BC_Slopes

Slopes For The Interior Of BC
.
Written by Vera Lindsay
Atmospheric Modeling Assistant. UNBC
November 1, 2004

Project Overview

Image of Study Area

The purpose of this project was to provide a statistic to Brenda Moore describing the properties of slope for the interior of BC. This statistic was to be used as validation for the creation of a theoretical terrain.

The area of interest was defined as including the following map sheets: 93 b,c,f,g,j,k,n, and o.

A data set including all these map sheets except for 93b had been compiled for a previous project: http://www.gis.unbc.ca/courses/geog499/projects/2004/vera_lindsay/index.html

Therefore, the analysis was done using this pre-existing data set, and the GIS which contained it, mainly GRASS (Geographic Resources Analysis Support System). The missing map sheet was provided by Scott Emmons, (Senior GIS Lab Instructor).

General Data Information (generated by r.info)

   Type of Map: raster              Number of Categories: 2826
   Data Type:    FCELL
   Rows:         26428
   Columns:      17147
   Total Cells: 453160916
      Projection: UTM (zone 10)
            N: 6429565.95    S: 5768869.1   Res: 25
            E: 585619.54    W: 156943.15   Res: 25
   Range of data:    min = 196 max = 2826

Image Info

Procedure:
The original data was imported into a pre-existing Albers workspace as such:
r.in.gdal -o input=/usr/local/work/TRIM/250KBCTrimDEM/093o/grd/tdem093o/w001001.adf output=BC_250K_093o title="BC 250K 093o"
(for full details on this step please refer to: http://www.gis.unbc.ca/courses/geog499/projects/2004/vera_lindsay/GrassDocumentation.html)

The map sheets were joined to create one continuous data set (coverage):
r.patch input=BC_250K_093c,BC_250K_093f,BC_250K_093k,BC_250K_093n,BC_250K_093o,BC_250K_093j,BC_250K_093g output=bcslop

Then, the coverage was reprojected into a UTM workspace so it would be compatible with the additional 93b sheet and also to allow for measurement in meters:
r.proj input=bcslop location=dtap2 dbase=/usr/local/work/vera output=bcslope-utm

The 93b map sheet was imported using the r.in.arc command
Import>Raster Map>ESRI ARC/INFO ASCII-GRID or
r.in.arc input= output=

Then r.patch was run again to goin 93b with bcslope-utm to create bcslope2.
Statistics of the distribution of slopes over the study area were produced using the r.stats command:
r.stats -acpn bc-utm-slope nsteps=20 output=bcslope20.stat
r.stats -acpn bc-utm-slope nsteps=50 output=bcslope50.stat

The nsteps variable for the above command can be set to any value between 1 and 255.

The above statistics were re-generated at a resolution of 500X500 m. The image was converted to a lower resolution through setting the north-south grid resolution and east-west grid ressolution to 500 in g.region.sh:
Region>Manage Region
(Grass performs all functions on the current region.)

Image Info:
The image at the top of the page is an enhanced version of bcslope2.
The enhancement process included the below commands which can be run as a script:
region=bc-utm-slope
dem=bcslope2
twenty=$dem.20x
shade=$dem.shade
rescale=$twenty.rescale

g.region raster=$region
shade.rel.sh altitude=45 azimuth=315 elevation=$dem

r.mapcalc $twenty=20*$shade
r.rescale input=$twenty output=$rescale to=1,255

For further details on the above enhancement procedure, location (workspace) set up,or general GRASS use, please read:
http://www.gis.unbc.ca/courses/geog499/projects/2004/vera_lindsay/GrassDocumentation.html
or
http://grass.itc.it/gdp/html_grass5/index.html