Create a Mosaic Dataset using Cloud Hosted Aotearoa Imagery

In September 2023, Toitū Te Whenua (LINZ) announced that 20TB of their imagery has been made available in a cloud-optimised format using Amazon Web Services (AWS). This is exciting news, as it allows users to add imagery and create mosaic datasets directly from the cloud.

This StoryMap is part of a  collection  explaining how this imagery can be used in ArcGIS including how to access the data from ArcGIS Pro and ArcGIS Enterprise, including how to create image services, mosaic datasets, and basemaps without having to download or locally host the imagery.

This StoryMap will detail how to create Mosaic Datasets in ArcGIS Pro from imagery sourced in the cloud, while covering some best practices when creating mosaics. A mosaic dataset is used to manage, display, analyse, serve, and share raster data.

Later in 2024, elevation data will also be made available through a public S3 bucket.

Firstly, the mosaic datasets need to be stored in a geodatabase. The most common format is a  file geodatabase : this can be created by right-clicking on a folder within the catalog pane and selecting New > File Geodatabase, or by using the Create File Geodatabase tool.

If you want to manage multiple imagery datasets from S3, one option is to create a mosaic dataset for each dataset in the S3 Bucket. These datasets can later be merged into one derived mosaic dataset.

This workflow requires a Standard or Advanced ArcGIS Pro License.

A mosaic dataset item can then be created in the file geodatabase by opening the 'Create Mosaic Dataset' tool, which can be accessed by right-clicking the file geodatabase and selecting New > Mosaic Dataset. The parameters for the tool include:

• Output Location: The file geodatabase for the dataset you've created.
• Mosaic Dataset Name: Whatever you'd like - it may be best to name this after the location and year of the imagery.
• Coordinate System: NZTM, as shown in the second screenshot below.
• Product Definition: Can be set to None.

Once you have created the mosaic dataset, it will appear within the geodatabase you chose in the 'Create Mosaic Dataset' tool.

Next, the ' Add Rasters to Mosaic Dataset ' tool will be used to add the Imagery into the empty dataset.

Select the 'Folder' option under Input Data and select the Browse icon shown by the red arrow below. As we are selecting a cloud-based data source rather than data on your local drive, we can select the Cloud Stores option from the file path directory to access the .acs file for the S3 Bucket (Third Image).  This StoryMap  describes how to create the .acs file.

Regarding the remaining parameters in the second image, minimal change from the pre-defined settings is needed here. Note that the ' Update Cell Size Ranges ' has been left on - this will fill in the Minimum and Maximum Pixel Sizes (minPS and maxPS fields) in the attribute table.

Once the tool has finished running, you'll have a mosaic dataset without having downloaded any imagery to your machine!

You can also add the imagery into a  catalog dataset  alongside other layer types in order to visualise them from a centralised location. However, the catalog layer cannot be used to create tile cache layers.

Once you have created your source mosaic datasets, additional metadata can be added to each source mosaic by adding the appropriate fields to the mosaic dataset's attribute tables. The most important of these attributes will likely be the flight dates (both the Start and End dates). These dates can be accessed from the attribute table of the  NZ Imagery Survey Index  layer from the LINZ Data Service. This information also be accessed using the Command Line Interface from Amazon Web Services: more information on this can be found  here .

By opening the properties of your derived mosaic dataset in the Catalog pane, opening the Defaults tab and navigating to the 'Allowed Mosaic Methods' tab, you can configure the order you'd like your imagery to display on your mosaic. An effective way to do this is by selecting By Attribute as the default method, and use a date field you have created as the Order field. For the purpose of this StoryMap, the Start Date field will be used, meaning newer imagery will now be prioritised in areas where it overlaps with older imagery.

Your requirements for your imagery display order may be more complex - for example you also want to consider whether your urban or rural imagery displays on top in addition to the flight date. In this case, it will be best to create a new field in the mosaic dataset's attribute table with a value that represents the land type.

To learn how basemaps can be created from mosaic datasets, check out  this StoryMap .

For the example in this StoryMap collection, multiple source mosaic datasets from regions in Wellington were created and eventually stitched together to create a derived mosaic dataset for the Greater Wellington region.

If you have multiple source mosaics, you can add them to a derived mosaic dataset. This can be done using the same workflow to how the cloud imagery was added to the source mosaics.

The image below provides an example of parameters for the 'Add Rasters to Mosaic Dataset' tool when creating Derived Mosaics.