Difference between revisions of "Comparative Analysis of Cost Path Analysis In Grass GIS and ArcMap"
m (→Arc to GRASS) |
m (→Arc to GRASS) |
||
Line 140: | Line 140: | ||
==Arc to GRASS== |
==Arc to GRASS== |
||
− | v.in.ogr converts GDAL compatible vectors to |
+ | v.in.ogr converts GDAL compatible vectors to GRASS Vectors. This can be done using: |
− | |||
− | This can be done using: |
||
''v.in.ogr dsn=fileName.shp output=outputName'' |
''v.in.ogr dsn=fileName.shp output=outputName'' |
||
− | r.in.arc converts an ESRI Arc ascii raster GRID file into a |
+ | r.in.arc converts an ESRI Arc ascii raster GRID file into a GRASS compatible binary raster layer. |
==Interpolation== |
==Interpolation== |
Revision as of 20:23, 19 December 2013
Contents
Introduction
About The Tutorial
ArcMap
About ArcMap
ArcMap is the proprietary GIS Software of the company ESRI and is a popular commercial solution used by companies to perform spatial operations.
Setup and Data
Open ArcMap and create a new map layout, making sure to set the workspace to known folders.
The following data files used are:
- 1. littlered.shp - The start location of little red.
- 2. gramma.shp - End location Gramma's cottage.
- 3. landcover.shp - The land cover types present.
- 4. elevation.shp - Elevation points for the area.
- 5. AOI.shp - Area of interest polygon that defines study area.
Add all of the above layers to the data frame.
Interpolation
In order to obtain the slope factor we first need to create a Digital Elevation Model (DEM) from our elevation points.
The DEM will be interpolated using the Inverse Distance Weighting (IDW)method and will be created with 500 m resolution. This is obtained with ArcMap's IDW tool.
ArcToolBox/SpatialAnaylstTools/interpolation/IDW
The Z field is contained in the attribute elevation, the output cell size will be 500 m and variable search radius of 12 points (default value).
Figure :Screenshot of IDW Tool
Figure : Digital Elevation model of AOI from IDW Interpolation
Determining Slope
A Slope raster is created using the Slope tool of ArcToolbox, this will use the previously created DEM and give slope in percent rise with a z factor of 1. The result raster shows slope in percent from green to red where red is the maximum slope.
ArcToolBox/SpatialAnaylstTools/Surface/Slope
Figure : Slope Tool
Figure : Percent Slope of AOI
Polygon to Raster
The land cover polygon must be converted to raster in order for it to be used for cost anaysis. The type conversion is done using the Polygon to Raster tool in ArcToolbox where the raster value assigned will be based on the "type" field such that polygon value that overlaps the middle of each 500 m cell defines the land cover assigned.
ArcToolBox/ConversionTools/ToRaster/PolygontoRaster
Figure : Polygon To Raster Tool
Figure : Raster of Landcover
Cost Reclassification
Both the Slope Raster and Land cover raster must be reclassified with cost values based on the percent slope and land cover types respectively. As per the originally specified difficulty and likelihood of wolf factor outlined in the introduction above each raster is re-classed with the Reclassify tool. The reclassification will be based on the SOMETHING and Type fields for slope and land cover respectively. Cost is shown in the results over white to black where black is the maximum cost.
ArcToolBox/SpatialAnaylstTools/Reclass/Reclassify
Figure : Reclassify Tool with: Slope parameters, Land cover parameters
Figure : Raster of slope cost, Raster of land cover cost
Cost Distance
The Cost Distance raster tracks the cumulative cost of traveling from each cell to the source (destination). For this example the destination/source will be Gramma's cottage as denoted by a black point on each map below. We have the option of setting an output location for the back link raster or this can also be created independently using the back link tool as it will be required to calculate optimal cost path.
The cost distance raster shows cumulative cost from a given cell to the source by the cheapest path as determined by the input cost grid. The back link raster gives the direction of movement from each cell toward the source on the least cost path as determined by the cost grid.
ArcToolBox/SpatialAnaylstTools/Distance/CostDistance
Figure : Cost Distance Tool
Figure : Cost Distance and Backlink Raster of Slope Cost
Cost Path
The cost path analysis finds the least cost path between the destination(Little Red) and the source (Gramma's Cottage) based on the cost distance and back link rasters. The following cost path is based on the slope only example that has been demonstrated thus far. The cost path tool generates only the polyline path, this polyline has been laid over each of the slope cost distance and slope cost for comparison.
Figure : Cost Distance Tool
Figure : Cost path for Slope Factor overlaid on slope cost path, slope cost.
Multi-Cost Models
Cost can be calculated using combination models of more then one cost factor. Two ways this can be done is with additive or multiplicative model where two cost rasters are combined. This can be performed in ArcMap using the raster calculator on each of the determined cost rasters as follows:
- 1. Additive Model- slope_cost + landcover_cost
- 2. Multiplicative Model- slope_cost * landcover_cost
ArcToolBox/SpatialAnaylstTools/Reclass/Reclassify
Figure : Raster calculator to construct multiplicative, additive model.
Using these new cost rasters the cost distance, back link and finally cost paths can be determined. The resulting optimal cost paths have been included below overlaid on their determinate cost grids.
Figure : Raster optimal cost path overlaid on cost distance raster for multiplicative and additive cost model respectively.
GRASS GIS
About GRASS
Geographic Resources Analysis Support System
Intro to GRASS GIS
Setup and Data
Open ArcMap and create a new map layout, making sure to set the workspace to known folders.
The following data files used are:
- 1. littlered.shp - The start location of little red.
- 2. gramma.shp - End location Gramma's cottage.
- 3. landcover.shp - The land cover types present.
- 4. elevation.shp - Elevation points for the area.
- 5. AOI.shp - Area of interest polygon that defines study area.
Arc to GRASS
v.in.ogr converts GDAL compatible vectors to GRASS Vectors. This can be done using: v.in.ogr dsn=fileName.shp output=outputName
r.in.arc converts an ESRI Arc ascii raster GRID file into a GRASS compatible binary raster layer.