4.3 Technical Framework RequirementsTop4.1 Objectives4.2 Functionality



4.2 Functionality

At this point the conceptualized animated zooming scale model is introduced in detail. The discussion starts with a description of the full zooming process using a zoom slider, followed by a description of the special features of the ZoomOut process.
Suppose Zn is the current zoom level of the main map, Zmax the maximum ZoomIn level, and Zmin = 0 as the minimum ZoomOutlevel, for which the following applies:
Z ∈ N and Zmin ≤ Zn ≤ Zmax

The following steps describe the developed scaling model as well as the exact process involved in using the zoom slider. A state diagram (Figure 4.2) and an activity diagram (Figure 4.2) illustrate this model. The individual steps involved are referenced by the numbers contained in the processes of the activity diagram:

  1. The user points the mouse on the zoom slider, presses and holds down the left mouse key. As soon as he/she releases the key, the process is stopped and completed with Step 8.
  2. The current zoom level Zn is determined.
  3. All tiles k within zoom level Zn, which are fully or partially located in the visible area, as well as all pre-loaded tiles which border on this area, are determined.
  4. The user decides on a zoom direction (ZoomIn or ZoomOut).
  5. At this point the compatibility of the decision made in (4) with the current zoom level Zi (in the first round Zi = Zn) is verified, ie. if Zi = Zmin, respectively Zi = Zmax, then ZoomOut or ZoomIn is not possible. In this case, a new zoom direction must be selected (Step 4). Otherwise the process continues with step (6).
  6. The corresponding zoom-scale process occurs in tandem with the zoom slider operation (in the direction chosen in (4)):
  7. As long as the left mouse key is held down (see Step 1), the user can change the zoom direction at any time, which brings the process back to (4). Once the mouse key is released, the zoom process is completed with (8).
  8. The visible area is redrawn in the new zoom level Zi including all required tiles (using standard tile size K(Zn)). In addition (according to the principles outlined in the tiling method; see Section 2.3.5), all adjacent non-visible tiles are preloaded at the same size. This completes the zoom process.
State Diagram of Zoom Process Using Slider

Activity Diagram of Zoom Process Using Slider

Special Considerations for ZoomOut

Two solutions regarding the preloading of tiles in Steps 6e of the zoom process are introduced. The objective is to ensure quick tile loading (ie. without delay) and thereby eliminate the creation of a white border around a now smaller map.

© June 1, 2007 | Emanuel Schütze | some rights reserved.
This work is licensed under the Creative Commons License Attribution-ShareAlike 2.0 Germany.

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