Map Download by Specifying a Bounding Box or Route
Map data can be fetched into a persistent cache (with default size of 256 MB) to enable offline map capabilities by specifying a bounding box or radius around a route. This can be done through the NMAMapDataPrefetcher
and associated classes. The NMAMapDataPrefetcher
provides a set of methods to estimate the size of fetches (in KB), initiate fetches, cancel fetches, and clear the map data cache.
NMAMapDataPrefetcher and NMAMapDataPrefetcherListener
NMAMapDataPrefetcher
is a singleton which must be obtained using the sharedMapDataPrefetcher
method. The next code examples shows basic NMAMapDataPrefetcher
use.
estimateMapDataSizeForBoundingBox:error:
or estimateMapDataSizeForRoute:radius:error:
methods: NMAPrefetchRequestError error = NMAPrefetchRequestErrorNone;
NSInteger requestId =
[[NMAMapDataPrefetcher sharedMapDataPrefetcher]
estimateMapDataSizeForBoundingBox:bbox error:&error];
To start NMAMapDataPrefetcher
fetch, use fetchMapDataForBoundingBox:error:
or fetchMapDataForRoute:radius:error:
.
NMAGeoBoundingBox* bbox = …
NMAPrefetchRequestError error = NMAPrefetchRequestErrorNone;
NSInteger requestId = [[NMAMapDataPrefetcher sharedMapDataPrefetcher] fetchMapDataForBoundingBox:bbox error:&error];
...
To cancel NMAMapDataPrefetcher
fetch, call the cancel:
method.
NSInteger requestId = ...
[[NMAMapDataPrefetcher sharedMapDataPrefetcher] cancel:requestId];
...
NMAMapDataPrefetcher
operations are performed asynchronously. When available, the results of these operations are passed on to NMAMapDataPrefetcher
’s listeners. Listeners must implement the NMAMapDataPrefetcherListener
protocol. The callbacks of the NMAMapDataPrefetcherListener
protocol are:
prefetcher:didUpdateProgress:forRequestId:
- Called during map data fetches to indicate the progress completed in the range of [0…1] for a request ID.prefetcher:didUpdateStatus:forRequestId:
- Called during map data fetches to indicate status for a request ID.prefetcher:didPurgeCache:
- Callback to indicate that the cache has been cleared of any unused map data.
NMAPrefetchStatus Enum
NMAPrefetchStatus
is an enum data type that represents the status of NMAMapDataPrefetcher
fetch operations. This status is returned through the NMAMapDataPrefetcherListener
protocol.
NMAPrefetchStatusInProgress
-NMAMapDataPrefetcher
fetch operation is still in progressNMAPrefetchStatusSuccess
-NMAMapDataPrefetcher
fetch completed successfullyNMAPrefetchStatusFailure
-NMAMapDataPrefetcher
fetch operation had failed to completeNMAPrefetchStatusCancelled
-NMAMapDataPrefetcher
fetch operation was cancelled
The NMAPrefetchRequestError Enum
NMAPrefetchRequestError
is an enum data type, representing any errors encountered when initiating a NMAMapDataPrefetcher
fetch operation.
NMAPrefetchRequestErrorNone
– No errors dispatching the request.NMAPrefetchRequestErrorUnkown
– An unknown error has occurred during request submission.NMAPrefetchRequestErrorBusy
– The number of requests is at max capacity.NMAPrefetchRequestErrorInvalidParameters
– The request was invalid due to invalid parameters.NMAPrefetchRequestErrorOperationNotAllowed
– ODML prefetching permission is missing.
Check the network connectivity at the application level to ensure NMAMapDataPrefetcher
operations are only performed when the device has a connection.
Incremental Updates
Map data downloaded by specifying a bounding box or a route can be updated to the latest version using NMAMapLoader
APIs. Map data version is consistent for all map data across the entire system, whether the map data is downloaded or not. It is not possible to have some data from one map version and some from another version simultaneously in the cache. Therefore, it is important to keep the map version of the system up to date.
You can perform incremental updates if you are updating to the latest map data release from the two previous releases. Incremental updates are typically small downloads, as only the changes are downloaded. For example, when updating to the Q1 2018 map data release from the Q4 2017 or Q3 2017 release, an incremental update or patch is used. Where a patch is not available (such as updating from Q2 2017 to Q1 2018), using the NMAMapLoader
APIs to update to the latest version results in the removal of all downloaded map data, whether the data was downloaded on-demand or by specifying a bounding box/route.
Data Groups
Map packages are made up of several groups, each of which contains a different type of map data. Some of these groups may be selected or deselected before map packages are downloaded for offline use, depending on the needs of the application. The optional data groups are given in the NMAMapDataGroup
enum. To select or deselect a data group for download, pass the appropriate enum value to the NMAMapLoader selectDataGroup:
or deselectDataGroup:
method. The isDataGroupSelected:
method can be used to query the current selection state of a data group.