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On 09/29/2012 10:16 PM, Luciano La Sala wrote:
<blockquote cite="mid:079201cd9e7f$502d8c90$f088a5b0$@com.ar"
type="cite">
<pre wrap="">Hello QGIS users!
My name is Luciano and I am a wildlife researcher from Argentina. I am
rather new to the world of QGIS, so I apologize in advance for any rather
basic question.
I have several shapefiles of Argentina which I am supposed to use to make a
risk map. These vector files include:
1- Country border (line)
2- Airports (points)
3- Rivers (lines)
4- Wetlands (polygons)
5- Roads (lines)
6- Poultry farms (points)
I rasterized each of the vector files and gave each the same, new size (3993
hight and 2393 width) to fit the entire country. </pre>
</blockquote>
<br>
The easiest way to do this, I think, is with the gdal_rasterize
command. You can set the '-burn' option to set a value for the
raster. (The same command exists in the QGIS Raster menu, but allows
only to choose an attrib column from the shapefile for the raster
cell values. Not a static value, as you want). So, from the command
line:<br>
<br>
gdal_raster -of GTiff -burn 1 -tr <target resolution> -te
<target extents> airports.shp airports.tif <br>
<br>
and so on for each of the shapefiles.<br>
<br>
<br>
<br>
<blockquote cite="mid:079201cd9e7f$502d8c90$f088a5b0$@com.ar"
type="cite">
<pre wrap="">
Then, on each of the six maps, cells should be made to take a value of 1 if
risk factor is present (road, city, airport, wetland, and so on) and 0
otherwise. All the rasters should then be combined into one unified map. It
is my understanding that this unified map can be made using different
approaches (e.g. addition, addition and weighting, pair-wise comparisons).
In ArcView 3.2 this is done with "map calculator" of the "spatial analysis"
extension. These procedures would give a map in raster format where color
intensity of the cells is associated with the risk present in the area.
Finally, one can apply a kernel smoothing to ease interpretation of the map.
So at this point my questions are:
1) How do I assign values of 0 or 1 to pixels on each raster image? I
believe I could use RasterCalc plugin, but I just can't find a way around
this.
2) Once the above step is solved, how do I combine all maps into one using
one of the mentioned procedures (e.g. addition)? </pre>
</blockquote>
<br>
Now load all six rasters into QGIS, and use the raster calculator to
combine them into one, summing (using the '+' operator) the values
in each cell.<br>
<br>
<blockquote cite="mid:079201cd9e7f$502d8c90$f088a5b0$@com.ar"
type="cite">
<pre wrap="">
Thank you in advance.
Luciano La Sala
Centro de Estudios Cuantitativos en Sanidad Animal (CECSA) - CONICET
Facultad de Ciencias Veterinarias - Casilda
Universidad Nacional de Rosario
Argentina
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</pre>
</blockquote>
<br>
<br>
<pre class="moz-signature" cols="72">--
Micha Silver
GIS Consultant, Arava Development Co.
<a class="moz-txt-link-freetext" href="http://www.surfaces.co.il">http://www.surfaces.co.il</a></pre>
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