NACIS 2016 Presentation Patrick Kennelly, Long Island University Generalizing terrain representations using shaded relief are challenging, with previous efforts focusing on two methods. The first approach involves filtering or modifying the original terrain data to make a more generalized elevation model. The second approach involves filtering or generalizing the values of gray on the shaded relief map itself. An alternative approach presented here is to use surface normal vectors that are first resolved into x, y, and z components and then summed within the kernel of a low-pass filter. In this manner, the orientations of these vectors used in relief shading and associated surfaces are adjusted independently of the elevation value. Results appear sharper than generalized terrain models that are shaded or generalized shaded relief maps when a kernel of the same dimension is used to calculate mean values.

1. Generalizing Terrain
Representa0ons with Vector Sums
Patrick
Kennelly
Long
Island
University

2. Generalizing Terrain
Representa0ons with Vector Sums
• The
importance
of
generalizing
terrain
representa<ons
• Approaches
for
generalizing
relief
shading
• A
new
method
for
generalizing
relief
shading
in
vector
space

3. Approaches for Generalizing
Relief Shading
• Smooth
the
relief
shaded
map
• Smooth
the
terrain
then
relief
shade
• Smooth
the
surface
normal
vector
then
relief
shade

4. Smooth the Relief Shaded Map

5. Smooth the Relief Shaded Map

6. Smooth the Relief Shaded Map
15
x

7. mooth the Terrain then Relief Shad

8. mooth the Terrain then Relief Shad
15
x

9. mooth the Terrain then Relief Shad
z,
A.
M.,
Jenny,
B.,
&
Hurni,
L.
(2010).
Terrain
sculptor:
generalizing
odels
for
relief
shading.
Cartographic
Perspec/ves,
(67),
51-­‐60.

10. • Low-­‐pass
mean
filter
• Curvature
coefficients
to
iden<fy
valleys
and
ridges
• Ver<cally
exaggerate
and
deepen
smoothed
terrain
model
• Mountain
and
lowland
grids
create
with
weigh<ng
factors
applied
to
exaggerated/deepened
and
smoothed
grids
• Grids
recombined
with
smoothed
slope
grid
• Shaded
relief
created
from
recombined
grid
mooth the Terrain then Relief Shade
Terrain Sculptor

11. Smooth the Surface Normal Vector
then Relief Shade

12. Smooth the Surface Normal Vector
then Relief Shade

13. Smooth the Surface Normal Vector
then Relief Shade
15
x

21. Summary
A
low
pass
filter
employing
a
large
(15x15)
kernel
can
be
used
to
sum
surface
normal
vectors
in
a
manner
that
results
in
smoothed
relief
shaded
maps
Results
compare
with
hand-­‐drawn
methods
and
methods
sculp<ng
terrain
for
final
relief
shading
The
result
is
a
relief
shaded
map
-­‐
-­‐
no
analogous
smoothed
terrain
model
exists