Offline Considerations
Limitations
Browser
OmniSpatial is a Progressive Web Application (PWA), which means that it is an app that's built using web platform technologies, but that provides a user experience like that of a platform-specific app. PWAs offer advantages such as, accessible from any modern web browser, instant offline capability, they're installable, they can be linked via a direct URL, they don't require an app store, and they are always up to date (among other things).
One downside of PWAs over native apps is that, since it is newer/modern technology, certain operating systems and/or browsers do not fully support them, or have limited capabilities.
iOS Limitations
While iOS mostly supports all of the required PWA capabilities of OmniSpatial, there are restrictions when it comes to the amount of storage iOS will allow a PWA to use. The OmniSpatial application uses two types of storage:
- IndexedDB: a standard database available in modern browsers. Omni stores any layer data that is downloaded via a Cache Definition using this storage mechanism
- Cache API: a standard persistent storage API for storing HTTP request/response objects. Omni uses this storage mechanism for storing basemap tiles and any other web content necessary to render the map (such as webmap JSON files, etc.)
iOS’s storage restrictions apply to the combined storage between both IndexedDB and Cache API storage mechanisms. Unfortunately, Apple does not provide a concrete list of rules governing data retention on iOS Safari/WKWebView – so an exact maximum storage value can not be provided.
As such, we recommend caching only the minimum required data for a given task. If you know you are going to an area that doesn’t have coverage, cache that area for offline use and then delete it from the cache when you are done using it.
The amount of allowed storage can potentially be increased by installing the application (adding it to your device's home screen). See Install PWA for more details.