Event definitions can contain the URL of an image file. The file can be one of several common image formats including jpeg, png, bmp, wbmp, tiff, and gif. The images are drawn within the event's outline so they will scale with the display size of an event.

loading images


Loading many images from a remote server

Images can take a long time to load and display the first time, particularly if they are loaded over a slow network connection. The QViewer has the added challenge of occasionally being asked to show hundreds or thousands of images, some of them very small, and sometimes partially or completely overlapped by nearer images. The QViewer tries very hard to decide which images are most important to the display by computing which ones take more screen pixels to draw from the current viewpoint. The important ones are fetched first. However, the QViewer does not wait for each image file download to complete. Images not yet loaded are displayed as a rectangle of a light color. When the image download is complete, the display area is redrawn with the new image. This preserves much of the speed of interactive movement. Loaded images are cached on the user's disk.

images in endcuts

Images in endcuts are always handled by extensions. The images can be generated by the extension itself, or loaded from files containing known image types.


Images in endcuts

Some events represent values that change continuously with time. An event extension can display a representation of that value in its endcut. The endcut is the rectangle in which the category containing the event intersects the display time. An example of a continuous time function is contained in the moon phase extension. A picture of the moon's phase at the QViewer's display time is generated and displayed in the endcut.

Endcut display is also useful in cases where there is a different image for a sequence of times intervals. An example is an event that shows images of all the front pages of a daily newspaper. Rather than loading images (perhaps hundreds or thousands, depending on the time scale) and displaying only one small edge of most of them, only the one associated with the display time needs to be loaded in the endcut. This can be done relatively quickly and preserves interactive display speed.


A third-party library that supports SVG (Scalable Vector Graphics) is included with the QViewer. This library is capable of fast rendering but is not feature-complete and will not accept all SVG files. SVG files cannot be attached to events like other image file types, but must be drawn with an extension.

The MapSVG draws a SVG file in the endcut. The MapSVGRegion extension works with the image loaded by MapSVG to allow an event to assign a color to SVG elements, such as states or countries on a map, while the display time is between an event's start and end times.

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