Added information on resampling algorithms for overviews #509
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| The overviews (pyramid layers) embedded in the DEA Land Cover COG mosaics were generated using the **MODE** resampling algorithm. This means that, when viewing the data at coarser zoom levels, each overview pixel is assigned the most common land cover class within its corresponding area. |
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@GL-S This text shouldnt be indented. Looks good though.
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| - **MODE** – used for **categorical data**; assigns the most frequent value within the extent of an overview pixel. | ||
| - **BILINEAR** – used for **continuous data** with minimal missing values; interpolates pixels to produce a smooth gradient. | ||
| - **NEAREST** – used for **continuous or categorical data with many missing values**; each overview pixel takes the value of the higher-resolution pixel closest to its centroid. This algorithm appears to maximise the visualisation of products where valid pixels are surrounded by many no-data pixels. |
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@GL-S Could "appears to maximise" be replaced by "optimises" ?
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I'll do some quick testing today, but essentially "nearest" was the only method that wouldn't come out empty if an overview pixel overlapped with a high-res single nodata pixel. So using "nearest" was less about maximising data coverage, but more to ensure our overviews contained at least some data.
I think we can probably go with
- **NEAREST** – used for **continuous or categorical data with many missing values**; each overview pixel takes the value of the higher-resolution pixel closest to its centroid. This algorithm enhances the visualisation of products where valid pixels are surrounded by many no-data pixels.
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Yeah ok, I just wanted to double check this. thanks for confirming!
If you observed it working better to show data, then the statement you suggest is correct. I think it's ok to just describe the effect of applying the algorithm without including too many details on how the algorithm works, considering there is a bit of confusion around it
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I noticed that previously I didn't include any information of the resampling algorithm used. As the mosaics seem to become more popular and considering the new notebook that shows how to access overviews arrays, I think it's important to explain that different DEA products use different algorithms.
I have updated the generic section of the KH and listed the algorithm used in the DEA products offered as mosaics. And I have also added the resampling algorithm in the Land Cover access page, to make that information visible even when people won't click on the general info page.
Please @robbibt, @erialC-P , or @vnewey , double check if I listed the correct algorithm for your products in the general content!
Previews:
general content in user guides --> https://pr-509-preview.khpreview.dea.ga.gov.au/guides/continental-cogs-geotiff-mosaics/
LC access page (under "How to stream DEA Land Cover continental mosaics ...) --> https://pr-509-preview.khpreview.dea.ga.gov.au/data/product/dea-land-cover-landsat/?tab=access