[mapserver-users] Raster merge

[Andrew Mason]

Frank,

Thanks for that advice, a further complication is that I'd like to be  
able to specify the suitability values as part of the request.
Is there a way to apply some conditional processing based upon the  
value of request parameters?

Andrew


On 1 Jul 2008, at 13:45, Frank Warmerdam wrote:

> Andrew Mason wrote:
>> Hello List,
>> I wonder if anyone can anyone suggest a possible mechanism for  
>> achieving the following?
>> I have two rasters covering the same area.
>> Raster A contains the suitability of the location for the growth  
>> of Species A (on a scale of 1 to 30)
>> Raster B contains the suitability of the location for the growth  
>> of Species B (on a scale of 1 to 30)
>> I would like to generate a layer that shows the result of the  
>> following rule:
>> Display green at locations where Species A suitability is > 18
>> Otherwise if Species B suitability > 14 display blue
>> Otherwise display red.
>
> Andrew,
>
> I haven't tried this, but I think you could handle this with two  
> layers
> in your mapfile, one for each raster.  The first layer should be  
> for RasterB.
> It should have one class with an expression selecting suitability  
> values
> greater than 14 and a color of blue.  The next layer should be for  
> RasterA
> and have one class for suitabilities greater than 18 and a color of  
> green.
> It should also have a second class with no expression and a color  
> of red.
>
> There are some docs on raster classification in:
>
>   http://mapserver.gis.umn.edu/docs/howto/raster_data
>
> However, if RasterA and RasterB are not dynamic, you might consider
> producing the merged result as a preprocessing step instead of making
> MapServer do the computations for each map render.  It would be more
> efficient.  Such raster modelling could be done in GRASS, for  
> instance.
>
> Best regards,
> -- 
> --------------------------------------- 
> +--------------------------------------
> I set the clouds in motion - turn up   | Frank Warmerdam,  
> warmerdam at pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam
> and watch the world go round - Rush    | President OSGeo, http:// 
> osgeo.org
>