Spatial & Terrain Analysis Nigel Trodd Coventry University in 3D

Aim & objectives To understand the application of 2D+ terrain analysis in GIS … improves communication & interaction … is essential for environmental modelling … drives new methods of data capture & management 3D to review methods of 2D spatial analysis to identify 1st and 2nd order derivatives of DEM data to identify advanced methods of terrain analysis

we should not rush these things without some basic spatial data modelling

dimensionality 2D 3D 2.5D Entitation points, lines, areas volumes surfaces not a problem 2D + above, below DEM, TIN, voxel Data modelling geometry topology spatial concept

Measurement of inherent properties simple geometric measurements associated with objects Point – none! Line - length, mid-point Area - perimeter, area, centroid, shape Surface – mean, min, max, range, variance Volume – volume, centroid

Spatial analysis in 2D

Definition of spatial analysis A method of analysis is spatial if the results depend on the locations of the objects being analyzed e.g. –move the objects and the results change Or –the analysis modifies geometry or creates new geometry

Spatial operators Berry, J.K., 1987, Fundamental operations in computer- assisted map analysis, International Journal of GIS Reclassifying maps Overlaying maps Proximity and connectivity Characterizing neighbourhoods

Reclassify Change or create a new entity using spatial properties Reclassify & then merge adjacent areas with the same attribute i.e. change geometry

Overlay analysis Point in Polygon Polygon on Polygon

Polygon on Polygon overlay for raster data

Proximity analysis: buffering Create a new area within a user-defined distance of an existing entity e.g., to determine areas impacted by a proposed highway

Contiguity analysis Which states share a border with Missouri?

Neighbourhood analysis Local operators calculate an output value based on the values of nearby locations Zonal operators Focal operators –the area(s) of interest is defined by another data layer –the area of interest is defined by a user-specified moving window

Focal operators output at a location calculated from the values at locations in a window

Terrain analysis in 2.5D DEM visualisations DTM 1st order derivative 2nd order derivative

1st order derivatives

2nd order derivatives

Terrain analysis watersh ed

viewshe d Terrain analysis

Summary & Conclusion 3D GIS is appealing - but rarely implemented 2.5D is frequently implemented using a surface entity type Terrain analysis in 2.5D exploits multiple visualisations of a DEM and its’ 1st and 2nd order derivatives 2.5D products make useful inputs to environmental models Much (most?) terrain analysis still relies on spatial operations in 2D