[GRASS-user] "active window" Definition

Glynn Clements glynn at gclements.plus.com
Fri Jan 8 17:38:06 EST 2010

Franz Schiller wrote:

> While I was reading G_window_rows definition at GRASS6 programmers manual, I
> found this definition:
> Number of rows in active window.
> What does active window means? Because I can read number of rows/columns
> from raster header. I'm not real sure of what is active window.

The "window" specifies the relationship between row/column indices and
cartographic or geographic coordinates.

All raster processing is performed on the grid specified by the
window; all input maps are automatically resampled to it.

Unless the program explicitly sets a window, it will be initialised
based upon either:

1. The contents of the GRASS_REGION environment variable.

2. The contents of the named region specified by the WIND_OVERRIDE
environment variable.

3. The contents of the WIND file in the current mapset.

The most common case is #3.

Programs which explicitly set a window include r.resamp.interp,
r.resamp.stats and r.resamp.rst. These all set the window to match the
input map, so that they read the "raw" data without any resampling.

Glynn Clements <glynn at gclements.plus.com>

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