Introduction to GIS Spatial and 3D Analysis Lecture Notes PDF

Introduction to GIS { Spatial and 3D analysis Presentation outline o Spatial analysis o Overlay techniques o Proximity analysis o Interpolation o Euclidean distance o 3D models and DTM surfaces o 3D analysis  Spatial Analysis  By using the G...

Introduction to GIS { Spatial and 3D analysis Presentation outline o Spatial analysis o Overlay techniques o Proximity analysis o Interpolation o Euclidean distance o 3D models and DTM surfaces o 3D analysis  Spatial Analysis  By using the GIS as a computerised map, controllers of police vehicles and ambulances can instantly call up a detailed map of the area around an incident.  By tracking the vehicles in real time and using route-finding GIS functions, the controller can identify the best vehicle to attend the emergency and provide it with directions to follow the fastest way to the incident.  Historical information can be stored and later used to analyzed for the pattern of incidents and black spots. Emergency Services  Overlay Techniques  Placing map layers on top of each other  Looking at multiple map layers and selecting objects from one layer that lie within an object from another layer  Conduct overlay operations by combining layers of data to create one new layer Thematic Overlays Social, economic factors Economic & industrial factor Transport & utility factors Land use factors Administrative factors Environmental factors  Cont. Overlay for optimum rice growing areas  Optimum rainfall required for high yield is 10mm/d  Soil type required is sandy loam  By combining the rainfall map and the soil type map it is much easier to find the best location.  Numeric value can be assigned to the amount of rainfall and each soil type. This makes it easier, on the resulting map, to see where the optimum growing area is located Overlay operation  Cont. Overlay  Results are only as accurate as the data that was used for the query.  Spatial querying is used in many different ways to help understand the world around us.  Often the answer to a particular problem can only be revealed by comparing two layers of information in a way that would be almost impossible to achieve without the GIS software. Overlay operation  Proximity Analysis Proximity analysis allows you to Buffer with Multiple Ring buffers selected features that fall with a specified distance range. The area of intersection between all three buffers will approximate an area of common interest. Proximity Analysis can be applies and performed in many contexts depending on Intersection is the common area the problem under study.  Interpolation Interpolation allows you to create a surface from point values of concentration/ magnitude outward over a given area or area of interest Spatial interpolation  A process of creating a surface based on values at isolated sample points.  Sample points are locations recorded spatial coordinates where data is collected on some phenomenon  Spatial interpolation uses mathematical estimation to “guess at” what the values are “in between” those points  Output can be created in either a raster or vector interpolated surface  Interpolation is used because field data are expensive to collect, and can’t be collected everywhere  Eg. Interpolation  Ground water pollution samples  Can interpolates a raster surface from points using an Inverse Distance Weighted (IDW) and many other interpolation techniques.  Can also used the interpolation surface to create contours After Interpolation Grd H20 sample points DWI Interpolation Contour Interpolation Eg. 3D interpolated surface  Euclidean Distance The Euclidean Distance is used to find the nearest point or area of interest Eg. a hospital for an emergency helicopter flight. It can be used when creating a suitability map, when data representing the distance from a certain object is needed ie. roads, towns, any feature of interest on a map Distant area from the roads  3D Models and surface analysis  To understand a two-dimensional (2-D) representation of the real landscape you need a level of interpretation and imagination  The physical world exists in three dimensions even though the realm of conventional maps are uncompromisingly flat  The capability of GIS to produce dynamic and attractive three-dimensional (3-D) maps is one of its most exciting benefits.  Height Information  Map makers use a range of visual symbols to show height information and create the illusion of an undulating surface:  Contours  Spot height symbols  Hill shading  Cliff and slope symbols  Viewpoint symbols  Capture of height information  Height information can be captured in a GIS in exactly the same way as the shape and location of objects.  The spectacular ability of today's computers to perform calculations means that 3-D models of the ground surface can be constructed from data recording the height at different points across an area.  The typical way this information is stored is an extension of the conventional grid coordinate system: as well as recording the latitude (the x axis) and longitude (the y axis) for a given point, the elevation (the z axis – usually as height above sea level in meters) is also stored.  Height information for an area is often referred to in terms of z values.  The fluctuations in ground height across an area are a continuous phenomenon – every point on the ground has a Z value irrespective of whatever physical features are present Data models used for DTM in GIS  Spot height/LIDAR data  Contour  Grid  DEM Basic data structures for elevation Vector Elevation Data Structure Spot height/ LIDAR data Contour lines  Raster Elevation Data Structure Grid DEM (digital elevation model) Two ways of representing elevation: Vector contour lines Raster grid With grids, you can perform several types of analysis that are impossible with contour lines  Two ways GIS works with digital elevation data Spatial Analyst - 2 Dimensional 3D Analyst - 3 Dimensional Methods of interpolation elevation surface TIN Voronoi Diagrams Cont: IDW (Inverse distance weighted) Kriging Cont: Topogrid Surf (RST) Regularized Spline with Tension  Developing a DTM ( Digital Terrain Model)  Point height information  Points of the same height joined to form contour.  3-D GIS data is stored as a grid of points  x, y and z values are stored as attributes, referred to as DTM or DEM.  From the grid a computer builds a surface to form a 3-D model. TIN Surface  Representing a surface is to create a TIN  A TIN model forms a continuous surface by connecting irregularly spaced spot heights to form triangles, keeping a flat surface within each triangle. TIN (Triangulated Irregular Network)  3D Surface Analysis Create contours  3D Modeling 2D Model TIN surface Slope derivation Slope Surface analysis Slope Surface analysis Aspect derivation Aspect Surface analysis Hillshade derivation Hillshade Surface analysis Hill shade surface analysis Viewshed Surface analysis 3D model Buildings and Roads (Perspective Viewing)  Realistic 3D Models  These 3-D models can be made to look very realistic by applying colour to the surfaces  Drape raster images of maps or aerial photos over the surface this gives a stunning realistic effect  Buildings, forests and electricity pylons with known Z values can be built into the 3-D model  3D computer models of entire towns and villages can be built to relate directly to the real world Realistic 3D models  Terrain with Spatial Modeling Analysis Erosion and deposition Elevation and rainfall  Summary  By using GIS and overlay techniques many hidden pattern with in data can be revealed  Techniques such as buffering can be used to define boundaries with which a phenomena occurs and related to other phenomena on different data  Overlay operations can be used to develop and selection suitable site for different activities  Proximity techniques together with geoprocessing tolls can be used to identify an area of equal interests from many given points  Interpolation is an effective techniques to spatially estimate concentrated value across a given surface. and Euclidean distance techniques create uniform measure of distance from an area of interest.  Both vector and raster can be used for 3d models. 3D surfaces allows the visualization of terrain model and analysis of slope, hillshade, aspect, veiewshed etc