I want to apply two different emission intensities depending on
the position of the camera or an object
The transition between the different intensities should be smooth but irregular(Random)
(like using DELETE modifier + Soft selection)
I tried it using a switch but it does not work
[attachment=0]magma.jpg[/attachment]
The Switch expects as Boolean value (true or false). So you need to specify a condition (e.g. Greater than a threshold) for it not to error out.
I also added a Noise to the Threshold based on the particle position, so you get some jittering at the border. Without the Add, you get a straight line.
The Power op kills your sign, so without it you can have the Threshold be > 0 and < 0 to move the border. With it, you can move only one way…