VR MAPPING VERSION 4 – Stereo Roaming

Description

The method for displaying stereo images when roaming in VrTwo has changed in Vr Mapping version 4.

In previous versions of VrTwo, entire strips of imagery were buffered in the x direction. Although this resulted in fast roaming speeds it required a large amount of memory. The method of buffer storage in version 4 is now a tiled method that results in smooth roaming but uses less memory.

Why the Change?

With existing and upcoming additions to Vr Mapping, a smaller memory footprint was needed. Following are several reasons for the change.

Version 4 includes an option that supports stereo data collection using the Leica ADS40 Airborne Digital Sensor. This sensor required the display of images that are very long in the x direction. The tiled format is better suited for this type of imagery and other satellite stereo imagery. Future versions of VrTwo will include options for the support of stereo from various satellite sensors.

Future releases of Vr Mapping will include improved support for LIDAR data storage and processing. It is essential that the LIDAR points are displayed in stereo when roaming and a smaller image memory footprint is needed when displaying this large amount of points.

Digital Terrain Modeling (DTM) and stereo roaming both compete for memory. Large, complex DTM models could cause memory problems and the reduction of memory usage by stereo made these two applications less competitive when grabbing memory.

With the popularity of smaller format cameras such as the Microsoft UltraCam, stereo data collection by model is becoming less practical. Future releases of VrTwo will include the ability to manually or automatically switch between stereo models without the termination of active mapping application. The new tiled method is faster when loading the initial image data when switching models.

Controlling Memory Usage

The amount of memory that will be used when roaming in VrTwo may be set by the user in the Vr Configuration Program in Configuration under Image Graphics.

The two primary parameters determining memory usage are the Number of Tile Buffers X and Number of Tile Buffers Y. This is the number of tiles that will be loaded around the current stereo view window and can be from three to nine buffers in the x and y direction. For example, setting these numbers to 5 and 5 would allocate 25 memory buffers.

If performing other memory intensive tasks such as DTM processing then these numbers should be smaller. The user should experiment with these buffer numbers to determine the best values for most mapping tasks to be performed.

The Maximum Roam Levels controls the amount of zoom levels that are kept in memory. Each zoom level consumes memory so this parameter should be set as low as possible. Setting this number to a low value does not prevent zooming to any level, but will cause a slight delay when zooming to levels that are not in memory.

The Maximum Roam Full Graphics Level determines what zoom levels will display full graphics such as line fonts and splined lines. Any zoom level higher than this value will ignore line fonts and splining, resulting in faster display and less memory consumption at higher zoom levels.

What Changes are needed to Run Version 4?

The most efficient image format for the epipolar images for VrTwo version 4 roaming is now the tiled format. Previous versions of VrTwo were optimized when using a scanline image format.

Version 4 of the VrTwo Orientation program includes the Image Tile Size option when creating epipolar images. This value should be set at 128 and the Image Compression Ratio should be set at 0. The user can experiment with other tile sizes such as 512 to see if performance is improved for your computer. Our testing has shown that a tile size of 128 is optimal.

To maximize performance for existing epipolar images these images should be converted from scanline format to the tiled format. This can be performed on an entire job in a batch mode from the Vr Image Utility program from the Misc menu, under Convert Images. Following are the sample settings for the conversion from scanline format to tiled format.