Distribution of Plants on Terrain

Possible ways to describe plant distribution

• Using a coverage bitmap
  • discretely - type information per element of the elevation grid, or any overlapping grid
  • pro: easy to draw in a paint program, easy to vary density
  • con: doesn't work well for fine boundaries, e.g. along the edge of a road
• Polygonal areas
  • structured - polygonal bounding regions indicate areas of plant coverage
  • pro: more precise placement, works well for crops
  • con: would have to create graphical tool for defining the areas, or rely entirely on existing polygonal data sources
• also need the ability to place individual trees, and/or lines of trees (e.g. along a road or fence)
• many academic papers cover the subject of producing plant distributions, such as with algorithms which simulate ecosystems - see Plant Papers

Sources of Data

• USGS LULC (land use and land cover) files
  • includes classification code such as "Herbaceous Rangeland" and "Evergreen Forest Land" which very roughly description vegetation type
  • U.S. only
• USGS Global Land Cover Characterization
  • huge raster files, in a raw format, with 1km coverage of the whole earth
  • has much better classification than LULC, example of a single type: "Needleleaf Forest (Western Hemlock, Sitka Spruce, Douglas Fir)"
  • the main drawback is the very low resolution (1km) which makes it useless for visualization at a human scale
• European Space Agency (ESA) Ionia GlobCover
  • GlobCover Land Cover V2.3 (Dec. 2010) is the highest resolution (300 meters) Global Land Cover product ever produced. Based on ENVISAT MERIS data at full resolution covering 2 periods: December 2004 - June 2006 and January - December 2009.  Labeled according to the UN Land Cover Classification System.
  • Version 2 was a 436 MB GeoTIFF file.
• The GLCF has global vegetation data
  • Tree Cover Continuous Fields
    • based on 1km AVHRR satellite data
  • MODIS Vegetation Continuous Fields
    • percent tree canopy cover, gathered 2000 - 2001, from the MODIS satellite data
• USGS NLCD (National Land Cover Database)
  • NLCD 1992 is a 30-meter land-cover classification (21 classes) based on an unsupervised clustering algorithm run on LandSat data
  • distributed as huge files, raw, 1-byte, in Albers projection, or as GeoTIFF
  • the The Multi-Resolution Land Characteristics (MRLC) Consortium is working on a newer version, NLCD 2001
• WWF Ecoregions is an amazing global map of ecoregions
  • the map data is available (25 MB zipped Shapefile), only requires submitting an email address
• USDA vegetation maps?  7.5-Minute DLG Vegetation Overlay?
• a great many people in the GIS field use polygonal areas with attributes (e.g. in a Shapefile) to describe vegetation coverage
  • unfortunately, there are no standards for the number and meaning of the attributes
  • therefore, there is almost never a consistent way to exploit these data sources, or to exchange data
• OpenTreeMap
  • A set of web software (built on Geoserver, Django, PostGIS, etc.) which provides a front-end to a GIS dataset of individual trees in a city, in use in San Francisco and Philadelphia as of 2011
  • Has a standard set of attributes per tree, including species name, location, height
  • Can export tree lists as KML or CSV files

Classification of Vegetation

• there is very little standardization
• some people treat classification of vegetation as a subset of general land-use classification (e.g. the USGS and USDA) but this does not well describe either the physical appearance or the scientific description, e.g. species
• one fairly common physical measure of trees in the forestry industry is their radius
  • this is usually stated as "Diameter at Breast Height" (DBH)
  • see Simplified guide to measuring DBH
• "There are some standards, but surprisingly few, and almost always non-visual. Some ecologists have worked on structural vegetation classifications, since it turns out that structure is very important to birds, for instance. But from what I've seen, this is usually for trees only, mostly based on age, "site class" (soils/slope/aspect), and DBH. I've never seen anything which would cross-walk a meadow from Siberia to Florida. You might get part of the way there with a structural description of vegetation form ranges (bounding sphere x age?), plus geographic range (by bioregion?). You could then pick the closest vegetation form from the closest broad bioregion. If you are in a forest in the NE but have no trees for that area, fallback might be trees of same size from a Michigan forest." - Michael Flaxman

Descriptions of Plant Distribution

• GENETICS Automated Vegetation Generation
  • part of an academic project in 2005, describing how to use terrain slope and land cover classification (LCC) to distribute vegetation
  • it was later rolled into the Delta3D engine - for programmers, see the VegetationDecorator class and their tutorial
• ECOSim - Ecosystem Simulation: site is no longer online, but available as a textbook (in French), COQUILLARD P., HILL D. Modélisation et Simulation des Ecosystèmes, 1997
• The VTP software includes distribution of vegetation - see VTBuilder Vegetation Layers

Game Programming:

• "We simply have the artists create a density map for the terrain and then randomly (with a seed) place/ render vegetation depending on the density map. Then between min and max distance we either shrink objects to size 0 or fade them out using alpha. This approach works fine for small stuff like grass or ferns." - Daniel Vogel, Epic Games