Using negative values in an intensity plot

[Joe_McC]

I want to plot a 2D array in an intensity plot. The data are a series of spectra from a spectrum analyser so the array elements have negative values (can range from -90dBm to +10dBm) I want to plot it using a color table? I've only done this before using positive data in the array. I can't map colors to the negative data.

Thanks for any pointers,

Joe

[0utlaw]

Hi Joe,

Are you using an LabVIEW Intensity Chart/Graph or another type of indicator?  These are both certainly compatable with negative values, you should just be able to change the scale to match your ranges.  If anything, you might need to ensure that your representation is set to something that supports negative values.

If you need to for some reason, you could also just offset the values - add 90 dBm to everything to make the values positive.

Regards,

[johnsold]

Joe,

Just type the values onto the ramp.  The default is 0 to 100, but it let me type +10 and -90.

Did you somehow convert the indicator to an unsigned data type?

Lynn

[Joe_McC]

If I use the standard intensity graph without a color table (default black-blue-white scheme), I can see the plot, but the scale beside it shows all black with the min & max values labeled (-88 to -35 dBm). At a minimum I'd like to have this scale reflect the colors in the plot. Ideally I'd like to use a color table to define the colors used. I'd rather not make the values positive a that is messy....

Thanks,

Joe

[Joe_McC]

Lynn,

At least your plot scale is correct. I'll try to re-examine mine. The intensity graph I have is a floating point representation.

Thanks,

Joe

[0utlaw]

Hi Joe,

The option to auto-scale the intensity map can be turned on/off by selecting the "Autoscale Z" option in the scale's right-click menu.  You may also need to play with the color spectrum to modify the mapping.

Regards,

[johnsold]

Color Table Property Node for the graph.

Lynn

[Joe_McC]

Guys, that works now. Now I have to investigate exactly why! I deleted all & atarted again & now all is well.

Thakns for the help.

Joe