Using Load-On-Demand

Maps > Using Load-On-Demand

This chapter explains how to use the load-on-demand mechanism, which lets you load into memory only the data that you want to display in a manager view and unload the data when you no longer use it. This mechanism is extremely valuable, especially when very large maps are concerned. Let us consider a database storing maps of the whole world with a scale of 1/25,000. If these maps were scanned with a resolution of 300 DPI, the required storage space would be as follows:

654 kilobytes for 1 square kilometer

64 megabytes for 100 square kilometers

Approximately 310 terabytes for the whole world

Given the volume of the data, it is crucial to have a load-on-demand mechanism that will load and display only the portion of a map of direct interest.

This chapter covers the following topics:

How Load-on-Demand Works introduces the load-on-demand classes and how they are related.

Structure and Size of the Tiling Grid describes the tiling parameters.

Displaying the State of Tiles explains how to use the debug view to display the state of tiles when implementing load-on-demand for a new format.

The following code associates an IlvManagerMagViewInteractor to the debug view. It introduces the various means you can use to control load-on-demand.

Managing Errors and Load-on-Demand Events describes how to manage errors and events related to load-on-demand.

Caching Tiles introduces the tile caching mechanism.

Saving a Tiled Layer presents issues related to saving tiled layers.

Writing a New Cache Algorithm illustrates through an example how to write a customized cache algorithm.

Implementing Load-on-Demand for a New Data Source explains how to implement a new tile loader.

Load-on-demand implementations for predefined map readers are described in Chapter 5, Predefined Readers.

Version 5.8