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Raster Analysis

Raster Analysis. Raster math Topography: Slope, aspect, contours Reclassify Raster / Vector Conversions Statistics: min, max, mean, std. dev. Local, Neighborhood, Zonal Histograms No Data / Null Value Issues Future: Distance (cost). Jim’s Secrets for Rasters.

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Raster Analysis

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  1. Raster Analysis • Raster math • Topography: Slope, aspect, contours • Reclassify • Raster / Vector Conversions • Statistics: min, max, mean, std. dev. • Local, Neighborhood, Zonal • Histograms • No Data / Null Value Issues • Future: • Distance (cost)

  2. Jim’s Secrets for Rasters • Keep the overall size of the rasters below 200 Meg • Use “Resample” to convert to relatively small “IMG” files (or GRIDS) • Data Management Tools -> Raster -> Raster Processing -> Resample • Watch “Results” for errors • Geoprocessing -> “Results” • Use “Task Manager” when Arc crashes

  3. Task Manager • Right Click on Menu Bar, “Start Task Manager” • “End Process” on all “Arc” processes

  4. Raster Statistics • Local • Operate on one pixel in each raster • Neighborhood (or Focal) • Operate on a few pixels around each pixel • Zonal • Collection of regions • Region is a contiguous area of the same pixel values • Global • Operate on the “whole” raster

  5. Local Stats • “Cell Statistics” computes stats on all the values for a pixel in a multi-band raster. • Example for “Sum”: Esri ArcGIS 10 Help

  6. Neighborhood (or Focal) • Result=Operation on pixels nearby Columns Rows

  7. Focal Statistics • Computes stats on pixels around an existing pixel • Example for Sum: Esri ArcGIS 10 Help

  8. Zonal Statistics • Computes statistics for defined regions (features) • Tools: • Zonal Statistics: • Outputs a raster (not sure of the value) • Zonal Statistics as Table: • Outputs a table • Used to compute all kinds of valuable things: • Percent land cover • Percent impervious cover • Percent water below a certain depth • Etc.

  9. Zonal Statistics Zone Layer Value layer Output layer (or table) Esri ArcGIS 10 Help

  10. Conditional Operator • Con(<condition>,<true>,<false>) • Given a raster “condition”: • Puts the true value where true and false value where false Con!

  11. Elevations over 3000 meters • Con("W100N40.DEM“>3000,0,1)

  12. Elevations over 3000 meters

  13. Issues with No Data

  14. Issues with Signed Data

  15. Convert Values to “No Data” SetNull("W100N40.DEM"==55537,"W100N40.DEM")

  16. Rasters Draw as “Solid” Color • Click on “Type:” and select “Minimum-Maximum” • ArcGIS will compute statistics

  17. Histograms

  18. Exporting Histograms

  19. Titles and Axis Labels!

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