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I am looking to provide access to a 2 TB Cloud Optimized GeoTIFF (COG).

According to my understanding, it would possible to put this on a S3 bucket, and simply have users access it directly from there.

Alternatively, I could get extra EBS storage (possibly at a significant cost), and have GeoServer serve the COG from an EC2 instance.

My question is: what would be the advantage, if any, of using GeoServer in this situation?

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    A quick glance at the doc would point toward credential managements and mosaiccing
    – JGH
    Commented Jan 4, 2023 at 21:34
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    Even you can create a 2 TB COG that can be used fluently that is not necessarily the best option. A hundred smaller COGs combined together into a mosaic is easier to manage. Geoserver can build the mosaic but there are also other alternatives like STAC. Geoserver can use also STAC as data source.
    – user30184
    Commented Jan 5, 2023 at 0:46
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    The answer depends on what you are trying to achieve. Can you say what the intended use of this data is? Who are the users? What are your security and usage monitoring needs? What kind of processing is needed? How might your users make further use of the data?
    – BradHards
    Commented Jan 5, 2023 at 5:06

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GeoServer serves the images as established standards like WMS and WCS. These can be read by many clients like QGIS, OpenLayers or Leaflet. COGs on the other hand cannot be read by that many clients.

GeoServer can also serve the images in different coordinate reference systems, which is often required. Additionally it can create mosaics of COGs. This means many adjacent COGs would appear as one layer. Additionally COGs can be stores in a time-based mosaic and can then be queried by a timestamp.

Styling is also something that GeoServer can do in contrast to COGs. When you request COGs, you get the raw values of the pixels. GeoServer can provide various styles. This can be useful when you have digital elevation models or continuous data like temperature maps, that you would like display in a classified way.

All in all, GeoServer puts a nicer interface on top of COGs.

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  • What would be the reason you'd want a mosaic of COGs? It was my understanding that a COG already has overviews/pyramids built in. Would you not be recreating that same structure by using multiple COGs? Why not just combine them into one?
    – Andrew Plowright
    Commented Jan 6, 2023 at 23:49
  • Mosaics are not primarily about performance. They stitch together rasters that are located next to each other. this is useful for example if you have many aerial photos of different parts of an area. A mosaic combines them to one layer
    – Jakob Miksch
    Commented Jan 8, 2023 at 11:37
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Jakob has already answered the Geoserver specific part of your question. The more general response, that for example also applies to Mapserver or for that matter something like TiTiler running on API-Gateway/Lambda is that by using Amazon S3 (object Store) vs file system, vs especially block storage (EBS) you can run as much OGC WMS/WMTS or simple tiling (TMS) using just one copy of source COGS in S3. Any number of Geoserver instances can run behind an Elastic Load Balancer, precisely because you can point the Geoserver fleet at the same set of COGs in S3.

Also, when you do things like update one of those COGs in S3, S3 eventing will allow you to update the catalog (STAC, some other raster index etc) meaning any number of applications using those COGs, not just Geoserver, will get updated without additional/unnecessary data movement.

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