RE: ColorData as a Funnction of height values

*To*: mathgroup at smc.vnet.net*Subject*: [mg93240] RE: [mg93220] ColorData as a Funnction of height values*From*: "David Park" <djmpark at comcast.net>*Date*: Sat, 1 Nov 2008 05:05:42 -0500 (EST)*References*: <18277846.1225441934632.JavaMail.root@m02>

Here is a sample set of data. I am going to uses a case that is general enough so that you should be able to use it as a model for your own data. data = Flatten[ Table[{x, y, Sin[x^2 + y^2]}, {x, -2, 2, 0.1}, {y, -2, 2, 0.1}], 1]; First, I will use the SouthwestColors scheme, which I clicked in from the ColorSchemes palette. It goes from a dark red to blue, and you want the opposite. So I made the ColorFunction a pure function and used 1 - zvalue instead of zvalue. That reverses the color direction. Next I set ColorFunctionScaling to False so that we will work with the actual z values of your data. Often, it is easier to work with the actual data values. You could obtain these values by making a preliminary ListContourPlot and looking at the contour values, or by using NMaximize and NMinimize. Then I used the Rescale expression to rescale the minimum and maximum z values, {-1,1} in this case, to go from 0 to 1, which are the color gradient coordinate. So then we can make the main plot. mainplot = ListDensityPlot[data, Mesh -> None, InterpolationOrder -> 2, ColorFunctionScaling -> False, ColorFunction -> (ColorData["SouthwestColors"][ 1 - Rescale[#, {-1, 1}]] &), ImageSize -> 400] Next we make a legend. (Don't use the regular Mathematica Legend command. It's pretty awful.) We make our own much nicer legend, by making a ContourPlot where Z goes from out minimum to maximum values and we pick an appropriate set of contours. We use the same ColorFunction and Scaling as in the main plot. We make the ticks the same as the contours and put them on whichever side we want. legendplot = ContourPlot[z, {x, 0, .2}, {z, -1, 1}, AspectRatio -> Automatic, Contours -> Range[-1., 1., .25], ColorFunctionScaling -> False, ColorFunction -> (ColorData["SouthwestColors"][ 1 - Rescale[#, {-1, 1}]] &), PlotRangePadding -> 0, FrameTicks -> {{None, Range[-1., 1., .25]}, {None, None}}, ImageSize -> {Automatic, 300}] Now, we just combine the two plots in a Row. Row[{mainplot, Spacer[20], legendplot}] David Park djmpark at comcast.net http://home.comcast.net/~djmpark From: olalla [mailto:operez009 at ikasle.ehu.es] Dear all, I have a long list of numerical values, {x,y,f(x,y)}, representing the value of a field in the points (x,y). I want to visualize them using ListContourPlot or ListDensityPlot. I have two poblems: 1. I want to change the colour to a usual scale of Blue-Minimum and Red-Maximum, or to make something similar to ColorFunction -> Function[{x, y, z}, Hue[z]] but with my numerical data, not with a function. How can I do this? 2. When including a legend with ListContourPlot or LisDensityPlot, how can I include the white colour which is already included in the plot but not in the legend? Thanks in advance Olalla P=E9rez UPV/EHU=