By standard the user can navigate to every place on the map. For some use cases this is not intended. If e.g. you have an application which visualizes the urban transportation net of a city in Germany it is hardly useful to let the user navigate to Antartic places. Sometimes technical restrictions lead to the need to restrict the possibilities. E.g. a service delivers only data between LOD 9 and 18, so it is useful to restrict the zooming with the same parameters also. Some map providers are delivering country specific information, even though it may be possible to navigate to other areas also, which will then contain only raw information as coastal lines.
The Visual Frame also defines the number of maps Visual Business works with. In general we render a pyramid of up to 4 maps over each other. As every map is one LOD below compared to the map above, it is typically 4-times as large (double size in x- as well as in y-direction). A high number of maps improves the visual effects on zooming in, when the higher layers are not yet available and it provides a farer view when inclining the map (horizon will be farer away). But of course effort is higher. Restricting the number of maps to 1 is not recommended as then the maps will flicker on all zooming steps. We recommend to keep the number of maps at 4, at least as long inclining is allowed.
A Visual Frame is a parameter of a scene and it prevents the user from leaving the specified frame. The frame is defined with the following parameters:
minLOD : Minimum LOD the user may zoom out (in terms of switching the map content)
maxLOD : Maximum LOD the user may zoom in
offsetMinLOD : Offset on which the user is able to zoom out further from minLOD, which will increase the camera distance without switching map content (default is 2)
offsetMaxLOD : Offset on which the user is able to zoom in further from maxLOD, which will decrease the camera distance without switching map content (default is 2)
minX : x coordinate of the left upper corner of the area to which the user should be restricted
minY : y coordinate of the left upper corner of the area to which the user should be restricted
maxX : x coordinate of the right lower corner of the area to which the user should be restricted
maxY : y coordinate of the right lower corner of the area to which the user should be restricted
layerDepth : Number of maps to be used (between 1 and 4)
The Visual Frame may be specified in parts. E.g. specifying the y coordinates of the area only keeps the user from navigating to the artic places or even further without destroying the possibility to navigate around the world. Specifing both x coordinates always means that round world is no more possible. Specifiying only one x coordinate is a bit strange because of round the world also.
The Visual Frame is always enforced. So if you define a Minimum LOD of 7 and you start Visual Business without specifying an Initial Start Position defined the application will autmatically zoom to LOD 7. If you specify an area the system will move to the specified area with the lowest LOD possible (might be even a higher LOD then specified in MinLOD as the area is even smaller). Pleas note that the specified offsetMinLOD (usually 2 LOD-levels) does not come into account when the minimum LOD is calculated out of a visual area as described here.
If no MinLOD and/or MaxLOD are defined in a Visual Frame, the information from the Map Providers are used (as defined by us). If a stack of at least 2 map providers is used we work with the maximum of the values. If e.g. a map is able to deliver tiles up to LOD 21 and the second layer (e.g. the Munich railway system which supports only upto LOD 18) supports less detailed tiles only, we will allow the user navigate to LOD 21, even though only the first layer will be rendered.
The left upper / right lower corner refers to the window corner points if the map is not inclined. If the user inclines the map (s)he will nevertheless see tiles on the horizon which are located outside the Visual Frame. The Visual Frame affects the behaviour on moving (it stops when reaching the border), on zooming out (it stops zooming when using the slider and it corrects the movement when using the mouse wheel zoom) and on changing the window size (LOD will be recalculated).
In this sample shwoing the Munich area all parameters but MinLOD (which is then determined automatically) are defined. As MinLOD is determined automatically, offsetMinLOD is 0. OffsetMaxLOD remains on the default of 2 LOD levels. This means you may zoom to LOD 20 (as measured by distance and visualized with slider position), but the framework will request and show LOD levels lower or equal 18 only.
"maxLOD": "18" ,
"minX" : "10.9" ,
"maxX" : "12.1" ,
"minY" : "47.7" ,
"maxY" : "48.6"
The Visual Frame feature is available from version Visual Business 2.1 onwards.