This article follows a previous tutorial that described how to use the “Finder tool” in the Explorer mode of the HEritage Data VIsualisation tool (HEDAVI). We now focus on the next step to make your own HEDAVI stories: creating and organising selected data in the Explorer layer stack.

The layer stack is a powerful tool that organises multiple layers in the same manner as a Geographic Information System (GIS). You can add multiple vector and raster layers, organise them in a tree structure, expand and collapse folders, show or hide a folder or a layer, and change the Base map or the Elevation Model (in 3D visualisation).

It is also possible to import all or a part of a previous layer stack, the save, export / import and share mechanisms, and these functions will be described in a future tutorial.
 

1 Opening the layer stack 

You can open the layer stack using the 3-layers button on the right of the screen.

2 Adding layers 
 

2.1 Base maps

The “Base map” is a global map that remains at the bottom of the layer stack. Other layers are added on top of the base map. The MERIS Mosaic is the default base map. 
 

2.1.1 Change the Base map

To change the Base map, open the “Services Panel”. The “Base maps” tab opens by default.

Select the Base map you would like to use from the available list and the base map will be changed. Some Base maps have several versions, which can be accessed by right clicking on the base map option in the menu (e.g. the Sentinel-2 Cloudless map) as shown in a previous publication.
 

2.1.2 Add a Base map as an overlay

You can also add a Base map as an extra global layer on top of the previous Base map by right clicking the Base map you want to add to the layer stack, and then selecting “Add as an overlay”.

2.1.3 Add a vector overlay

It is possible to add toponymy or world borders in the layer stack. Use the “Overlay Maps” button located under “Background Maps” in the “Base maps” tab then select the overlay you would like to use.  

 You can change the colour of “World Borders” by right clicking the option in the Overlay Maps section and then selecting the colour you prefer. The following image demonstrates how to change the colour from the default black to yellow instead.

2.1.4 Change the 3D Elevation Model

To change the 3D elevation model, open the Elevations tab in the “Service Panel”.

The Copernicus Global DEM-30 model is the default, but you can select any other option in the list to change to another model. After you select a model, the layer stack is updated and you can check this by activating 3D visualisation and examining a tiled, close-up view of mountainous areas.

2.2 Add a vector layer

Vector layers can be added from the “Finder” tab of the Service Panel.

On this tab, tick the “Area of Interest” checkbox, then draw / upload / select a vector using the “Area of Interest” tool in the same way you would search for data.

2.2.1 Drawing a vector

Draw geometric shapes using the dedicated tool on the “Display area” ( first button from the left). Icons will appear in the “Geometry builder” at the top right of the image area to define a bounding box (default selection), a circle, a polygon or a corridor.
 

2.2.2 Uploading an external vector

Vectors can also be added in the layer stack by importing a closed single polygon without holes contained in a KML, KMZ or SHP file (second button from the left).
 

2.2.3 Creating a vector from an item in the layer stack

Geometric shapes can also be defined by using the footprint of another layer in the layer stack ( third button from the left), the camera is centred on the currently selected item.
 

2.3    Adding a raster layer

You can add raster layers to the layer stack from search results through the “Finder” tool. The search will show a list of products that match the selected criteria. Selecting any of these results will add the layer to the “Temporary display” panel. If you select another product, it will replace the one added to the Temporary display panel.

To add multiple products as new layers, use the CTRL (discontinuous selection of all clicked products) or the Shift (continuous selection of result range between first and last click) keys.

2.3.1 Adding a raster product

To add the selected product(s) to the layer stack itself instead of the Temporary display, either double-click your selection or right click on it and then use “add to layer stack” in the menu.

2.3.2 Product status

The rendering of a raster product in the layer stack depends on its status. If it is “Ready”, it can be displayed up to full resolution; otherwise, it first needs to be prepared to be displayed. To do so, right-click on the name of the product and select “Prepare data”.

•  “Ready” means the product has already been downloaded and prepared, it can be visualised and analysed immediately
•  “In progress” means the selected product is currently under preparation, its percentage of completion is displayed

•  “In queue” means that the product has been sent to the preparation queue but is not yet being prepared
   
•  “Unprocessed" means that the product has not been requested and must be prepared before it can be displayed. This is the default status.
•  "Corrupted" means the product has been prepared but flagged as corrupted by an administrator
   
• “Error” means the product is not available since something unexpected happened in a previous preparation, causing an error.

3 Organising layers

All the layers in the stack can be organised in a tree structure with folders and subfolders.

3.1 Creating a folder

To create a folder, right-click in the layer stack and select “Create folder” in the menu. Alternatively, if you select “Add to new folder”, you will similarly create a new folder but the folder / product on which you right-clicked will also be added to this folder.
You can then specify a name and a description for your new folder. Use the “Validate” button to create the folder.
 

3.2 Renaming a layer

Any product or folder can be renamed by right clicking on the layer and selecting “Edit label and description” in the menu.

3.3 Collapsing / expanding a folder

Any folder in the stack can be collapsed (hiding the name of the layers/sublayers it contains) or expanded (which reveals its content) by clicking on the arrow on the left of the name of the layer.

3.4 Showing / hiding a layer

Any layer can be ticked (showing its content in the display area) or unticked (which removes its content from the display area) by clicking on the checkbox next to the name of the layer.

3.5 Moving layers

You can move any item in the layer stack tree structure by selecting a node and dragging and dropping the item to another position in the stack. This will also move any sublayers under the item you move.

To adjust the order of any items in the layer stack and within folders, you will need to use horizontal or vertical positions to place the item at the intended level. This will determine whether the item is shown at the bottom of a folder, or outside and after the folder in the layer stack.

3.6 Deleting items

3.6.1 Deleting a layer

You can delete a layer, (either a product or a folder) and its content by right clicking on its name in the layer stack and then using the “Delete from layer stack” option. You will be prompted to confirm you wish to proceed before the layer is deleted.

3.6.2 Deleting the contents of a folder

It is also possible to delete the contents of a folder while keeping the folder itself. To do so, right-click the chosen folder, then use “Delete content” and confirm you wish to proceed when prompted.

Conclusion

The use of layer stacks will help you to organise any data products you want to work with in HEDAVI, and you can easily adjust the layer stack using the available options.

The next tutorial will show you different ways to process products in a layer stack, in order to improve the visual rendering or highlight information in your images.