INDEX

### NVIZ - Description

nviz is meant to be used as a tool for viewing data surfaces in three dimensions using GRASS on Silicon Graphics IRIS computers. It evolved from the earlier GRASS program SG3d. Users familiar with SG3d will find nviz similar but with a slightly different interface and many added features. New features include the ability to visualize multiple raster, vector, and site files at one time, and the addition of volume data among others. Hardware requirements are a Z-buffer and 24 bit graphics OR a 24 bit graphic emulator, such as that on the IRIS Indigo.

nviz uses raster files as "elevation" and also as attributes of the surfaces (such as color, transparency, etc.). While a true elevation data file used as elevation will produce the most realistic surfaces, users are encouraged to be creative in selecting other types of data to be represented by the vertical dimension. Most continuous (as opposed to discrete) data types will result in a visualization that makes sense. While developing the program, we used chemical concentrations as the elevation file with good visual results.

Emphasis during development was on ease and speed of viewer positioning and flexibility for using a wide range of data values and sizes. Since a wire grid can be drawn very quickly, such a grid is used to provide real-time viewer positioning capabilities. Similarly, a lighting "model" provides real-time feedback as the user adjusts lighting. Grid and polygon resolution control allows the user to further refine drawing speed and detail as needed. Continuous scaling of elevation values from 1.0ee-7 to 1.0ee+7 provides the ability to use various data types for the vertical dimension.