Why does latlon2pix return non-integer values?

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Neil Caithness
Neil Caithness 2011-9-24
latlon2pix converts latitude-longitude coordinates to pixel coordinates.
[row, col] = latlon2pix(R,lat,lon)
So, as I understand it the output should be integer row and column indices into the map defined by R so that map(row,col) returns the pixel in map that contains the point [lat,lon].
I have ...
R =
0 -0.0028
0.0028 0
23.6282 -22.0506
lat = -23.8750
lon = 27.6250
then
[row, col] = latlon2pix(R,lat,lon)
returns
row = 657.1850
col = 1.4396e+003
so I have to resort to floor(row) and floor(col) before using them as subscripts. I suspect this may not be returning the intended pixel.
Any suggestions appreciated.
Best Wishes
Neil

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the cyclist
the cyclist 2011-9-24
I don't have the Mapping Toolbox. But reading the documentation for the latlon2pix() function, I see no indication that the output is necessarily integer pixel values. In fact, the example here: http://www.mathworks.com/help/toolbox/map/ref/latlon2pix.html explicitly mentions getting a column value of 0.5.
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Walter Roberson
Walter Roberson 2011-9-24
Exact pixels would make sense for people who want to be able to create sub-sampled graphics. It is easy to throw away precision that you do not need, but difficult to regain precision that was thrown away on your behalf.
Neil Caithness
Neil Caithness 2012-2-2
Thanks. Getting the higher precision return is of course preferable.
ROUND (rather than FLOOR, as I expected) returns the correct absolute pixel values.

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