Cloud Optimized GeoTIFF

A Cloud Optimized GeoTIFF (COG) is a standard GeoTIFF file whose internal layout is reorganized to allow clients to fetch only the required portions of the file over the internet. It achieves this through internal tiling and embedded overviews, combined with HTTP range requests, enabling efficient streaming and visualization of large raster datasets in cloud environments.

A Cloud Optimized GeoTIFF (COG) datasource must provide the raster data in crs EPSG:3857. If the COG is in a different CRS, it must be reprojected to EPSG:3857 before being added as a datasource. Furtermore tiling must be aligned to the TMS scheme. If the COG does not meet these requirements, it cannot be added as a datasource and will result in an error. We also strongly recommend to use for compression the LZW method, as this allows for better performance when accessing the data and avoids errors due to unknown compression methods, like zstd, which are not supported by all geotiff libraries.

The following table provides an overview of the options:

Option	Description
Name	Name of the Datasource.
Description	Description of the Datasource (optional).
Bounding Box	Describes the bounding box of the data. Clicking the button "Edit Bounding Box" opens a new map window where a bounding box can be defined interactively. Clicking the button "Draw new extent on map" activates the bounding box mode, allowing the user to define a bounding box by clicking twice on the map (e.g., top-right and bottom-left corners of the bounding box). The coordinates of the bounding box are automatically adopted in EPSG 4326. Clicking the button "CLOSE" closes the map window.
URI	URI of the datasource.

Option

Description

Name

Name of the Datasource.

Description

Description of the Datasource (optional).

Bounding Box

Describes the bounding box of the data.
Clicking the button "Edit Bounding Box" opens a new map window where a bounding box can be defined interactively. Clicking the button "Draw new extent on map" activates the bounding box mode, allowing the user to define a bounding box by clicking twice on the map (e.g., top-right and bottom-left corners of the bounding box). The coordinates of the bounding box are automatically adopted in EPSG 4326.
Clicking the button "CLOSE" closes the map window.

URI

URI of the datasource.

Minumum level

The minimum zoom level for which tiles are available in the COG. This should be set to the lowest zoom level for which the COG contains data. Setting this value correctly allows the system to avoid requesting tiles at zoom levels where no data is available, improving performance and reducing unnecessary requests.

Maximum level

The maximum zoom level for which tiles are available in the COG. This should be set to the highest zoom level for which the COG contains data. Setting this value correctly allows the system to avoid requesting tiles at zoom levels where no data is available, improving performance and reducing unnecessary requests.

Tiling scheme

The tiling scheme used in the COG. This should be set to "Mercator" if the COG is tiled according to the TMS scheme and uses EPSG:3857, which is commonly used for web mapping applications. If the COG uses a different tiling scheme like "Geographic" (EPSG:4326), it should be set accordingly. Setting this value correctly ensures that the system can correctly calculate tile coordinates and request the appropriate tiles from the COG.

Convert to RGB

If the COG contains data in a format that is not directly supported for visualization (e.g., single-band or multi-band data with non-RGB bands), enabling this option will convert the data to RGB format for display purposes. This can be useful for visualizing certain types of raster data, but may result in increased processing time and memory usage, so it should be used only when necessary.

Normalize

If the COG contains data with a wide range of values, enabling normalization can help improve visualization by scaling the pixel values to a more manageable range. This can enhance contrast and make features more visible, but may also result in loss of detail in areas with subtle variations, so it should be used with caution.

Interpolate

If enabled, this option will apply interpolation when rendering the COG at zoom levels where the native resolution of the data does not match the display resolution. This can help improve visual quality by smoothing out pixelated edges, but may also introduce blurring or artifacts, so it should be used based on the specific requirements of the visualization.

After all settings have been configured, the data source must be saved. It can then be viewed as a 2D map or as an overlay on a terrain layer in the preview (button 'Activate Map').

Data Preview

The data preview allows a visual check of the configured data source before publication. It displays the data in the map window using the selected projection and within the defined extent. Users can interactively pan and zoom the map to review the display.
Changes to the data source or the extent are applied to the preview after clicking “Reload Map.”