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Declaration:property CacheMagLimit: double;

TGeoMap provides a caching mechanism to speed up the display of reduced maps. This mechanism creates a reduced map image in memory if the magnification factor of the map is set below the value of CacheMagLimit. Thus the subsequent accesses to the reduced map are accelerated considerably.

However, there is a trade-off between gain in speed and required additional memory. Setting the property CacheMagLimit to high values will allocate considerably more memory (in theory, with CacheMagLimit set to 1.0 the caching mechanism would allocated an additional amount of memory which equals the amount of the original map - which could be several hundred MBytes). The amount of additional memory can be calculated according to the following equation:

Additional Amount = Original Requirements * sqr(CacheMagLimit);

The property CacheMagLimit can be set to values between 0 and 2/3. Values outside this range will be automatically restricted to this interval. Setting CacheMagLimit to 0 turns off caching. By default, CacheMagLimit is set to 2/3 (which means a maximum allocation of additional memory in the range of 45% of the original map requirements).

Hint 1: There is no need for caching for small maps (e.g. maps below a size of 2000x2000 pixels). Thus you should turn off caching for small maps if memory allocation is an issue.

Hint 2: Please note that there is no need for caching if the magnification factor is greater than one, since any map operation with zoom factors above 1.0 accesses always a smaller portion than the entire map - which is automatically faster.

Last Update: 2017-May-21