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Introduction to GIS Introduction to GIS Programming Programming
By Jun LiangBy Jun Liang
Department of GeographyDepartment of Geography
UNC-CHUNC-CH
AudiencesAudiences
Who might be interested in this topic?Who might be interested in this topic?
- Bored with repeating GIS operationsBored with repeating GIS operations
- Do not like the default look (GUI) of Do not like the default look (GUI) of Commercial softwareCommercial software
- Has difficulties in standardizing map outputHas difficulties in standardizing map output
- Functions you need are not available in your Functions you need are not available in your GIS softwareGIS software
Preparing for GIS ProgrammingPreparing for GIS Programming
- GIS software operations: know what are you doing
- Spatial Data Models:
Understand what are dealing with
- Basic Spatial Analytical Functions: Have a GIS brain
- Knowledge on Programming: Integer? Binary? Loops? Logical operators?
Can I do it?Can I do it?
Question Question –– can I write programs for GIS can I write programs for GIS applications? Is it difficult to do?applications? Is it difficult to do?
Answer Answer –– It depends on what do you want to It depends on what do you want to do. do.
At most time, you can, At most time, you can, at least I believe. at least I believe. It is just another language It is just another language –– easier than most foreign easier than most foreign languages.languages.
Where to start?Where to start?
It may already exist somewhere.It may already exist somewhere.
If you are looking a tool, a function,If you are looking a tool, a function,
wwhich you could not find in your GIS software, hich you could not find in your GIS software, you may google it first, or try to find it in a you may google it first, or try to find it in a community website, such as community website, such as arcscripts.esri.com.arcscripts.esri.com.
Write your own.Write your own.
GIS Interests are GrowingGIS Interests are Growing
Mapping/GeoVisualization
Spatial Information Management
Spatial AnalysisSpatial Modeling
GovernmentEducation/Research Business/Industry
Application ExamplesApplication Examples
- Public HealthPublic Health- Environmental StudiesEnvironmental Studies- Urban PlanningUrban Planning- Water Resources ManagementWater Resources Management- Crime Mapping / Crime Pattern AnalysisCrime Mapping / Crime Pattern Analysis- Store Location OptimizationStore Location Optimization- Internet Mapping / RoutingInternet Mapping / Routing- Transportation/LogisticsTransportation/Logistics
Complexity of GIS ApplicationsComplexity of GIS Applications
Simple
Complex
Data manage, Mapping
Query, Measurement
Basic spatial analysis
Advanced spatial analysis
Integrated expert systems
GIS programming could be used for different level applications.
Data VolumeData Volume
Before proceed to write programs for your GIS Before proceed to write programs for your GIS applications, you may already have finished applications, you may already have finished data collection. The size of your data data collection. The size of your data collection will affect the way you are going to collection will affect the way you are going to code.code.
- Large volume: multiple Gig bitesLarge volume: multiple Gig bites
- Intermediate volume: 100Mb – 1 GigIntermediate volume: 100Mb – 1 Gig
- Small volume: ~100MbSmall volume: ~100Mb
Geo-ComputationGeo-Computation
Complexity/CPUComplexity/CPU time is another factor you time is another factor you need to estimate, before you design your need to estimate, before you design your program.program.
- Several days +Several days +- Within a dayWithin a day - Several hours- Several hours
- Within an hour- Within an hour Issues you may need to Issues you may need to
decide: decide: hardware andhardware and algorithm algorithm
Data Flow – Program Flow ChartData Flow – Program Flow ChartCensusTracts
(Input Features) Clip (Analysis Tools/Proximity Toolset)
CensusTractsClip (in
TransformScratch.mdb)StreamBuffer(Clip Features)
The flow chart will explain:
Spatial functions/tools you need to use
Parameters for functions
Output definitions
Program Logic Structure/Work flow
Implementation StructuresImplementation Structures
There are different ways youThere are different ways youcan implement your GIScan implement your GISprograms, based on:programs, based on:- GIS software you usedGIS software you used- Availability of tools/functionsAvailability of tools/functions- The nature of your application (share with The nature of your application (share with
other people? Going to used by other other people? Going to used by other people who have limited GIS experiences? people who have limited GIS experiences? Etc.)Etc.)
First Approach – Write your own code First Approach – Write your own code without help from existing GIS softwarewithout help from existing GIS software
Your Research Project/Application/Model
GIS functions – neededby your model
Do not need spatial visualization; data management; hard to be shared or reused by other people; one time application.
Programming Programming –– on your own on your own
Some examples of the first approaches Some examples of the first approaches ––
(1)(1) Downloading data routinely from a website Downloading data routinely from a website and use them for your model.and use them for your model.
(2)(2) Analyzing the average transportation cost Analyzing the average transportation cost from one point to a set of points. (location from one point to a set of points. (location optimization.)optimization.)
You can use any programming languages you You can use any programming languages you are familare familiiar with, such as Java, C, etc.ar with, such as Java, C, etc.
Approach 2 – Customizing existing Approach 2 – Customizing existing GIS softwareGIS software
- Using macro - Using macro language to language to customize customize existing GIS existing GIS software: GUI software: GUI focused focused application. application.
Providing service Providing service to general to general public.public.
Approach 3 – Creating new functions Approach 3 – Creating new functions using GIS macro/scriptsusing GIS macro/scripts
GIS Software
Your GIS ProgramCoding spatial models, or other non-spatial models with GIS macro languages, scripts.
Approach 4 – Loosely and tightly Approach 4 – Loosely and tightly coupled integration coupled integration
GIS Software – Provides basic commands,
macros, etc.
External ProgramModule
Loosely-Couple Architecture for integrating your Models (scripts, codes, etc) with GIS software
Data
Tightly Coupled ApplicationsTightly Coupled Applications
GIS Software – Provides basic commands,
macros, etc.
Pre-compiled Programs
Data
GIS software can talk to some pre-compiled programs during execution – the integration usually looks seamless.
It is just like that you can edit Excel object in your Word document.
ArcGIS ProgrammingArcGIS Programming The most recent release of ESRI’s ArcGIS®
suite incorporates both Visual Basic and Python scripts. However, Python is well-suited to geoprocessing and much of the code in ArcGIS 9 that performs these types of functions is written in Python.
GUI-Interface Geo-processing
Changing A Layer’s NameChanging A Layer’s Name
MxDocument
Map
*
Layer
*
Application
FeatureLayer
RasterLayerr
LineElement
ElementGeometry
Color Symbol GraphicElement FrameElement
TextElement MarkerElement PolygonElement
To make graphics on a map, you create objects out of the coclass under GraphicElement.
Using Python for GeoprocessingUsing Python for GeoprocessingESRI chose Python as the support language for geoprocessing because:• Python is easy to learn because of its clean syntax and simple, clear concepts.• Python supports object-oriented programming in an easy-to-understand manner.• Documenting Python is easier because it has readable code.• Complicated data structures are easy to work with in Python.• Python is simple to integrate with C++ and Fortran.• Python can be seamlessly integrated with Java.• Python is free from the Web and has a widespread community.
An simple python exampleAn simple python example
import arcgisscripting gp = arcgisscripting.create() gp .Workspace = “c :\\Data\\Canada .mdb” gp.Buffer(”Streams”, “NoBuildZone”, 100) gp.Erase(”LandUse”, “NoBuildone”,
“BuildZone”)