I have different .kmz files, each one contains a .png and a .kml, let's say:
a.kmz, b.kmz, c.kmz.
I would like to use a bash script to obtain a unique .kmz file, let's say d.kmz, that contains all the previous layers.
I simply tried to compress the .kml files and call the result d.kmz, but it does not work.
Bash Scripting KMZ – Merging Different KMZ Layers into a Single File
bashkmlkmz
Related Solutions
If you render raster data into map tiles you have to choose whether you want to create a Google Earth tiles (in Plate Carree) for displaying in KML/KMZ or Google Maps tiles (Mercator) for displaying in the web viewers such as OpenLayers, Google Maps, Leaflet, etc.
These uses two different map projections. Cartographically correct solution is to render two different tile sets with MapTiler (http://www.maptiler.com/) and host these separately.
In the MapTiler in the first screen you can make this choice, either "Mercator tiles" or "Google Earth".
I would recommend to go for two different datasets.
Technically, a hack which would display the Mercator tiles in Google Earth could be done as well - this could run for the deep-zoomed viewes - but if your data covers large regions (countries,states,continents) the differences between the map projections would already be visible as a north-south shift while zooming. See my documentation and source code in python at http://www.maptiler.org/google-maps-coordinates-tile-bounds-projection/ if you are into this approach. Still this is a hack and proper solution is mentioned above - with two distinct tilesets.
From the Google Developers help for Keyhole Markup Language it is clear that Google Earth will only use one KML file from a KMZ no matter how many you put into the folder you zip up to create it:
Include only one .kml file. (When Google Earth opens a KMZ file, it scans the file, looking for the first .kml file in this list. It ignores all subsequent .kml files, if any, in the archive. If the archive contains multiple .kml files, you cannot be sure which one will be found first, so you need to include only one.)
Best Answer
As you know, a KMZ file is a zipped version of a KML file, where the KML is compressed (very helpful for large datasets), and media files such as icon images, overlay images, balloon images, sound files, 3d models and others can be included in the KMZ's zip archive.
When Earth opens a KMZ file, it looks in the KMZ for ONE KML file. Usually there is just one. The convention is to name it doc.kml, but the name isn't important. If it finds more than one, then it will open just one of them. This is likely the issue you're running into by simply combining all the original KML files into one KMZ.
You'll need to actually combine the KML files into one KML, and then zip that up with the PNGs into your KMZ file. This can be done with a variety of software packages, from geospatial processing tools to basic XML tools (since KML is based on XML). If you use an XML tool, you'll probably need to have it open up each KML file, extract the content, and then recombine the contents from each KML into a new KML with the correct KML tags as a wrapper. The "content" you extract can either be the top level container (Document or Folder), in which case you'll need to put them inside a single container in the new file... or you can extract the contents out of that top level container (eg: Placemarks, overlays, etc.), and write those into the new file inside a new top level container.
Alternatively, as mentioned in one of the comments, if you just need to do this once or a few times, you can easily let Google Earth Pro do it for you, by opening your existing KMZ files in Earth, Making a new Folder in your My Places list, dragging the contents of the KMZs into that folder, and then saving the folder out as a new KMZ file.
Good luck.