[gdal-dev] Map algebra

[Ari Jolma]

11.04.2016, 19:30, alex kirjoitti:
>
> The curse of dimensionality comes in at the point, where the above
> function is called. The method callback is a template function and it
> needs the datatype of each band that is given to it as an argument. (I
> see now that I have made also the above function a template function,
> which may not be needed).
>
> In the end, all you need to do that is type specific is to apply the function on the pixel (at least in many cases). Would it be an option to only make the pixel level function a template, rather than the block level function?

The block-level function is repeated for all methods mainly because 
there are a couple of things that would cause an unnecessary overhead if 
called at each pixel. First, the method return value, if any, is 
initialized at the first call. Second, if the method needs to iterate 
over the whole band several times, that requires initialization etc. 
which is best done at block level (at the beginning of a first and at 
the end of a last block).

Also the pixel level operation should be as fast as possible and thus a 
function call in itself would cause overhead - however, using inline 
function might help.

Ari