GIS in the Sciences ERTH 4750 38031 Rasters

GIS in the Sciences ERTH 4750 (38031) Rasters Steve Signell, Instructor (signes@rpi. edu) Robert Poirier, TA (poirir@rpi. edu) School of Science Rensselaer Polytechnic Institute Monday, February 2, 2014

Rasters

Rasters • Rasters are tesselations • A tessellation is a partition of space into mutually exclusive cells that together make up the complete study area • There are two groups of tessellations: – Regular tessellations, the cells are the same shape and size – Irregular tessellations, the cells vary in shape and size

Regular tessellations Reality Regular tessellation • All regular tessellations have in common that the cells are of the same shape and size, and the field attribute value assigned to a cell is associated with the entire area occupied by the cell

Irregular tesselations • Triangulated Irregular Networks (TIN) • Each plane fitted through three anchor points has a fixed gradient (Slope)

Raster types Two major types of raster data: • Continuous • Discrete, or ‘thematic’ National Elevation Dataset (NED) National Land Cover Dataset (NLCD

Resolution & Scale • The size of the area that a single raster cell represents is called the raster’s resolution • Independent of scale

Resolution & Scale

Zones & Regions • Zone: Any two or more cells with the same value belong to the same zone • Region: Each group of connected cells in a zone is considered a region

Continuous Rasters • Digital Elevation Model (DEM) • National Elevation Dataset (NED)

National Elevation Dataset • primary elevation data product of the USGS • Seamless for US and territories • Compiled from contour maps, remote sensing: SRTM, Li. DAR, and more

National Elevation Dataset • • USGS contour maps Resolution: 10 -30 m Not emperical Quality varies by surveyor/map

National Elevation Dataset • Shuttle Radar Terrain Model (SRTM) • Resolution: 30 m • Holes

National Elevation Dataset • Li. DAR (Li light, DAR radar) • High Resolution (sub cm) • Multiple returns

National Elevation Dataset • Updated regularly to reflect better data, changes in the landscape

National Elevation Dataset Terrain Modeling

National Land Cover Dataset Land Classification

National Land Cover Dataset • NLCD derived from Landsat, a series of multi-spectral remote sensing satellites.

National Land Cover Dataset • Landsat 8 & 7 • Multispectral ( Infrared- UV) • New data every 8 days • http: //landsat. usgs. gov/gallery. php

National Land Cover Dataset • Every ~ 5 -10 years • http: //www. mrlc. gov/ • http: //landcovermodeling. cr. usgs. gov/index. php

Questions? 5 min break 21

Part II Demos & details 22