Several of the global DEMs listed in the post on Digital Elevation Models (DEMs) come as tiled layers in geographic (latitude and longitude) postions. Some also require that you have an account and give your credentials before accessing. Once you have accessed and downloaded the tiles, it makes no sense importing individual tiles to Karttur´s GeoImagine Framework. Instead you should create a virtual mosaic of the raw tiled data, import (organize) the mosaic and then tile the mosaic into the Framework projection system.
Overview
This post will take you through the steps for searching, downloading, exploding, mosaicking and importing Copernicus DEM data. The first parts deals with the 90 m version available from https://gisco-services.ec.europa.eu/dem/copernicus/outD/. These tiles come as zip files and requires exploding before mosaicking. The versions available from AWS do not require any prior search or unzipping but are retrieved as geotiff files and if you just want to process them, you can skip to the section called Mosaic ancillary.
Search tiles
Many global datasets are delivered as tiles and to access them using machine scripting you must list the urls beforehand. For the Copernicus DEM data available from https://gisco-services.ec.europa.eu/dem/copernicus/outD/, the process SearchCopernicusProduct searches and lists all the Copernicus 90 tiles.
The search results in a html file that lists all the available urls. The Framework process DownloadCopernicus loops the html file and downloads all the listed tiles.
To actually import the tiles, we are first going to create one large, global and virtual mosaic, and then import just this virtual mosaic. In later steps you will tile the DEM into the default systems used by the Framework, but starting with the virtual mosaic.
The Framework contains a special process, MosaicAncillary, for creating a list of all files of a particular kind or pattern. Setting the parameter mosaiccode to subdirfiles the process recursively traverses all subfolders under a root.
Import the virtual mosaic as an ancillary layer to the Framework with the process OrganizeAncillary. Before you do that you need to check in the original virtual mosaic that the link to the original tiles is absolute - alternatively you need to create the original mosaic in the destination folder of the import function.
Before you can tile the mosaicked original DEM data you must have created a project and a region for your user that defines the tiles to create. How to do that is covered in the post on Arctic DEM. In the example below I have a projectid and tractid called karttur-northlandease2n that is based on a default region called northlandease2n. This region is defined using EASE-grid North (EPSG:6931) and covers all tiles that contain at least a single cell of land. The Framework for this region is ease2n. In essence this means that the global Copernicus DEM mosaic will be tiled into 104 seamless pieces that together cover all land masses of the northern hemisphere above approximately 30 degrees North.
