9-4. Other composite styles¶
Optional: create an exclusivity set¶
We are going to be copying the Bristol Sentinel 2 layer a few times now as we work with different visualisations. We can create a set of layers as "mutually exclusive", so that switching one on turns the other one off. This is not essential, but useful for this and future exercises.
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On the layers tab of the UI, scroll to the bottom beneath all your layers and base layers until you get to Exclusivity sets. Type bristol-s2 into the text entry box then select + Add.
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On the top row of the Bristol Sentinel 2 layer card, select the pencil icon on the right to Edit the layer definition. Scroll to the very bottom and tick the check box next to the bristol-s2 set you just added.
Duplicate the layer and create a new visualisation method¶
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On the top row of the Bristol Sentinel 2 layer card, select the duplicate layer icon - two overlapping blue squares, with a tooltip.
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On the Bristol Sentinel 2 (copy) layer, click the red trash can icon next to the RGB visualisations to clear the current settings, then click the pencil icon to set a new visualisation. Choose one of interest - the Composite options table below explains each one.
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Now edit the layer names - change Bristol Sentinel 2 to Bristol Sentinel 2 natural colour and Bristol Sentinel 2 (copy) to something meaningful.
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Open the Preview. Admire your work.
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Tweak your visualisation stretches. If you want, repeat the last few steps for different visualisation options.
Composite options¶
Each option asks a different question of the same scene. The bands are picked for you from the bands your dataset actually has.
| Option | Bands used | What to look for around Bristol |
|---|---|---|
| Natural colour | Red, Green, Blue | The scene as your eye would see it — the baseline for comparing everything else. |
| False colour infrared | NIR, Red, Green | Healthy vegetation shows bright red, so Leigh Woods and the farmland to the south-east stand out against grey urban areas. |
| Agriculture | SWIR1, NIR, Blue | Separates crops, bare soil and water — fields east of the city take on different hues depending on what is growing. |
| Urban / geology | SWIR2, SWIR1, Red | Built-up areas come to the fore: the city centre, Avonmouth docks and the industrial estates along the river. |
| Custom | Any three you pick | Build a combination of your own — swap the blue band for a shortwave infrared band and see what changes. |
Different data, different bands
The exact bands behind each option depend on the file you are looking at. A 10-band Sentinel-2 stack and a 3-band RGB image cannot offer the same views, so an option may be missing or resolve to different bands elsewhere.