GEOG 5060 GIS Environment Lecture 4 Gridbased modelling

GEOG 5060 GIS & Environment Lecture 4. Grid-based modelling • Outline – introduction – linking models to GIS – basics of cartographic modelling – modelling in GRID Lecture 4 GEOG 5060 - GIS and Environment 1

Introduction GEOG 5060 GIS & Environment Lecture 4 • GIS provides: – comprehensive set of tools for environmental data management – limited spatial analysis functionality – but does provides framework of application • limited spatial analysis functionality may be addressed by linking models into GIS Lecture 4 GEOG 5060 - GIS and Environment 2

Spatial modelling issues GEOG 5060 GIS & Environment Lecture 4 • Model problems: – most models do not provide tools for data management and display, etc. – many models are aspatial • GIS provides: – framework of application – allows user to add spatial dimension (if not already built into the model) Lecture 4 GEOG 5060 - GIS and Environment 3

GIS-able models GEOG 5060 GIS & Environment Lecture 4 • Types of models applicable to integration with GIS include: – certain aspatial models black box models • lumped models • – all spatial models • distributed models – temporal models Lecture 4 GEOG 5060 - GIS and Environment 4

Linking models to GIS GEOG 5060 GIS & Environment Lecture 4 • Two basic methods of integrating models into the GIS framework: – soft or loose coupling • models and GIS are linked via file transfer – hard or tight coupling models and GIS are linked directly through sharing common database • model programmed using GIS macros and functions • Lecture 4 GEOG 5060 - GIS and Environment 5

Creating the link GEOG 5060 GIS & Environment Lecture 4 • How models are integrated into a GIS depends on: – the type model itself – the flexibility of the GIS as a modelling environment – the time and resources available • Fuzzy boundary between loose and tight coupling Lecture 4 GEOG 5060 - GIS and Environment 6

Loose coupling GEOG 5060 GIS & Environment Lecture 4 External data transfer MODEL G. I. S GIS database Lecture 4 GEOG 5060 - GIS and Environment 7

Tight coupling GEOG 5060 GIS & Environment Lecture 4 Internal data transfer MODEL GIS database G. I. S Lecture 4 GEOG 5060 - GIS and Environment 8

Example GEOG 5060 GIS & Environment Lecture 4 • GIS-based gas dispersion model – requirements: an emergency planning decision support system is required for accident planning involving releases of chlorine gas from chemical plants • a dense gas dispersion model needs to be linked to a GIS to enable predictions of gas dispersion to be integrated with environmental data to assist in emergency planning procedures • – loose or tight coupling? Lecture 4 GEOG 5060 - GIS and Environment 9

Questions… • • Lecture 4 GEOG 5060 GIS & Environment Lecture 4 Which model? Which GIS? Which data? What level of coupling? GEOG 5060 - GIS and Environment 10

Loose coupling approach GEOG 5060 GIS & Environment Lecture 4 1. identify point of release (POR) and conditions of release (COR) 2. input POR and COR variables to model via keyboard input 3. run model 4. pass model results to GIS via file exchange 5. create model results data layer in GIS 6. integrate (overlay) with other data layers Lecture 4 GEOG 5060 - GIS and Environment 11

Tight coupling approach GEOG 5060 GIS & Environment Lecture 4 1. identify POR and COR 2. run model • • • create POR and COR layers model accesses GIS database directly for inputs at every increment of the model run to update basis for predictions model creates new data layer in GIS database describing results 3. integrate (overlay) model results with other data layers Lecture 4 GEOG 5060 - GIS and Environment 12

Integrating GASTAR with Arc/Info Lecture 4 GEOG 5060 - GIS and Environment GEOG 5060 GIS & Environment Lecture 4 13

Modelling testing GEOG 5060 GIS & Environment Lecture 4 • Testing models – verifying model output can present certain problems for the user – especially true if : • • • Lecture 4 the model is complicated two or more models are used the data used is complex or of dubious accuracy or both! long timescales are involved the model is of the black box variety or if the user is unfamiliar with its workings GEOG 5060 - GIS and Environment 14

Example GEOG 5060 GIS & Environment Lecture 4 • RUNMOD – a lumped catchment model of the hydrological cycle lumped input: precipitation • lumped storage: soil store, groundwater store, channel store • lumped output: evapotranspiration, runoff • – parameters governing infiltration, through flow, percolation, etc. can be altered to improve modelled outputs compared to measured outputs – this is a process known as calibration Lecture 4 GEOG 5060 - GIS and Environment 15

Questions… GEOG 5060 GIS & Environment Lecture 4 • What are the advantages of model calibration? • How could this particular model be integrated into a GIS framework? Lecture 4 GEOG 5060 - GIS and Environment 16

