[Qgis-user] (Interpolate Plugin) Is it possible to set the opacity of grids which contain no points to 0%?

[Micha Silver]

On 10/29/2010 11:26 PM, Ryan Michael wrote:
> I have a data set that I'm trying to interpolate, and in some cases 
> there are large swaths of area that are surrounded by points, but 
> don't contain any points.  This produces a graph where these interior 
> regions have values determined by the nearest points.
>
> Rather than assuming that these points are accurately represented by 
> the surrounding points, I would prefer to not render those grid 
> points, and only show grid boxes which are actually representative of 
> data.  Is there a way to do this?  I was thinking I could add second 
> field and assign opacity to that, but I can't figure out a way to get 
> the field to be 'true' if there are points enclosed and 'false' 
> otherwise (or to simply count the number of enclosed points.)
>
> Any ideas?

Just a thought- You might create a buffer around all points at the max 
distance you consider to be relevant for interpolation. The buffer will 
thus cover only areas with a density of points of your choosing. The 
"swaths" will be outside the buffer. Convert the buffer to a raster, and 
make it a MASK. Now, after doing your point interpolation, use the mask 
to set to null all the areas outside the buffer.

>
> Thanks for any suggestions!
>
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-- 
Micha Silver
Arava Development Co. +972-52-3665918
http://www.surfaces.co.il


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