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Contouring color ramp: no color or transparent color fill?

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I set up a new color ramp for contouring.

I want to show drawdown values: blue for positive values, red for negative values and white to zero value.

Is it possible to assign no color to the zero values so that I can see the raster map under the contouring layer?

My workaround was to save GMS project to image file, open it in Quantum GIS and set the transparent color to white.

Thank you

Daniele

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Daniele,

On our wiki page, GMS: Contour Options, it gives the option for using a log interval. "If the Log interval option is selected, all contour intervals will be positive. No contours are drawn in areas where the data values are zero or negative. Furthermore, a 'Starting value' must be entered. This value represents the minimum contour value." Thus, you have the option of assigning no contours to zero values, but it also affects your negative value contours, as well. So, I don't think this option will help you in this particular project.

Another option is to manually edit and define the contour ramp. Using this option will not allow you to assign no color to zero values, but it will accommodate your other needs. To do this, click on Display then Display Options... in the top ribbon of GMS. Click on "Options" next to Contours. Under "Contour Method," select "Color Fill" and "Use Color Ramp." Specify your range (if needed). Click on "Color Ramp... ." Next, click "User defined" under "Palette Method," and "Edit Table..." to assign colors to the appropriate place. Please note: although the option for negative values may not appear when you click on edit table, the ramp is used to assign a color to a minimum value, a middle value, and a maximum value, and an appropriate contour ramp should display itself after clicking "OK."

What I recommend is using the latter option and setting transparency to some value (maybe 50%?) that will allow you to have the ramp you desire with some of the effect of looking through the zero or white colored contours; or, use the workaround you mentioned in your initial query!

Let us know if you have any further questions!

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Old post here, but I was looking for a similar functionality for SMS and stumbled on a work-around for setting a specific range of values to transparent (maybe it'll work for GMS?)

I used the dataset toolbox, modification tool (filter) to set values near zero to 'null'.  Then the color ramp can still be solid, but the 'null' values will be transparent.

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