Alpha version of the plugin.

[GiordanoPezzola]

This initial version gives the possibility to download the SRTM 30m DEM of a specified area.

The plugin can be started either clicking the plugin icon from the QGIS toolbar or from the Raster menu --> "QGIS Elevation Plugin" --> "Download Dem for the viewport area".

Note that before launching the plugin it is needed to have an active layer that will be used as a reference for determining the viewport area.

working functionalities:

• Automatic detection of the bounds from the current viewport
• Automatically show the retrieved data on a new layer (if the option is checked)

what's not working:

• the possibility of switching between 30 and 90 meters is still not active. (this will be fixed soon)
• all the errors and messages coming from the elevation script has to be handled in a more precise way

[alexamici]

Looks good, the only minor comment is that probably having the toolbar icon is overkill for a plugin that is not used often. Can you remove it from the PR? If it is long I can accept the PR as is and remove the toolbar later.

[GiordanoPezzola]

You're right. Following your advice I've just removed the plugin's icon from the toolbar, you can check it out from my last commit.