	O
accuracy	O
is	O
10	O
meters	O
,	O
meaning	O
that	O
the	O
point	O
on	O
earth	O
represented	O
by	O
the	O
location	O
coordinates	O
is	O
thought	O
to	O
be	O
within	O
10	O
meters	O
of	O
George	O
's	O
nose	O
—	O
the	O
ground	B-General_Concept
truth	I-General_Concept
.	O
</s>
<s>
In	O
slang	O
,	O
the	O
coordinates	O
indicate	O
where	O
we	O
think	O
George	O
Washington	O
's	O
nose	O
is	O
located	O
,	O
and	O
the	O
ground	B-General_Concept
truth	I-General_Concept
is	O
where	O
it	O
really	O
is	O
.	O
</s>
<s>
In	O
practice	O
a	O
smart	O
phone	O
or	O
hand-held	O
GPS	O
unit	O
is	O
routinely	O
able	O
to	O
estimate	O
the	O
ground	B-General_Concept
truth	I-General_Concept
within	O
6	O
–	O
10	O
meters	O
.	O
</s>
<s>
US	O
military	O
slang	O
uses	O
"	O
ground	B-General_Concept
truth	I-General_Concept
"	O
to	O
refer	O
to	O
the	O
facts	O
comprising	O
a	O
tactical	O
situation	O
—	O
as	O
opposed	O
to	O
intelligence	O
reports	O
,	O
mission	O
plans	O
,	O
and	O
other	O
descriptions	O
reflecting	O
the	O
conative	O
or	O
policy-based	O
projections	O
of	O
the	O
industrial·military	O
complex	O
.	O
</s>
<s>
The	O
term	O
appears	O
in	O
the	O
title	O
of	O
the	O
Iraq	O
War	O
documentary	O
film	O
The	O
Ground	B-General_Concept
Truth	I-General_Concept
(	O
2006	O
)	O
,	O
and	O
also	O
in	O
military	O
publications	O
,	O
for	O
example	O
Stars	O
and	O
Stripes	O
saying	O
:	O
"	O
Stripes	O
decided	O
to	O
figure	O
out	O
what	O
the	O
ground	B-General_Concept
truth	I-General_Concept
was	O
in	O
Iraq.	O
"	O
</s>
