Images below are rendered from a synthetic test data set and are for demonstration purposes only.
The color scale used for %RE (percent relative emission) in the 3D plume render. All four options are perceptually-ordered scientific colormaps (not a rainbow scale) — low response reads as a cool/dark color, high response as a bright warm one.
Users have the option of including a transparency threshold. Any interpolated %RE value at or below this threshold renders fully transparent. Use this option to reduce background noise in the image. For example, see the histogram of values from the synthetic test dataset below. Adjusting the transparency threshold (in this case, to 5%) hides values on the low end of the distribution, making the higher-response areas easier to see in the 3D image.
Once the threshold above has defined a visible range, we use a gamma function to control how transparency changes across that range — from fully transparent at the threshold to fully opaque (solid) at the dataset's peak value. The "Gamma value" field defines the ramp's steepness.
Transparency is decreased to the power of the value. Positive values (e.g. 2, 3) suppress everything but the strongest response, for a sharper, more solid hotspot with a thinner halo. Negative values (e.g. -2, -3) do the opposite, boosting visibility of faint, near-threshold response — useful if you want weak trace response to stay visible instead of fading into the background. A value of 1 or -1 is a linear ramp, where transparency decreases in direct proportion to %RE (this is the default).
The 2D and 3D views each have their own, independent Gamma value — moving the slider on one tab does not change the other, and switching tabs re-shows whichever value that tab is currently set to. This is deliberate: the same gamma number produces two genuinely different-looking results in the two views.
This is because the 3D viewer draws the plume as many small, partially transparent glyphs, and the gamma value on the slider affects each individual glyph. From most viewing angles, you are actually looking at many glyphs "stacked" on top of each other. The result is that many individual glyphs are blended together to form a color and transparency that appears much more opaque than any individual glyph. The 2D plan view has no such stacking effect — it shows the single strongest %RE value found at each location, colored by that one value alone (see the interpolation methodology page for why it's the max, not an average). So at the same gamma value, the 2D view shows a single object while the 3D view shows dozens of partially-transparent copies stacked on top of each other. This is why the 3D view appears far more solid for what is, numerically, the same setting.
To compensate, the 2D view starts at a much more aggressive default gamma (-5, boosting faint response heavily) than the 3D view typically uses, so a freshly-opened 2D view reads closer to what the 3D view already shows. This is a reasonable starting point, not an exact match — a single gamma curve mathematically can't reproduce the shape of ~70 stacked, blended glyphs (notice in the chart above that even the boosted 2D curve still falls short of the 3D curve especially near the threshold) — so feel free to keep adjusting the 2D tab's own Gamma slider from there until it looks right for a given site.
The 3D plume in the interactive viewer is drawn as a cloud of many individually-colored glyphs (small shaded spheres, one per interpolated location), not a solid surface. Each glyph is sized in on-screen pixels, not real-world units — so the same glyph size can look perfectly smooth at one zoom level or boring layout and show visible gaps at another, since a fixed pixel size covers fewer real-world inches the closer you zoom in. The app automatically picks a sensible starting size for your specific data, but if you ever zoom in and start seeing a gapped or checkerboard-like pattern, drag this slider up until it smooths back out — or drag it down if a hotspot looks overly soft or bloated for your liking.
This only changes how the existing data is drawn, and only in the 3D viewer — every interpolated location stays part of the same underlying data, with the same %RE value, no matter where this slider sits.