[R-sig-Geo] Mapping contours from jpg map

[Tomislav Hengl]

On 7/8/2011 9:33 AM, Johan Van de Wauw wrote:
> Apart from grass gis, you can also do this in saga gis, or run this
> through RSAGA. Since it seems you have to do this only once, it would
> be much easier to just use the GUI.
>
> 1) Open your shapefile
> 2) run the module grid\shapes to grid (choose a reasonable cell size)
> 3) run the module grid\close gaps (you now have a altitude grid)
> 4) run the module terrain analysis\morphometry\slope,aspect... (you
> now have a slope grid)
> 5) you could now overlay your points, or do that in R.

Or if you prefer coding ;)

 > rm(volcano)
 > volcano <- ContourLines2SLDF(contourLines(volcano))
 > volcano$altitude <- as.numeric(as.character(volcano$level))
 > writeLinesShape(volcano, "volcano.shp")

 > rsaga.get.usage(lib="grid_gridding", module=0)
# SAGA 2.0.7
library name:   grid_gridding
module name :   Shapes to Grid
# interpolate lines to rasters:
 > rsaga.geoprocessor(lib="grid_gridding", module=0, 
param=list(GRID="DEM.sgrd", INPUT="volcano.shp", FIELD=0, LINE_TYPE=0, 
USER_SIZE=10))
# close gaps with splines:
 > rsaga.geoprocessor(lib="grid_tools", module=7, 
param=list(INPUT="DEM.sgrd", RESULT="DEM.sgrd")) # write to the same file


for more examples see also

http://spatial-analyst.net/book/Geomorphmapping

http://geomorphometry.org/content/uncertainty-stream-networks-derived-elevation-data


T. Hengl
http://www.wewur.wur.nl/popups/vcard.aspx?id=HENGL001


>
> http://www.saga-gis.org
>
>
> Johan
>
> On Thu, Jul 7, 2011 at 6:25 PM, Sarah Papworth
> <sarah.papworth06 at imperial.ac.uk>  wrote:
>> Dear all,
>>
>> I have a jpg map of altitudinal contours in my study area which I
>> would like to map and use in R to calculate the altitude and slope of
>> GPS coordinates.
>> So far, I have painstakingly traced these contours in ArcMap to create
>> a shapefile (of polylines) with altitude. I have now imported this
>> file shapefile into R.
>>
>>   What I would like to do is turn it into a raster of slope and
>> altitude, but I can't seem to find any method of doing this in the
>> online R help archives. Does anyone have any idea which package I
>> should be using, or perhaps if it is even possible to turn this type
>> of shapefile into a raster?
>>
>> Thanks in advance!
>>
>> Sarah
>>
>>
>> --
>> Imperial College London
>> http://www.iccs.org.uk/sarahpapworth.htm
>>
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