Now we just create a visualization of the GTC dataset, which is to render the scalar field on one cross section over time via volume rendering. One rendering image is shown in the left top. Here the group ID is 31, the scalar field is the electrostatic potential (phi). The color is linearly mapped from the scalar to a color space, where a portion near zero is transparent. In this image, the time axis is aligned with the horizontal axis in the image, where the left(right) side means the earliest(latest) of the simualtion.
This image can be compared with its histogram of the scalar field over time, which is shown in the left bottom. Similar to the left top image, the horizontal axis represents the time, where the left(right) side means the earliest(latest) of the simualtion. Each column in this image then represents the histogram at one time step. The histograms are aligned so the entry including scalar zero is vertically aligned to red horozontal line in the image, and each histogram is draw as a vertical white bar, whose vertical length is protional to the scalar range of the corresponding time step. The time histogram clearly shows that after the first half of the simulation, the range of scalar field becomes stable in a limited range. Consequently, when assigning color/opacity to the scalar field, we can mainly consider the scalar field near the end of the simulation.
