[gdal-dev] Call for discussion on "RFC 45: GDAL datasets and raster bands as virtual memory mappings"

[Even Rouault]

Hi,

This is a call for discussion for "RFC 45: GDAL datasets and raster bands as 
virtual memory mappings"

Beginning of the RFC inline (the full RFC includes a few colorful schemas !) :

"""

== Summary ==

This document proposes additions to GDAL so that image data of GDAL datasets 
and
raster bands can be seen as virtual memory mappings, for hopefully simpler 
usage.

== Rationale ==

When one wants to read or write image data from/into a GDAL dataset or raster
band, one must use the RasterIO() interface for the regions of interest that
are read or written. For small images, the most convenient solution is usually
to read/write the whole image in a single request where the region of interest
is the full raster extent. For larger images, particularly when they do not
fit entirely in RAM, this is not possible, and if one wants to operate on the
whole image, one must use a windowing strategy to avoid memory issues : 
typically
by proceeding scanline (or group of scanlines) by scanline, or by blocks for 
tiled
images. This can make the writing of algorithms more complicated when they 
need
to access a neighbourhoud of pixels around each pixel of interest, since the 
size of this
extra window must be taken into account, leading to overlapping regions of
interests. Nothing that cannot be solved, but that requires some additional
thinking that distracts from the followed main purpose.

The proposed addition of this RFC is to make the image data appear as a single
array accessed with a pointer, without being limited by the size of RAM with
respect to the size of the dataset (excepted limitations imposed by the CPU
architecture and the operating system)

"""

Best regards,

Even

-- 
Geospatial professional services
http://even.rouault.free.fr/services.html