Doubts confirmed... Circles in r.le.setup may not reach the expected
size. For instance, using the option 'sampling units centered over
sites', if I take a 25.5 cells radius everything works fine (I get a
total of 2053 pixels in each sampling units, which looks reasonable
25.5^2 * pi = 2042.8), but if I want a larger sampling unit of 125.5
pixel radius, I get a warning asking confirmation whether I want a
radius > 100 pixels, and then get a total area of 2601 pixels, which is
far below what is expected from a 125.5 radius (125.5^2 * pi = 49480.87).
The pixel size is 4 m in reality, and the two radius correspond to appx
100m and 500m...
Any hint welcome !
Patrick
Patrick Giraudoux wrote:
Sorry to reply to myself... I just though this could help other
listers...
It seems that r.le.patch provides a way to get a count of cells by
attribute in each sampling unit with the option att=a5. One must
previously define each attribute value as a group (e.g. with
r.le.setup) and things work fine at least with rectangles. I will have
some control trials with circles later on...
Patrick
Patrick Giraudoux wrote:
Dear listers,
I am exploring r.le and r.li, but I am afraid those two sets of
programmes are providing what I need only partly. Before using them
for shape and diversity analysis, I just would like to get the number
of pixels (or the area) by attributes types (eg the attribute is a
class of CORINE landcover or any classified image) in each sampling
unit into a text file. Sampling units would be circles of a given
radius centered over sites (overlayed on the raste to analyse). I can
provide either a vector file with the center points or imported
polygon shapefiles. Surprisingly it seems that this simple statistics
is not provided in r.le (maybe wrong ?). I suppose this may be due to
the fact there is a much more simple way to do it in GRASS, but
cannot find it in Neteler and Mitasova book.
Any hint welcome,
Patrick
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