Terrain

The Aeliom Portal
Aeliom allows real time generation, rendering, illumination, and exploration of 3d virtual landscapes.
http://www.iluac.com/aeliom/

Atlas - The FlightGear mapping utility
Produce and display charts of the world for users of FlightGear, an open source flight simulator. Includes map creator and atlas viewer. Can also be used stand alone. Under development, GPL. [Win32(cygwin),Linux]
http://atlas.sourceforge.net/

Blueberry3D
A program for designing and creating virtual landscapes utilizing real map data or synthetic data from fractals. Fractals are also used to dynamically extend the data and level of detail. [Win 98/SE/Me/2k]
http://www.blueberry3d.com/

3DEM
Interactive OpenGL 3D viewer with flyby and animation capabilities. Reads most familiar US DEM formats and can export to common image and terrain formats. [Win95/98/ME/2000]
http://www.visualizationsoftware.com/3dem.html

Generating Terrain
An older (1996) collection of documentation, source code, and programs for generating and visualizing terrain.
http://www.geocities.com/Area51/6902/terrain.html

G-Graphix
Makers of G-Vista, G-Scene, G-Render Library, software components for CD-ROM/DVD-ROM/Web-productions to interactively fly over huge contiguous terrains. Target market: high end professional.
http://www.g-graphix.de/english/home/index.htm

Height Map Editor
Free program that edits, generates, and manipulates terrain height maps. These can be used in terrain renders, which are used in games, applications, and demos. Web base manual available. [Windows and Linux]
http://hme.sourceforge.net/

InReality (tm) Model Viewer
Visualization tool that permits the user to view RealSite (tm) models within a virtual environment. [IRIX, Win32]
http://www.govcomm.harris.com/realsite/

KLevel Heightfield Tool
A heightfield modelling tool designed to mimic Leveller for Windows. It features an OpenGL preview and many brush-like tools. (free, with code) [Linux]
http://sourceforge.net/projects/klevel/

Landsraad
Alpha version of a terrain editor/viewer for BeOS.
http://www.geocities.com/stratgis/landsraad/index.html

Leveller by Daylon Graphics
Heightfield, bumpmap, and terrain modeler for Windows. Has an active user community with many 3rd party plugins. Downloadable demo with limited functionality.
http://www.daylongraphics.com/products/leveller/index.htm

Mapper
Earth data processing and visualization system. It can combine data from different sources and in varying formats to a single view. It is not an image processing tool but rather builds a 3dimensional model of the earth. [Win95/NT] 1997
http://www.geocities.com/TimesSquare/1658/mapper.html

MapRender3D
Modeling and visualization software package that creates relief maps in both 2D and 3D using either proprietary global elevation database or public domain DEMs. Features include projections, texture draping, lighting, shading, and elevation color graduation.
http://www.maprender3d.com/

Natural Scene Designer
Raytracing based landscape renderer with object (trees, rocks, lakes) creation, placement and animation capabilities. Interactive planimetric, and 3D modeling viewpoints. Imports USGS and STDS DEMs. [Windows and Mac]
http://naturalgfx.com/

nineteen70five
Specializes in the import of GIS data sets and creation of a GIS viewer, which allows the user to "fly" over a 3-D image of their data sets.
http://mzone.mweb.co.za/residents/jhammes/main.htm

OBVIO
A free win32 3D viewer which demonstrates Dynamic Level of Detail (DLOD), based on OpenGL and GLUT, only reads USGS DEMs. Appears to be in active development.
http://www.geo-visualisierung.de/demo.htm

OpenGL Terrain Engine
An experimental OpenGL interactive terrain viewer with surface textures, clouds and reflective water capabilities. (free, with code) [Win32]
http://ohad.visual-i.com/exper/exper.htm

OpenSkies Training System
Free authoring tool for virtual environment training system. A low cost PC-based system which incorporates trainee performance measurement capability. [Win9x/NT/2k]
http://www.openskies.net/training/index.html

Skyline Software System
A complete, modular software collection to serve photo-based 3D interactive environments over the internet or intranets. (free, no code) [Win9x/NT/2k]
http://www.skylinesoft.com/corporate/corporate_home.asp

SpatialAce
Toolkit for building interactive real-time applications with 2D or 3D presentations, from simulators and command and control (C3I) to surveillance and traditional GIS systems. [Win9x/NT/2k]
http://www.spatialace.com/

TechNature Library
A collection of rendering, mathematics, and texturing functions that use fractals to "grow" everything from plants to planets with seamless procedural textures. (shareware, with source code) [Requires DirectX 6.0+]
http://www.tanzanite.to/

UrbanModeller
Software for visualisation of non-tangible data related to the urban environment. It may be used to construct 3D thematic 'maps' such as land use. A component of the Virtual Field Course from the U. of Leicester. [Win9x/NT/2k]
http://www.geog.le.ac.uk/vfc/software/urbanmodeller/index.html

Virtual Terrain Project
Promotes development of tools for constructing any part of the real world in interactive, 3D digital form. CAD, GIS, visual simulation, surveying and remote sensing. (free, with code) [win32, unix]
http://vterrain.org/

VistaPro
Create 3D landscapes using real-world data from the United States Geological Survey and extra-terrestrial data from NASA. [Win9x+]
http://www.vendornation.com/*ws4d-db-query-QuickShow?vp001

Wilbur
Small program for playing with terrain data (height fields). Imports data from and to many popular file formats. Can use a number of image processing operations and height field painting tools. (Free, no code) [Win9x/NT]
http://www.ridgecrest.ca.us/~jslayton/software.html

World Construction Set
Professional photorealistic terrain modeling, visualization, rendering and animation program. Create stunning, photorealistic images and animations with image object rendering. [Win9x/NT/2k/Mac/SGI]
http://www.3dnature.com/index.html

WorldPerfect
A standalone Windows desktop utility for generating high resolution terrain databases from photo-realistic imagery, digital elevation data, and cultural feature content.
http://www.metavr.com/products/worldperfect/worldperfect.html