Understanding cache management in ArcGlobe

There are two types of caching used by ArcGlobe: memory caching and disk caching.

Memory caching refers to assigning an amount of physical memory (RAM) for use by ArcGlobe. For optimum performance you can set the amount of memory assigned for each type of data used. For example, if your 3D view contains many elevation data sources and very few 3D features, you can allocate more RAM for the elevation layers. Often, an ArcGlobe document that is performing poorly can become very interactive through well-defined memory cache settings.

Disk caching creates a temporary file, or cache, for each layer in ArcGlobe that helps you display and navigate your data efficiently. A disk cache stores the data and information that allows ArcGlobe to better manage your environment by controlling levels of detail. The status of a cache can be on demand, partial (containing some details of the layer), or full (containing all the details the layer has to offer). As you navigate your layers in ArcGlobe, the parts of the data you zoom to are cached on demand to disk. Revisiting these areas subsequent times will be faster because they are already cached. In addition, it's possible to generate a partial or full cache as a batch process. This is beneficial if you need ArcGlobe to display any area at a specified level of detail (partial cache) as fast as possible or any area at the highest level of detail as fast as possible—for example, when giving demonstrations to an audience. The name of a layer's disk cache is a concatenation of its display name and global unique identifer (GUID). Saving the ArcGlobe document or creating a layer file will ensure that the disk cache is not inadvertently deleted, as well as retain a link to the cache for future use. When the display for a layer changes, its disk cache is automatically deleted and recalculated. You can manually delete the entire disk cache for a layer by right-clicking it in the table of contents and clicking Refresh. This is useful for temporal layers, such as weather data. You can also partially refresh a disk cache, where a spatial extent is used to remove a subset of the cache. This is useful when a subset of the source data has been updated, such as an edit to a road network.

A variety of disk cache management options are available, allowing you to delete caches on layer removal or exit, delete caches as space is needed, and set the size and location of the ArcGlobe cache folder. You can also manage existing cache data using the ArcGlobe Deployment wizard.

When should I manually generate a disk cache?

Usually, the best option is to allow ArcGlobe to automatically cache the common areas of your data. Navigating ArcGlobe will build an on-demand cache, where the places you visit (and may visit again) will become part of the cache, but places you never visit don't become part of the cache. This will keep the amount of disk space used to a minimum. A consequence of an on-demand cache is a slightly increased time to display and cache new places.

An alternative to the on-demand cache is to build a partial cache for the layer. This process makes a cache of the entire layer but only for a specified range of detail. This option is the best alternative for optimizing layers that have distance thresholds for visibility and are visited in many locations.

A third alternative is building a full cache for the layer. This process makes a cache of the entire layer at all supported levels of detail. If you want the highest resolution of the data available in the shortest amount of navigation time for any potential region of the data, creating a full cache of the data may be the best alternative.

The possibility of long processing times and increased disk space requirements make partial and full caching a secondary option to on-demand caching. Evaluate whether you need quick access to a relatively small number of areas, whether you work with all areas at a specified level of detail, or whether you need quick access to all areas at their highest level of detail.

Disconnected caches

A disconnected cache is the on-disk cache of a layer that is disconnected from the source data. A disconnected cache contains visualization information, which can be used to display the data in ArcGlobe. You should disconnect a cache only after building a full data cache using the Generate Data cache command in ArcGlobe. This is because the source data can no longer be referenced to fill in any gaps in the display.

A disconnected cache should be used for visualization purposes only, as it does not support GIS-based functionality such as Identify, Find, and Selection, or access to the features' attribute data. A disconnected cache can be accessed via the layer file found within the cache folder. During data cache building this layer file will be saved in the cache folder by the ArcGlobe application. You should use this layer file to load a disconnected data cache into ArcGlobe.

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