Transcript Maps by Computer – Part 2 GEOG 3530/8535 University of Nebraska at Omaha.

Maps by Computer – Part 2
GEOG 3530/8535
University of Nebraska at Omaha
Slivers
Digitizer
x coordinate
Accuracy: 0.001”
Repeatability: 0.003”
Impossible to hold
hand steady at that
degree of resolution.
y coordinate
Arc/Node Topology
Arc
1
2
3
4
5
6
7
8
Begin Node
I
II
III
V
III
IV
I
II
End Node
II
III
IV
I
V
V
IV
IV
Right Poly
A
B
C
B
B
D
D
A
Left Poly
0
0
0
0
C
C
A
B
Slivers make polygons
Simple Polygon
Arc/node Polygon
Expected 200 polygons
Conversion
After conversion, we had
over 10,000 polygons
Solution: Deleted smallest
polygons and merged with
surrounding polygon.
Merging Polygons
Redistricting – electoral, congressional
Coordinate Transformations
2x transformation
2,2 becomes 4,4
4,4 becomes 8,8
Rotation
u = cos (radang)
v = sin (radang)
for i = 1, n
tempx = x(i) * u + y(i) * v
y(i) = -x(i) * v + y(i) * u
x(i) = tempx
next i
Interpolation
What does squaring the distances do?
What would the value be if distances cubed?
Object Graphics - Illustrator
Coordinates
Raster Overlay
How many commercial/100 year flood pixels?
Overlay