ArcObjects_Pyton

www.geonorth.comValue Through Integration and Innovation

GIS and Engineering

• Mark Pearson, PE (civil)

• GeoNorth, LLC– GIS, Database, Internet Consulting– Anchorage, Portland– 13 Years Old (91 DOGS Years)– App Development, Planning, Conversion– Huge to Tiny Projects/Organizations


The Plan

• ArcObjects– Concepts– Examples

• Python– Concepts– Examples

• Compare/Contrast

• Discussion


Multiple Ways to Skin the Cat


ArcObjects: Serious Programming

• AML– Throw commands into text file and you’re a

programmer

• Avenue– Proprietary Language


ArcObjects

• Not a Language• Building Blocks Upon

which ArcGIS was built• COM objects • Most commonly used

with VisualBasic or C++


ArcObjects: First Rule

Whining


VisualBasic


Modeling the Real World

• Objects


Object Oriented

Map Car

Property MapUnits Horsepower

Method AddLayer Accelerate

Event SelectionChanged Brakes are pressed


Object Orientation

• Properties– Characteristics (nouns)

• Methods– Actions object knows how to perform (verbs)

• Events– Occurrences that Object can respond to


Objects Vs. Classes


Objects Vs. Classes

• Class is the “Blueprint”

• Object is the “House”– An instantiation


Interface vs. Objects


Interfaces vs. Objects

Dim pFeatureLayer As IFeatureLayerDim pAttributeTable as IAttributeTableSet pFeatureLayer = new FeatureLayerSet pAttributeTable = pFeatureLayer ‘Query Interface


Tips

• Learn all of the on-line resources and use them

arcobjectsonline.esri.com


Tips

• Use Samples– Lots of Them– Almost Never Start from Scratch


Tips

• Training is Worth It for quick jump start

• We have an ArcObjects course in March (hint)


Tips

• Spend Time on Error Handling


ArcObjects

• For hard-core programmers = Nirvana

• For casual programmers = Purgatory

• Non programmers = Hell


ArcObjects: Before & After

Before ArcObjects After ArcObjects


ArcObjects

• Up Side: Granularity of Control

• Down Side: Nothing is Easy*

* For the casual user


Common Implementations

• Quick & Dirty Automation using VBA within ArcMap

• Separate stand-alone applications

• ‘Extensions’ to ArcGIS framework– Compiled DLL(s)


Example in ArcObjects

• Example: Programmatically Turn a Layer Off


Private Sub TurnOffLayer() Dim pDoc As IMxDocument Dim pMap As IMap Dim pLayer As ILayer Dim pActiveView As IActiveView

Set pDoc = ThisDocument Set pMap = pDoc.FocusMap Set pLayer =


Private Function FindLayerByName(strLayerName As String, pMap As IMap) As ILayer Dim i As Integer For i = 0 To pMap.LayerCount - 1 If UCase(pMap.Layer(i).Name) = UCase(strLayerName) Then Set FindLayerByName = pMap.Layer(i) Exit Function End If Next i Set FindLayerByName = Null

End Function


Private Sub TurnOffLayer() Dim pDoc As IMxDocument Dim pMap As IMap Dim pLayer As ILayer Dim pActiveView As IActiveView

Set pDoc = ThisDocument Set pMap = pDoc.FocusMap Set pLayer = FindLayerByName("parcels", pMap) pLayer.Visible = False

End Sub

Set pActiveView = pMap ‘this is a query interface pActiveView.Refresh pActiveView.ContentsChanged


ArcObjects 8.x to 9.0

• Good News: not much pain

• Binary Compatibility for most core-level libraries

• Not like Avenue versus ArcObjects


Type Libraries: Diced Up

• Esricore.olb was one huge library

• Now slit into functional groups


Type Libraries: Diced Up

Declarations

Dim pEnv as esriCore.IEnvelope Dim pEnv as esriGeometry.IEnvelope

ZoomToPoint (inPt as esricore.IPoint) ZoomToPoint(inPt As esriGeometry.IPoint)

Instantiations

Set pPt = new esriCore.Point set pPt = New esriGeometry.Point

Implementations

Implements esricore.ITool Implements esriFramework.ITool

ArcObjects 8.x ArcObjects 9.0


ArcGIS 9.0 Type LibrariesArcGIS Engine UI •esriSystemUI•esriDisplayUI•esriOutputUI•esriGeoDatabaseUI•esriDataSourcesRasterUI•esriLocationUI•esriCartoUI •esriCadUI•esriIMSUI •esriTinUI•esriCatalogUI ArcGIS Application assemblies•esriArcMapUI•esriArcMap•esriArcCatalogUI•esriArcCatalog•esriEditor•esriEditorExt•esriGeoDatabaseDistributedUI•esriGeoReferenceUI

ArcGIS EngineesriSystemesriGeometryesriDisplayesriOutputesriGeoDatabaseesriDataSourcesFileesriDataSourcesGDBesriDataSourcesOleDBesriDataSourcesRasteresriGeoDatabaseDistributedesriLocationesriCarto esriCadesriIMS esriTinesriWorker esriFramework


