[postgis-users] Problem using ST_MapAlgebraExpr

Pierre Racine Pierre.Racine at sbf.ulaval.ca
Mon Feb 27 07:51:39 PST 2012

```Ho I see better now. My email was not showing your code.

You have to convert minVal & maxVal to text:

newrast := ST_MapAlgebraExpr(rast, '8BUI', 'CASE WHEN rast1 < 0 THEN null ELSE (((rast)-(' || minVal::float8 || '))/((' || maxVal::float8 || ')-(' || minVal::float8 || '))) END');

Pierre

> -----Original Message-----
> From: postgis-users-bounces at postgis.refractions.net [mailto:postgis-users-
> bounces at postgis.refractions.net] On Behalf Of DavidRA
> Sent: Monday, February 27, 2012 10:19 AM
> To: postgis-users at postgis.refractions.net
> Subject: Re: [postgis-users] Problem using ST_MapAlgebraExpr
>
> Hi, it's very simple, like any other normalization: we have some values (in this
> case, the values of each cell of the input raster) and want to tranform them into
> others between 0 and 1. The minimum value of the raster will be transformed as
> 0, and the maximum as 1. And the formula used is (cellValue -
> minValue)/(maxValue - minValue).
>
> An example for a 2x2 raster:
>
> -Input raster:
>
> 2 3
> 6 4
>
> -Output raster:
>
> 0 0'25
> 1 0'5
>
> I hope this is clear enough, else let me know and I'll try to be more especific.
> Thanks.
>
> --
> View this message in context: http://postgis.17.n6.nabble.com/Problem-using-
> ST-MapAlgebraExpr-tp4514561p4515113.html
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