Modelling guidelines GEOG 5060 GIS & Environment Lecture 4 • In order to ensure that model results are as close to reality as possible the following guidelines apply: – – ensure data quality beware of making too many assumptions match model complexity with process complexity compare predicted results with empirical data where possible and adjust model parameters and constants to improve goodness of fit – use results with care! Lecture 4 GEOG 5060 - GIS and Environment 17

Basics of cartographic modelling GEOG 5060 GIS & Environment Lecture 4 • Mathematics applied to raster maps – often referred to as map algebra or ‘mapematics’ – e. g. combination of maps by: • • addition subtraction multiplication division, etc. – operations on single or multiple layers Lecture 4 GEOG 5060 - GIS and Environment 18

A definition GEOG 5060 GIS & Environment Lecture 4 “A generic means of expressing and organising the methods by which spatial variables and spatial operations are selected and used to develop a GIS model” Lecture 4 GEOG 5060 - GIS and Environment 19

A simple example… 4 1 5 2 3 4 6 13 7 6 10 5 8 5 + Input 2 3 2 7 7 2 4 7 4 6 6 1 Lecture 4 3 1 Input 1 6 3 4 2 3 6 2 3 4 4 1 2 7 6 2 2 3 GEOG 5060 GIS & Environment Lecture 4 6 5 5 = Output 10 GEOG 5060 - GIS and Environment 20

Question… GEOG 5060 GIS & Environment Lecture 4 • How determine topological relationships? i. e. Boolean: AND, NOT, OR, XOR • What is the arithmetic equivalent? Lecture 4 GEOG 5060 - GIS and Environment 21

Building spatial models GEOG 5060 GIS & Environment Lecture 4 • It is (in theory) surprisingly simple: – algebraic combination of: • • • – interfaces • • Lecture 4 OPERATORS and FUNCTIONS rules and relationships inputs (and outputs) run at the command line/menu interface batch file embedded in system macro/script ‘hard’ programmed into system GEOG 5060 - GIS and Environment 22

Problems in model building GEOG 5060 GIS & Environment Lecture 4 • knowledge – systems and processes – relationships and rules • compatability – input data available – outputs required • quality issues – data quality (accuracy, appropriateness, etc. ) – model assumptions and generalisation – confidence and communication Lecture 4 GEOG 5060 - GIS and Environment 23

Modelling in Arc/Info GRID • Four basic categories of functions in map algebra: – – • GEOG 5060 GIS & Environment Lecture 4 local focal zonal global Operate on user specified input grid(s) to produce an output grid, the cell values in which are a function of a value or values in the input grid(s) Lecture 4 GEOG 5060 - GIS and Environment 24

Local functions GEOG 5060 GIS & Environment Lecture 4 • Output value of each cell is a function of the corresponding input value at each location – – – value NOT location determines result e. g. arithmetic operations and reclassification full list of local functions in GRID is enormous • • Lecture 4 Trigonometric, exponential and logarithmic Reclassification and selection Logical expressions in GRID Operands and logical operators Connectors Statistical Other local functions GEOG 5060 - GIS and Environment 25

Local functions 5 7 4 25 input 49 16 Lecture 4 GEOG 5060 GIS & Environment Lecture 4 output = sqr(input) GEOG 5060 - GIS and Environment 26

Some examples GEOG 5060 GIS & Environment Lecture 4 input output = tan(input) Lecture 4 output = reclass(input) GEOG 5060 - GIS and Environment output = log 2(input) 27

Focal functions GEOG 5060 GIS & Environment Lecture 4 • Output value of each cell location is a function of the value of the input cells in the specified neighbourhood of each location • Type of neighbourhood function – various types of neighbourhood: • – Lecture 4 3 x 3 cell or other calculate mean, SD, sum, range, max, min, etc. GEOG 5060 - GIS and Environment 28

Focal functions 5 7 4 GEOG 5060 GIS & Environment Lecture 4 input 11 16 Lecture 4 output = focalsum(input) GEOG 5060 - GIS and Environment 29

Some examples GEOG 5060 GIS & Environment Lecture 4 input output = focalmean(input, 20) Lecture 4 output = focalstd(input) output = focalvariety(input) GEOG 5060 - GIS and Environment 30

Neighbourhood filters GEOG 5060 GIS & Environment Lecture 4 • Type of focal function – used for processing of remotely sensed image data – change value of target cell based on values of a set of neighbouring pixels within the filter – size, shape and characteristics of filter? – filtering of raster data • • Lecture 4 supervised using established classes unsupervised based on values of other pixels within specified filter and using certain rules (diversity, frequency, average, minimum, maximum, etc. ) GEOG 5060 - GIS and Environment 31

Supervised classification 1 3 4 2 4 5 1 2 4 1 4 2 3 5 Old class Lecture 4 1 GEOG 5060 GIS & Environment Lecture 4 1 1 2 2 New class GEOG 5060 - GIS and Environment 32