Code Converter Utility

• VB6 Add-In• Removes ESRI Object Library from Project

reference• Replaces ‘esriCore.’ with appropriate name in:

• Declarations• Instantiations• Implementations• ProgIDs

• Adds appropriate new references according code that is found


Tips for Healthy ArcObjects Use

• Never over promise amount of time

• Always plagiarize Code• ArcObjects Online / Samples• Knowledgebase• Your own code

• Keep a ‘Toolbox’ of common routines

• Make subs/functions generic whenever you can


•Python/Scripting


Scripting in ArcGIS

• Python

• VBScript

• Perl

• Jscript

• Any scripting language that is COM compliant

• Python is ESRI-prefered


Why Python?

• Easy to learn, clean, clear syntax

• Supports Object Oriented programming

• Works well with complicated data structures

• Simple to integrate with C++ and Fortram

• Can be seamlessly integrated with Java

• Free, Open Source, Widely Used


Python

• Not invented by ESRI

• Interpreted, interactive, object-oriented

• Invented in 1991 by Guido von Rossum, Netherlands

• Named after Monty Python

• www.python.org

• Platforms: Windows, all UNIX, OS/2, Mac, Amiga – even Nokia cell phones


Geoprocessing with Python

• Geoprocessor Programming Model


Scripts in ArcToolBox


Importing Modules

• Python scripts are Modules• Use the ‘import’ statement to load and use

modules• All geoprocessing scripts use the ‘win32com’

module– Supports communciation between Python and

the COM IDispatch interface, which is used by the geoprocessor

• Other modules to math, file I/O, OS stuff, etc.


Standard Stuff at in a Python Script

import win32com.client, sys, os– sys is python system, user input, etc.

– Os does OS-specific file manipulation

#Create the Geoprocessor object

GP = win32com.client.Dispatch("esriGeoprocessing.GpDispatch.1")– Declares and creates geoprocessing object that you will use later

#Set the input workspace

GP.workspace = “c:\data\anchorage\shapes”

GP.workspace = sys.argv[1]


Indentation and Spaces

• They are relevant!

try:

#get a list of featureclasses in workspace

fcs = GP.ListFeatureClasses()

Python is also case sensitive !!!

gp is not the same as GP


Batch Processing

• ListDatasets (Wild Card, Dataset Type)• ListFeatureClasses (Wild Card, Feature Type)• ListFields (Input Value, Wild Card, Field Type)• ListIndexes (Input Value, Wild Card)• ListRasters (Wild Card, Raster Type)• ListTables (Wild Card, Table Type)• ListWorkspaces (Wild Card, Workspace Type)

• All return an Enumeration (list with unknown count)


Batch Example

# Import COM Dispatch module

from win32com.client import Dispatch

# Create the geoprocessor object

GP = Dispatch("esriGeoprocessing.GPDispatch.1")

# Set the workspace. List all of the feature classes that start with 'G'

GP.Workspace = “c:/data/anchorage/anch.mdb”

fcs = GP.ListFeatureClasses("G*")

# or for a type: fcs = GP.ListFeatureClasses("G*","polygon")


Batch Example

# Reset the enumeration to make sure the first object is returnedfcs.reset()# Get the first feature class namefc = fcs.next()while fc: # While the feature class name is not None # Copy the features from the workspace to a folder GP.Copy(fc,“c:\data\anchorage\dataout\” + fc) # Get the next feature class name fc = fcs.next()


Licensing

• When a tool is executed, either thru the ArcToolbox or thru Script, an ArcGIS Desktop license is required

• Extension Licenses, too


Extending Python with Wrappers

• Vector Formats– pyshapelib (shapelib.maptools.org)

• Access to individual vertices of the shape• Dbf file• Indexing

– OGR (gdal.maptools.org/ogr)• Other vector formats like MapInfo, Coverage,

PostGIS, Oracle Spatial, TIGER, SDTS, OpeNDAP, DGN, Microstation DGN



• Grids– Geodata Abstration Library GDAL

(gdal.maptools.org)• JPEG2000, BSP, USGS DEM, Military• Elevation Data, ECW, GRASS, TIFF/GeoTIFF,

NetCDF, Imagine, and SDTS



• Projections– pyProjection

(http://hobu.biz/index_html/software/pyprojection)• For projecting coordinates from one to another• Uses EPSG code system and/or you can roll your own

• SDE– PySDE (hobu.stat.aistate.edu/pysde)

• Wrapper for SDE C API and has corresponding Python methods


ArcObjects or Python?

• Rearrange the ArcGIS User Interface?

• Batch project a bunch of feature classes?

• Create new tool to edit special Widget feature classes?

• Create an ‘Extension’ for ArcGIS?

• Automated Map Book Generation


Thanks

ArcObjects_Pyton

Documents

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