[postgis-devel] two-raster ST_MapAlgebraExpr specification discussion

[Pierre Racine]

> These specifications sacrifice two major things (consistency with PostGIS, and

The default behavior, when there is no alternative expression provided, is to set the resulting value to null when one of the overlapping value is null. So there is no conflict between this behavior and SELECT null + 4; = null

> the potential to extend beyond two rasters) 

Could you provided a SQL query involving 4 rasters for example? I think doing this exercise will make you realize that supporting processing on an array of raster stored in four different tables leads to impractical applications, too complex queries and uncertain processing time...

> and presumably you bought some
> functionality with this tradeoff. Can you outline what additional functionality
> you gained by this decision?

Being able to do map algebra over the union of two rasters is a very elegant and flexible way to merge two rasters considering all the possible way to blend them together. This allows us to implement very easily and quickly a long list of common functionality. We might want to optimize/reimplement some specific functions with time. We will see... I have been repeated this many times.

Again those conflicts are the only fruit of your imagination. They will vanish when you will spend more time trying things than writing long useless complaining emails... We really have other things to do. I'm not the only one thinking this...

So please be more practical and try before wasting our time in interminable divagations... I have been very patient since 6 months but now I'm tired. We wish you could bring real contribution (i.e. new practical coded functionalities) instead of mining our efforts.

Thanks,

Pierre