Why does latlon2pix return non-integer values?

Question

Neil Caithness 2011-9-24

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/16635-why-does-latlon2pix-return-non-integer-values

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

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

the cyclist 2011-9-24

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/16635-why-does-latlon2pix-return-non-integer-values#answer_22449

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.

4 个评论
显示 2更早的评论隐藏 2更早的评论

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 2012-2-2