[GRASS-dev] How obtaining the area of a cell

GRASS GRASS developer
1

Hello everyone,
I would like to know if there’s a GRASS function that returns the cells area in a raster map.

Regards,
Roberto

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2

Yes, there is. You forgot to say where You need it - in C code, script?

G_area_of_cell_at_row(row); [1]

Maris.
1. http://download.osgeo.org/grass/grass6_progman/gis_2area_8c.html#0f6fbb86c2dc8fa911eb52dc4875aab3

2008/4/10, roberto caselli <roberto.caselli@yahoo.it>:

Hello everyone,
I would like to know if there's a GRASS function that returns the cells area
in a raster map.

Regards,
Roberto

________________________________
Inviato da Yahoo! Mail.
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3

Thank you Maris, I’m working on a C++ module.

Maris Nartiss maris.gis@gmail.com ha scritto:

Yes, there is. You forgot to say where You need it - in C code, script?

G_area_of_cell_at_row(row); [1]

Maris.

  1. http://download.osgeo.org/grass/grass6_progman/gis_2area_8c.html#0f6fbb86c2dc8fa911eb52dc4875aab3

2008/4/10, roberto caselli

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4

Sorry for this silly question but I have a doubt now: Can an elevation raster map have cells with different areas? I though that all cells in a map had the same sizes…

Maris Nartiss maris.gis@gmail.com ha scritto:

Yes, there is. You forgot to say where You need it - in C code, script?

G_area_of_cell_at_row(row); [1]

Maris.

  1. http://download.osgeo.org/grass/grass6_progman/gis_2area_8c.html#0f6fbb86c2dc8fa911eb52dc4875aab3

2008/4/10, roberto caselli

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5

roberto caselli wrote:

Sorry for this silly question but I have a doubt now: Can an elevation
raster map have cells with different areas? I though that all cells in
a map had the same sizes...

All cells have the same dimensions measured in the location's
coordinate system.

However, for lat/lon data, each cell will have fixed dimensions in
degrees, but it's physical area will vary with latitude.

This is why G_area_of_cell_at_row() takes the row as an argument.

For projected data, it returns a constant value based upon the
region's resolution and the location's units (metres, feet, etc). For
lat-lon data, the conversion takes into account the row's latitude and
the location's ellipsoid.

Also, note that G_begin_cell_area_calculations() must be called to
initialise the conversion parameters prior to calling
G_area_of_cell_at_row().

--
Glynn Clements <glynn@gclements.plus.com>