<s>
The	O
term	O
Digital	B-Application
Earth	I-Application
Reference	I-Application
Model	I-Application
(	O
DERM	O
)	O
was	O
coined	O
by	O
Tim	O
Foresman	O
in	O
context	O
with	O
a	O
vision	O
for	O
an	O
all	O
encompassing	O
geospatial	O
platform	O
as	O
an	O
abstract	O
for	O
information	O
flow	O
in	O
support	O
of	O
Al	O
Gore	O
's	O
vision	O
for	O
a	O
Digital	B-General_Concept
Earth	I-General_Concept
.	O
</s>
<s>
The	O
Digital	B-Application
Earth	I-Application
reference	I-Application
model	I-Application
seeks	O
to	O
facilitate	O
and	O
promote	O
the	O
use	O
of	O
georeferenced	O
information	O
from	O
multiple	O
sources	O
over	O
the	O
Internet	O
.	O
</s>
<s>
A	O
digital	B-Application
Earth	I-Application
reference	I-Application
model	I-Application
defines	O
a	O
fixed	O
global	O
reference	O
frame	O
for	O
the	O
Earth	O
using	O
four	O
principles	O
of	O
a	O
digital	B-General_Concept
system	O
,	O
namely	O
:	O
</s>
<s>
Data	O
acquisition	O
using	O
signal	O
processing	O
theory	O
(	O
sampling	B-Algorithm
and	O
quantizing	B-Algorithm
)	O
for	O
assigning	O
binary	O
values	O
from	O
continuous	O
analog	O
or	O
other	O
digital	B-General_Concept
sources	O
to	O
the	O
discrete	O
cell	O
partitions	O
;	O
</s>
<s>
A	O
set	O
of	O
mathematical	O
operations	O
built	O
on	O
the	O
indexing	O
for	O
algebraic	O
,	O
geometric	O
,	O
Boolean	O
and	O
image	B-Algorithm
processing	I-Algorithm
transforms	O
,	O
etc	O
.	O
</s>
<s>
The	O
distinction	O
between	O
"	O
digital	B-General_Concept
"	O
versus	O
"	O
analog	O
"	O
Earth	O
reference	O
model	O
is	O
made	O
in	O
the	O
manner	O
the	O
entire	O
Earth	O
surface	O
is	O
covered	O
.	O
</s>
<s>
Tessellation	B-Algorithm
refer	O
to	O
a	O
finite	O
number	O
of	O
objects/cells	O
that	O
cover	O
the	O
surface	O
as	O
discrete	O
partitions	O
while	O
Lattice	O
refer	O
to	O
ordered	O
sets	O
of	O
points	O
that	O
cover	O
the	O
surface	O
in	O
continuous	O
vector	O
space	O
.	O
</s>
<s>
The	O
mathematical	O
frame	O
for	O
a	O
digital	B-Application
Earth	I-Application
reference	I-Application
model	I-Application
is	O
a	O
tessellation	B-Algorithm
while	O
the	O
mathematical	O
frame	O
for	O
an	O
analog	O
Earth	O
reference	O
is	O
a	O
lattice	O
.	O
</s>
<s>
The	O
value	O
of	O
a	O
digital	B-Application
Earth	I-Application
reference	I-Application
model	I-Application
to	O
encode	O
information	O
about	O
the	O
Earth	O
is	O
akin	O
to	O
the	O
value	O
obtained	O
from	O
other	O
digital	B-General_Concept
technologies	O
,	O
namely	O
synchronization	O
of	O
the	O
physical	O
domain	O
with	O
the	O
information	O
domain	O
,	O
such	O
as	O
in	O
digital	B-General_Concept
audio	O
and	O
digital	B-Application
photography	I-Application
.	O
</s>
<s>
Data	O
reference	O
to	O
a	O
Digital	B-Application
Earth	I-Application
Reference	I-Application
Model	I-Application
(	O
DERM	O
)	O
becomes	O
ubiquitous	O
facilitating	O
distributed	O
spatial	O
queries	O
such	O
as	O
“	O
What	O
is	O
here	O
?	O
”	O
and	O
“	O
What	O
has	O
changed	O
?	O
”	O
.	O
</s>
<s>
Image	B-Algorithm
and	O
signal	O
processing	O
theory	O
can	O
be	O
utilized	O
to	O
operate	O
on	O
data	O
referenced	O
to	O
a	O
DERM	O
.	O
</s>
<s>
The	O
DERM	O
structure	O
is	O
data	O
independent	O
allowing	O
for	O
the	O
general	O
quantization	B-Algorithm
of	O
all	O
georeferenced	O
data	O
sources	O
onto	O
the	O
common	O
grid	O
.	O
</s>
<s>
Approaches	O
using	O
an	O
analog	O
reference	O
require	O
rigorous	O
manual	O
conflation	O
to	O
satisfy	O
the	O
creation	O
of	O
digital	B-General_Concept
products	O
such	O
as	O
digital	B-General_Concept
maps	O
or	O
other	O
cartographic	O
,	O
navigation	O
or	O
geospatial	O
information	O
(	O
see	O
also	O
GIS	B-Application
)	O
.	O
</s>
<s>
However	O
,	O
digital	B-General_Concept
models	O
are	O
weaker	O
at	O
geometric	O
transformations	O
where	O
translation	O
,	O
scaling	O
and	O
rotation	O
must	O
conform	O
to	O
the	O
discrete	O
cell	O
locations	O
wherein	O
on	O
an	O
analog	O
model	O
with	O
a	O
continuum	O
of	O
locations	O
geometric	O
transformation	O
are	O
straight	O
forward	O
with	O
no	O
requirements	O
for	O
reprocessing	O
or	O
resampling	O
.	O
</s>
<s>
As	O
rectilinear	O
structures	O
are	O
intuitive	O
but	O
lack	O
optimization	O
characteristics	O
as	O
a	O
tessellation	B-Algorithm
especially	O
when	O
tiled	O
to	O
a	O
sphere	O
,	O
other	O
schemes	O
including	O
voronoi	O
regions	O
,	O
peano	O
curves	O
,	O
triangles	O
and	O
hexagonal	O
tilings	O
have	O
been	O
advanced	O
as	O
superior	O
alternatives	O
.	O
</s>
<s>
Few	O
of	O
these	O
models	O
have	O
encompassed	O
a	O
complete	O
digital	B-Application
Earth	I-Application
reference	I-Application
model	I-Application
where	O
both	O
a	O
formation	O
of	O
digits	O
that	O
represent	O
a	O
hierarchy	O
where	O
the	O
index	O
contains	O
a	O
parent	O
child	O
relationship	O
and	O
a	O
formation	O
of	O
digits	O
that	O
monotonically	O
converges	O
by	O
a	O
set	O
modulus	O
to	O
all	O
vector	O
Reals	O
.	O
</s>
<s>
The	O
International	O
Society	O
on	O
Digital	B-General_Concept
Earth	I-General_Concept
has	O
a	O
standing	O
committee	O
considering	O
DERM	O
implementations	O
and	O
standards	O
which	O
includes	O
both	O
the	O
Earth	O
reference	O
frame	O
and	O
the	O
ancillary	O
requirements	O
for	O
metadata	O
and	O
attribute	O
semantics	O
.	O
</s>