Unsupervised classification GEOG 5060 GIS & Environment Lecture 4 5 diversity 1 3 4 2 4 5 1 2 4 4 modal 1 minimum 5 3 maximum mean Lecture 4 GEOG 5060 - GIS and Environment 33

Zonal functions GEOG 5060 GIS & Environment Lecture 4 • Output value at each location depends on the values of all the input cells in an input value grid that shares the same input value zone • Type of complex neighbourhood function – – Lecture 4 use complex neighbourhoods or zones calculate mean, SD, sum, range, max, min, etc. GEOG 5060 - GIS and Environment 34

Zonal functions 5 GEOG 5060 GIS & Environment Lecture 4 7 4 input Zone 2 zone Zone 1 9 7 9 9 Lecture 4 7 7 9 9 7 output = zonalsum(zone, input) 7 GEOG 5060 - GIS and Environment 35

Some examples input 535. 54 766. 62 Input_zone 127 6280 160 output = zonalthickness(input_zone) zonalmax(input_zone, input) Lecture 4 GEOG 5060 GIS & Environment Lecture 4 10800 output = zonalperimeter(input_zone) GEOG 5060 - GIS and Environment 36

Global functions GEOG 5060 GIS & Environment Lecture 4 • Output value of each location is potentially a function of all the cells in the input grid – – e. g. distance functions, surfaces, interpolation, etc. Again, full list of global functions in GRID is enormous • • • Lecture 4 euclidean distance functions weighted distance functions surface functions hydrologic and groundwater functions multivariate. GEOG 5060 - GIS and Environment 37

Global functions 5 7 input 4 6 7 5 4 4 Lecture 4 8 6 5 9 7 5 8 6 6 GEOG 5060 GIS & Environment Lecture 4 7 output = trend(input) 6 GEOG 5060 - GIS and Environment 38

Distance functions GEOG 5060 GIS & Environment Lecture 4 • Simple distance functions – – calculate the linear distance of a cell from a target cell(s) such as point, line or area use different distance decay functions • • – – Lecture 4 linear non-linear (curvilinear, stepped, exponential, root, etc. ) use target weighted functions use cost surfaces GEOG 5060 - GIS and Environment 39

Some examples input GEOG 5060 GIS & Environment Lecture 4 source output = eucdistance(source) output = eucdirection(source) output = costdistance(source, input) Lecture 4 GEOG 5060 - GIS and Environment 40

Lecture 4 COSTPATH example GEOG 5060 GIS & Environment Lecture 4 GEOG 5060 - GIS and Environment 41

Conclusions GEOG 5060 GIS & Environment Lecture 4 • Linking/building models to GIS • Idea of maths with maps – – surprisingly simple, flexible and powerful technique basis of all raster GIS • Fundamental to spatial interpolation, distance and neighbourhood functions Lecture 4 GEOG 5060 - GIS and Environment 42

Workshop GEOG 5060 GIS & Environment Lecture 4 • Constructing models in Arc/Info GRID – Demonstration of GRID functions • • • Lecture 4 Focal functions Local functions Global functions Zonal functions AML for GRID GEOG 5060 - GIS and Environment 43

Practical GEOG 5060 GIS & Environment Lecture 4 • Facilities location using Arc/Info GRID • Task: Locate suitable sites for a wind farm in the Yorkshire Wolds • Data: The following datasets are provided… – Digital elevation model (50 m resolution 1: 50, 000 OS Panorama data) – Contour data (10 m interval 1: 50, 000 OS Panorama data) – ITE land cover map (25 m resolution) – Roads (1: 250, 000 Meridian data) – Wind speed data Lecture 4 GEOG 5060 - GIS and Environment 44

Practical GEOG 5060 GIS & Environment Lecture 4 • Steps: 1. Formulate a location model based on available data and requirements for a wind farm 2. Pre-process data to create model input layers as required 3. Run model 4. Identify best location(s) Lecture 4 GEOG 5060 - GIS and Environment 45

Lecture 4 Siting wind turbines GEOG 5060 GIS & Environment Lecture 4 GEOG 5060 - GIS and Environment 46

Practical GEOG 5060 GIS & Environment Lecture 4 • Experience at simple cartographic model building • Experience with spatial modelling functions within Arc/Info GRID • Familiarity with locational models and wind farm siting in particular Lecture 4 GEOG 5060 - GIS and Environment 47

Next week… GEOG 5060 GIS & Environment Lecture 4 • Terrain modelling 1: the basics – DEMs and DTMs – Derived variables – Example applications • Workshop: Terrain modelling in Arc/Info and Grid • Practical: Using DEMs Lecture 4 GEOG 5060 - GIS and Environment 48