Fixed color for specific value

Question

I am trying to make a temperature map, all works fine but I don't know how to have a fixed color palette.

Actually I have this :

rgb.palette <- colorRampPalette(c("blue","green","yellow","orange","red"), 
                                space = "Lab")

image.plot(akima.smooth, 
           col = rgb.palette(NBR.COLORS), 
           main=main_title, 
           horizontal=TRUE,
           axes=TRUE)

This solution works but the colors which are painted are always from blue to red.

For example if the lowest temperature on the map is -10°C the color will be blue, but in another map if the lowest temperature is +25°C that color will be blue too.

How can I define a fixed color panel such as :

-30°C => blue
-20°C => light blue
-10°C => dark green
  0°C => green
 10°C => yellow

If in map 1 lowest temperature is -20 I want "light blue" and in map 2 if lowest temperature is 10°C I want "yellow" color.

Answer 1

If this is fields:::image.plot() then see the arguments to function ?image. In particular the breaks argument is required to set the values for the boundaries of the cut points used to break the input data into the classes for plotting.

The problem you are seeing is that if you don't set breaks then the colour palette is being applied to the range of the input data. If you set breaks then the colour palette is mapped across the full range you want and the data allocated to the groups, and hence the colours, defined by the break points.

I haven't included an example in case this is not fields:::image.plot()