Thesis results
LeaverThesisVrmlTerrainMBNMS.pdf
(886 KB)
MBNMS VRML model
2000m/Trees/mbnms.wrl
Overview
The VRML terrain model of the Monterey Bay National Marine Sanctuary
(MBNMS) is the result of the collaborative efforts of Don Brutzman and
Greg Leaver of the Naval Postgraduate School, Monterey and Ray McClain
of Moss Landing Marine Labs - all in California. The project is documented
in a thesis advised by Don and authored by Greg. The terrain model consists
of numerous terrain tiles, terrain trees, and jpg images to support three
levels of topographic resolution (2000m, 1000m, and 500m). Currently,
the model uses the first version of the QuadLOD node.
Navigation
The top-level scene is a single terrain tile at 2000m resolution. A
navigation icon is positioned at the center of the tile in the screen foreground.
Navigation icons are switched in and out together with corresponding terrain
tiles. Each tile has a unique navigation icon that provides four
relative viewpoints. The initial top-level scene is at the widest
possible resolution (2000 m). The viewer can determine this by positioning
the mouse over any of the navigation icon's four compass headings.
This causes the current level of resolution (that the navigation icon is
at) to be displayed at the bottom of the browser's window. By clicking
on an icon direction label a viewpoint can be selected. Selecting
the viewpoint causes the viewer's position to change to the direction of
the compass heading chosen, at a perspective just above the navigation
icon. Navigation icons are positioned at a tile's center on the boundary
of the proximity sensor that controls the switch between resolutions.
That is, if the viewer flys beneath or drops below a navigation icon, the
next resolution for that tile will be switched in. Thus, a low-resolution
tile (and the tile's navigation icon) is replaced with four higher resolution
tiles (and their corresponding navigation icons). An icon can be
made to disappear by clicking on its sphere. Icons which have
been made to disappear can be restored by zooming out to a lower-resolution
level and then zooming back in to reload the higher- resolution level.
Georeferencing
The MBNMS Terrain Model's coordinate system is georeferenced to the
UTM coordinate system. The model is built with the VRML coordinate
system origin (the point 0,0,0 of the root node) corresponding to the baseline
position of Zone 10 of the UTM coordinate system, i.e., 0 m North, 0 m
East of Zone 10. The northwest corner of the real MBNMS is located
at 4,200,000 m north and 460,000 m east (in UTM, 4,200,000N, 460,000E)
of the zone 10 baseline. In VRML, the Terrain Model is designed so
that North is in the positive x direction, and East is in the positive
z direction. So, the northwest corner of the Terrain Model is located
4,200,000 units in the positive x direction, and 460,000 units in the positive
z direction. Thus, in the x-z plane, the coordinates of the Terrain Model
correspond to the real life sanctuary in terms of the UTM coordinate system.
The y-axis represents depth.
Limitations
Currently, the MBNMS Terrain Model can be accessed by any VRML browser.
However, going past the top-level low-resolution (2000m post-spacing) entry
file is only possible using a PC or Macintosh. This is because the
model uses Script nodes that interface with Java class files. Currently,
only VRML browsers designed for PCs follow the VRML 97 specification as
it pertains to Java in Script nodes. Therefore, the model currently
does not show higher-resolution tiles with Cosmo Player under IRIX (SGI)
because it does not support Java in the Script node. This limitation
is expected to be temporary since all VRML used in the MBNMS model is compliant
with the VRML 97 specification. Also, the on-line version of the
model seems to hang under Windows NT. Therefore it is recommended
that the model be run locally if running under Windows NT.
Greg Leaver
NPS Monterey
Updated 9/28/98
Project point of contact: Don Brutzman brutzman@nps.navy.mil