nr 322: interpolation
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NR 322: Interpolation
Jim Graham
Fall 2008
Chapters 7 and 8
Interpolation
• Interpolation is a method of constructing new data points within the range of a discrete set of known data points.
Simple Interpolation
Mea
sure
d V
alue
s
Spatial Cross-section
50
3540
20
Simple Interpolation
Mea
sure
d V
alue
s
Spatial Cross-section
50
3540
20
Simple Interpolation
Mea
sure
d V
alue
s
Spatial Cross-section
50
3540
20
55 4247 36 36 37 38 40 34 28 21
Spline Interpolation
Mea
sure
d V
alue
s
Spatial Cross-section
50
3540
20
55 4248 35 35 37 38 40 36 28 22
First law of Geography
• Everything is related to everything else, but near things are more related than distant things
• TOBLER, W. R. (1970). "A computer movie simulating urban growth in the Detroit region". Economic Geography, 46(2): 234-240.
Process
• Obtain points with measurements
• Interpolate between the points using:– Inverse Distance Weighting– Kriging– Splines
• Convert the raster to vector using contours
Vector (Points) to Rater
• Interpolation– IDW– Kriging– Splines
• Density
Inverse Distance Weighting
• Points closer to the pixel have more “weight”
Spline
• Spline type: Tension
• Increase “Weight” or decrease the “Number of points”
Kriging
• See the Geostatistical Analyst
• NR/ST523 - Quantitative Spatial Analysis
• NR512 - Introduction to Spatial Statistical Modeling of Natural Resources
Geostatistical Analyst
• Provides much more control over interpolation
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