Raster data

1
Lecture 6

• Raster data

2
Raster layers

• Its all cells

3
A matrix of cells
Column
Grid origin 0, 0
0
1
2
3
Grid cell 3, 6
4
5
6
Square cells
7
From Clarke
4
Resolution (cell size)

• ½ cell size 2x the space

5
Cell values

• Each cell has a value Integer, real number, or
  NoData
• Cells can store raw numbers (elevation,
  temperature, slope)
• 1200
• 1130
• 1000
• 990
• 430
• Or index values
• 1 water
• 2 land
• 3 road
• 4 building

1
1
1
1
1
4
4
4
1
2
1
2
2
4
4
4
1
1
1
3
3
3
3
3
1
1
2
2
2
2
2
3
2
2
1
2
2
2
2
3
4
4
2
1
2
2
2
3
8
4
3
2
1
1
2
3
3
3
3
2
2
2
1
1
From Clarke
6
Categories of raster data

• Continuous
• Elevation
• Rainfall
• Discrete
• Landuse
• Tree type
• Imagery
• Air photo
• Sateilte

Land
Water
Bridge
7
The mixed pixel problem
Winner takes all
Water dominates
Edges separate
W
G
G
W
G
E
W
G
W
W
W
G
W
E
G
W
W
G
W
G
G
E
E
G
W
W
G
From Clarke
8
Raster to vector conversion
Vector to raster back to vector
How can you improve these results?
From Clarke
9
Raster overlay

• Cells from multiple layers
• Same location
• Like a shish kabob
• Write equations with maps as variables map
  algebra

Value in layer 1 Value in layer 2 Value in
layer 3 Value in layer 4
Rainfall 1998 10 Rainfall 1999
21 Rainfall 2000 9 Rainfall 2001 11
equals 51
10
Map algebra

• Use math operations , -, \, and
• Cells overlap each other
• Math performed on overlapping cells
• More or less rainfall?
• 7-43

7
9
2
5
8
3
6
-2
1
5
4
3
4
4
3
4
9
4
4
8
-1
3
0
0
3
-
5
6
4
4
5

6
1
9
4
5
2
1
1
1
2
4
0
8
3
3
3
3
6
3
1
0
1
1
4
7
3
2
5
-1
-6
6
5
1
1
1
0
0
0
5
5
-6
-5
1
-4
-4
Rain 1999
Rain 2000
Rain difference
11
Map algebra

• Logical operations (and, or)
• Cells overlap each other
• Fast math Its all Zeros and ones
• 1- good, 0 - bad
• Find best Ski areas

1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
0
0
1
0
0
1
1
1
0
0
0
0

AND
1
1
0
0
0
1
1
1
1
0
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Slope gt 15
No trees
12
Multiple rasters and transparency
13
Metadata

• Data about data
• Date information
• Who made it
• Location
• Scale
• Intended use
• Storage formats
• FGDC
• FAQ
• ISO
• XML

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TIN Triangulated Irregular Network

• 3D vector data
• Triangles
• More efficient than a grid

18
Elevations with TIN
19
3D Visualization
20
3D Visualization
21
World view zoom to Mt Everest
22
Raster data exercise