diff --git a/docs/data/product/dea-land-cover-landsat/_access.md b/docs/data/product/dea-land-cover-landsat/_access.md index 51ab8f653..94ba5a18a 100644 --- a/docs/data/product/dea-land-cover-landsat/_access.md +++ b/docs/data/product/dea-land-cover-landsat/_access.md @@ -33,6 +33,13 @@ For detailed instructions, please visit the [Continental Cloud-Optimised GeoTIFF
The animation above shows the DEA Land Cover COG mosaic moving from the continental-scale down to the 30m x 30m pixel level.
+:::{admonition} Note +:class: note + +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. + +::: + :::{dropdown} How to integrate DEA Land Cover continental mosaics into your own Python workflow You can seamlessly open a Land Cover mosaic, such as Level 4 for year 2024, using Python and the `rioxarray` library. For example: diff --git a/docs/guides/continental-cogs-geotiff-mosaics.rst b/docs/guides/continental-cogs-geotiff-mosaics.rst index 3076bd20e..59bcc1205 100644 --- a/docs/guides/continental-cogs-geotiff-mosaics.rst +++ b/docs/guides/continental-cogs-geotiff-mosaics.rst @@ -7,11 +7,17 @@ Some Digital Earth Australia (DEA) products are provided as **continental-scale These datasets are made available as **Cloud-Optimised GeoTIFFs (COGs)**, a format that enables users to efficiently *stream* raster data directly from the cloud without downloading the files. This provides a fast and convenient way to access full-continental coverage from tools like QGIS or ArcGIS Pro, especially when working with large datasets. +COGs include overviews, which are lower-resolution pyramid layers that allow fast rendering at different zoom levels. When zooming out, GIS software displays a coarser overview to improve performance. These layers are generated using a **resampling algorithm**, which determines how pixel values are aggregated when reducing spatial resolution. For DEA products, the choice of resampling algorithm depends on the nature of the data: + +- **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. + Not all DEA products provide continental-scale COGs. Currently, this access method is only available for selected products: -- `DEA Land Cover `_ -- `DEA Intertidal `_ -- `DEA Tidal Composites `_ +- `DEA Land Cover `_ - uses `MODE` as the overview resampling algorithm +- `DEA Intertidal `_ - uses `NEAREST` as the overview resampling algorithm +- `DEA Tidal Composites `_ - uses `NEAREST` as the overview resampling algorithm **VRT (Virtual Raster) files** are provided alongside the ``.tif`` mosaics. These files serve as lightweight wrappers around the main data and can be used to open data in GIS software with visual settings already applied. We use VRTs to provide: