programming in arcgis ii - lunds...

David Tenenbaum – NGEN13 – Lund University

Programming in ArcGIS II

• In ArcGIS, tools not only appear in the middle of

processes in ModelBuilder, but they can also be

represented by equivalent Python code

• In fact, whether you are using a tool straight from

ArcToolbox, or are adding a tool to a model in

ModelBuilder, what you are really doing in both of

those cases is making use of a graphical user

interface that creates an appropriate line of Python

code for ArcGIS to run

• Python code is the fundamental way that ArcGIS’

geoprocessing functions work in recent versions


Programming in ArcGIS II

• The equivalency of GUI tool to a process in

ModelBuilder to a line of Python code, and the fact that

we can drag and drop items between these parts of

ArcGIS, makes it pretty easy to learn how to use them:

– We can work out details of how to use a tool in its GUI

– We can then drag and drop that into ModelBuilder and

combine it with other tools

– We can drag and drop to the Python command line (or

request the Python code for a complete model) and then we

can see how it looks as code

• This way, we can learn Python code incrementally, by

using the GUI to help us


Object-oriented Programming

• Object-oriented programming (OOP) is a programming

approach that uses "objects" to design applications and

computer programs

– This is contrast to modular or procedural programming that

you might be familiar with, where lines of code are numbered

and run in sequence

• Even though it originated in the 1960s, OOP was not

commonly used in mainstream software application

development until the 1990s

• Today, many popular programming languages (such as

Java, JavaScript, C#, VB, .Net, C++, Python, PHP, Ruby

and Objective-C) support OOP



Important OOP terminology:

• Object - Anything that can be ‘seen’ or ‘touched’ in the

software programming environment . Objects have a

value, a type, and methods

• Value – The value is what the object contains:

– e.g. >>> name = “Paul”

• Type – The type defines the kind of object:

– e.g. >>> type(name) returns

• Methods - An object’s methods are operations that the

object can perform or that can be performed upon the

object



Important OOP terminology:

• Class - A pattern or blueprint for creating an object. It

contains all the properties and methods that describe the

object

• Instance - The object you create from a class is called an

instance of a class

• Distinguishing an object/instance vs. a class, examples:

– Cookie vs. a cookie-cutter

– Car vs. the blueprint for manufacturing the car


ArcObjects

• So where do ArcObjects come into the picture?


• ArcObjects are platform

independent software

components, written in C++,

that provide services to support

GIS applications

• Because this architecture

supports a number of unique

ArcGIS products with

specialized requirements, all

ArcObjects are designed and

built to support a multi-use

scenario

ArcObjects


ArcObjects

• You can think of ArcObjects as the stuff that the insides

of ArcGIS is made of … all the structure and

functionality that allows ArcGIS to do what it does

• ArcObjects are a set of computer objects specifically

designed for programming ArcGIS applications, and

they include things that have manifestations you can see

onscreen, as well as more abstract data objects

• Anytime you have used ArcGIS, whether or not you knew

it, you have been using ArcObjects … but what we will

learn is how to work with them in more powerful ways

than just through the user interface


Object Model Diagrams

• Part of the process of learning how to program any

object-oriented language is to learn about the classes

available in that language and their relationships. This

includes:

– Learning what properties and methods a class has

– Learning the relationships between classes so you understand

how one gets from one class to another

• There is no substitute for experience (i.e. actually

writing Python code and using the classes, setting and

getting their properties, using their methods) … but object

model diagrams (OMDs) are a useful guide to the set of

classes in a particular language / package


Object Model Diagram for ArcPy in ArcGIS 10.0


• Let’s zoom in a little and have a look:

• The light blue box on the left is the arcpy

object itself

• Properties are listed at the top

• Below those, methods are listed

• The symbols to the left of the properties

and methods tell you a little about them,

using a symbology called the Unified

Modeling Language

• Here’s the key for this from the OMD:

OMD for ArcPy in ArcGIS 10.0 - arcpy


Unified Modeling Language Diagrams - Classes

• Part of what a Unified Modeling Language (UML)

diagram shows you is the characteristics of a class:

Parcel

Value: Currency

Zoning: String

Calculate Tax (): Currency

Class Name

Properties

Methods

• While these diagrams are useful to us just to see the

characteristics of a class, their real power comes in

showing us the relationships between the classes in the

object model


BirdAbstract

ChickenCoClass

NestClass

*

WingsClass

2

FarmCoClass

EggClass

• Is a type of

• Is composed of

• Creates a(n)

• Multiplicity

• Association

Unified Modeling Language Diagrams –

Relationships Between Classes

• Unfortunately, we

do not have a full,

proper UML

diagram of ArcPy


Object Model Diagram for ArcPy in ArcGIS 10.1


Object Model Diagram for ArcPy in ArcGIS 10.2.1

Here are arcpy

classes and

functions



– arcpy Classes and Functions

• Still too small to read!

• I will provide the PDFs

Here is the FieldInfo class



– FieldInfo Class

• Unfortunately, this is not a

proper UML class diagram

• No ‘barbells’ to show if one

can put a property …

• It still lists methods and

properties

• It still identifies types for

properties, and parameters

and types of objects

returned for methods

It is still extremely useful for learning the object model!



arcpy

classes &

functions

Geometry

& Spatial

Classes

Data Access Module

Time ModuleGraph

Generation

Network Analyst

Module

Geospatial

Analyst Module

Mapping

Module

Spatial

Analyst

Module



– Mapping Module

• Also too small to read!

• You will use the PDF


ArcPy – Mapping Module

• The Mapping Module allows you to manipulate maps

using code, in terms of both their content and appearance

– This includes both the kinds of tasks you would perform in the

Data View or the Layout View of ArcMap

• This includes dealing with map documents:

– Saving, printing, and exporting map documents

• It includes managing data frames:

– Adding and removing layers, updating the frame

• It also includes manipulating the appearance of layers:

– Changing or controlling all aspects of their appearance

• Finally, it can control all aspects of layout elements:

– Position and values of all elements


ArcPy – Mapping Module

Map Element

Map Document Data Frames Layers Layout Elements

Operations

Save Add, Remove

Layers

Change Names Modify Text,

Legend, Map

Surround,

Picture, and

Graphical

Elements

Page Position

and Values

Print

ExportChange Frame

Size, Rotation,

Scale, Units,

Spatial

Reference, etc.

Get/Set Extent

Zoom to Selected

Change Visibility

Change

Transparency

Labels On/Off

Apply Definition

Queries

Modify Groups


Querying and Selecting Using Python Code

• Querying is one of the easier things to learn how to

do in Python code if already know how to use queries

in ArcGIS

• It fits into the original Geoprocessing framework

that Python was designed to control in ArcGIS

• There are arcpy methods for both

– Select by Location – arcpy.SelectLayerByAttribute_management

– Select by Attributes – arcpy.SelectLayerByLocation_management

• The functionality mirrors that of the tool interfaces,

and the tool interfaces can even export Python code

to help you learn how to code it yourself …

programming in arcgis ii - lunds...

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