comparing directional maps

Rahul RakshitRahul RakshitPhD CandidatePhD CandidateClark UniversityClark Universityrrakshit@clarku.edurrakshit@clarku.edu

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Major PointsMajor Points

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http://weather.gfc.state.ga.us/Maps 4

http://ipf.ov.ingv.it/MorphoVesuvio_file/Gallery/Ves_Gallery.htm 5

Location: Plum Island EcosystemsLocation: Plum Island Ecosystems

6Long Term Ecological Research (LTER) siteLong Term Ecological Research (LTER) site

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Queen’s Case

Rooks' Case

ArcGIS Aspect Values (Degrees)

Idris

i Asp

ect V

alue

s (D

egre

es)

Scatterplot: Resolution 30 mScatterplot: Resolution 30 m

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Issue in comparing directionsIssue in comparing directionsAspect is a circular variableAspect is a circular variable

All the Units are in DegreesAll the Units are in DegreesAll the Units are in DegreesAll the Units are in Degrees

360

90

180

270

5355

10

350

10

Direction

0

270

90

225

Direction

37

FineResolution

CoarseResolution

Magnitude

5Magnitude

6

2

7

2√2

2North

6

2√2

5resultant

37˚

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Vector Addition: To coarsen the resolutionVector Addition: To coarsen the resolution

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:9000

:9000

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Coarse Resolution Aspect Maps After Vector AdditionCoarse Resolution Aspect Maps After Vector Addition

Scatter Plots: X Axis ArcGIS – Y Axis IdrisiScatter Plots: X Axis ArcGIS – Y Axis Idrisi

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Resolution (m)

MAE

(Deg

rees

)Mean Absolute Error (MAE)Mean Absolute Error (MAE)Shows the average difference in directionShows the average difference in direction

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CoarseFine

n

iii yf

nMAE

1

1

MAE is the weighted average of absolute errors

Major PointsMajor Points

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For more information, please contact at : rrakshit@clarku.edu

To tackle other types of variables, read the following from www.clarku.edu/~rpontius:

– Pontius, Thontteh and Chen. 2006. Components of information for multiple resolution comparison between maps that share a real variable. Environmental and Ecological Statistics.

– Pontius and Cheuk. 2006. A generalized cross-tabulation matrix to compare soft-classified maps at multiple resolutions. International Journal of Geographical Information Science.

Rahul extends special thanks to: Prof. Robert Gilmore Pontius Jr. for the concept and advice in every step of this research.

Acknowledgements and Plugs Acknowledgements and Plugs

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CosSlope

SinSlope

*

*

tan 1

Aspect ArcGIS (Radians) Aspect Idrisi (Radians)

Cos (Aspect)Sin (Aspect) Cos (aspect)Sin (Aspect)

Slope (ArcGIS)

Slope * Sin Slope * Cos

Aggregate to coarser resolution

Vector Addition (ArcGIS)

Slope (Idrisi)

Slope * Sin Slope * Cos

Aggregate to coarser resolution

Vector Addition (Idrisi)

Scatter Plots at Coarser Resolutions

Study Area Mask

Mean Absolute Error (MAE)

Elevation

Coarse Angle(ArcGIS) Coarse Angle(Idrisi)

Coarse Angle Difference