Rasters

Steve Signell, Instructor (signes@rpi.edu)Robert Poirier, TA (poirir@rpi.edu)

School of ScienceRensselaer Polytechnic Institute

Monday, February 2, 2014

GIS in the SciencesERTH 4750 (38031)

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

• 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

Reality

Regulartessellation

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,

LiDAR, and more

National Elevation Dataset

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

National Elevation Dataset

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

National Elevation Dataset

• LiDAR (Lilight, DARradar)• 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://

landcover-modeling.cr.usgs.gov/index.php

Questions?

21

5 min break

Part II

22

Demos & details