3D Graph to analyze the value of texture maps Introduced in Chapter 1.4
Let me give you a quick breakdown of how the file works:
If you go into solid view, you can see that the scene consists of a whole bunch of intersecting planes.
Those have a shader that samples the texture's value from the XY-coordinates and mixes between transparency and emission by comparing the Z-coordinate to the value of the texture.
So a single one of these planes shows a simple line of the profile at the plane's position.
All together they create the whole graph by using a grid of planes.