Description

This "3D atlas" can be used to generate VRML depictions for selected regions-of-interest on Mars. A Java servlet is used to build VRMLs using elevation data from the Viking-era Mars Digital Terrain Models (DTMs). The resulting elevation grid is texture-mapped using images from the Viking Mosaicked Digital Image Models (MDIMs).

MOC Images

Optionally, high-resolution images from the current Mars Global Surveyor's (MGS) Mars Orbiter Camera (MOC) can be viewed as embedded images in the Viking MDIM texture map. Currently, the available MOC imagebase consists of the first thousand or so publically-released MOC images from the Aerobraking-1, Science Phasing-1, and Science Phasing-2 orbital subphases. These images have been manually georectified with the Viking images so that geographic features will (for the most part) be aligned.

MOLA Profiles

Elevation profiles from the MGS Mars Orbiter Laser Altimeter (MOLA) may be included as well. These are shown as color-coded tracks above the terrain. This database of MOLA tracks includes all of the most recently released MOLA data (version I of the Precision Experiment Data Record products). When electing to include MOLAs, you should specify a region which does not exceed a couple of degrees on a side; otherwise, the servlet may return with an "out-of-memory" error.

Usage

3D VRML scenes can be generated for regions of interest either by "mouse-dragging" the region in the Mars map, or by entering the coordinates directly in the provided form. (A future upgrade will allow for zooming into the map for selecting a small region-of-interest with greater accuracy). When using the form, you can either 1) specify the lat/lon range (minima and maxima), or 2) enter the lat/lon center points and the region's size. You are restricted to a maximum area of 20 degrees on a side. When entering the coordinates directly, you can use the Update Viewer button to reflect your region on the map. The View VRML button will generate the VRML based on the region selection.

The Vertical Scale parameter is used for scaling the terrain height.

The Sample Interval parameter is used for subsampling the DTMs (a value of 1 uses every elevation sample, a value of 4 every 4th sample, etc.). The effective difference (e.g. between 1 and 4) isn't very obvious except perhaps in areas of high relief, but using subsampling (i.e. > 1) will have a significant impact on how large an area can be viewed; the larger the area, the higher the subsampling value should be. Specifying too large an area with too low of a subsampling value will result in sluggish performance in the VRML browser or possibly cause the browser to crash.

The VRML Basename parameter is an optional field you can use to specify a filename of your choosing (a ".wrl" suffix will be added automatically). After the VRML file is generated, you may revisit it at any time before midnight that same day (when the directory containing the VRML files are cleaned out), with the URL http://marsoweb.nas.nasa.gov:8091/mars/vrml/filename.wrl.

Click the MOLA &/or MOC boxes to include MOLA elevation profiles &/or MOC images.

When not using MOLAs, the servlet typically take 1 to 3 minutes to generate the VRML. Including MOLAs may (depending on the size of the area selected) increase the processing time by a factor of 3 to 5.

Performance Issues

Please note that the current state of VRML technology is in transition, and your experience with it may be "less than satisfying". You may find, for instance, that loading two consecutive VRML files will cause your browser (and possibly your computer) to crash. In this instance, clicking on another (non-VRML) link between two VRML invocations may alleviate the problem. We have found that VRML browsers for UNIX workstations are the most stable in this regard, and those for the Macintosh are the least stable. This situation should improve over time, and we recommend that you upgrade both your Web browser (e.g. Netscape or Internet Explorer) and your VRML browser (e.g. CosmoPlayer) when new upgrades are available.

Also, interaction with the VRML scene, particularly for large regions, may be very slow. We recommend that you make viewing changes slowly. If you've lost perspective on the scene (e.g. the terrain is out of your viewport), you can always pick the "View1" view from the viewpoint control at the left of the console to return to your initial viewpoint.

It is advisable to turn off the specular highlighting to reduce visible artifacts as well as speed up rendering time. In CosmoPlayer, this parameter can be accessed via the Performance pane in the preferences of CosmoPlayer.

Browser Requirements

Windows	IE or Netscape (v4 and above)
Macintosh	IE (v4 and above) or Netscape v6 Beta
UNIX	Netscape (v4 and above)

A VRML browser plugin is also necessary. This can be obtained via these links:

Windows	Cortona	CosmoPlayer (1)	CosmoPlayer (2)	CosmoPlayer (3)	Other VRML Browsers
Mac (OS 8/9)	Cortona	CosmoPlayer (1)	CosmoPlayer (2)	CosmoPlayer (3)	Other VRML Browsers
Mac (OS X)	Cortona
IRIX (SGI)	CosmoPlayer
Solaris (Sun)	Presenter

Macintosh OS 8/9 Users

Graphical region selection is currently not available to users running Mac OS 8/9, as the region selection applet uses a later version of Java than what this environment provides. Form-based region selection is available, however. The graphical region selection applet will be modified in the future to support this environment. Currently, for those wishing to be able to use the graphical interface (allowing "rubber-band" selection of your region-of-interest on map), it is suggested that you either use Internet Explorer and the Cortona VRML plugin, or upgrade to OS X.

Mac OS 8/9 users should allocate at least 40 Mbytes to their Web browser to properly display the VRMLs. More should be allocated if an out-of-memory error is encountered.