if row1.parcelid == row2.parcelid: print row.shape.area

Transcription

1 ArcGIS Geoprocessing Geoprocessing:: Python Scripting - Advanced Techniques Nathan Warmerdam

2 Workshop Outline The Geoprocessor in scripting Cursors Reading and writing geometry Creating and using objects for parameter values Effective error handling Working with ArcGIS Server geoprocessing services Submitting jobs and getting results Additions of note in 9.3 2

3 The geoprocessor Pythonic import arcgisscripting gp = arcgisscripting.create( arcgisscripting.create( )) CrossCrossPlatform Supported Versions 9.3 import arcgisscripting gp = arcgisscripting.create() arcgisscripting.create() 9.2, 9.3 iimportt win32com.client i 32 li t gp = win32com.client.dispatch( esri win32com.client.dispatch( esri , 9.1, 1 9.2, htt // bh l i / i d kt /9 3/i d f?id 842& id 839&topicname=Differences_between_geoprocessor_versions The Th dispatch di t h object bj t may be b used d in i a variety i t off other th scripting i ti languages (Perl, VBScript, JScript) JScript) 3

4 The geoprocessor Advantages of using a 9.3 geoprocessor 1 Boolean 1. B l properties i are true Booleans B l (not ( strings i or a 0 / 1) 1) 2. List functions return Python lists (not enumerations enumerations)) 3 All tools 3. t l return t a result lt object bj t 4. Extent and point properties are returned as extent and point objects (not delimited strings) 5 Returns 5. R t U Unicode i d instead i t d off strings ti (supports ( t non non-ascii characters) 4

5 Accessing Data with Cursors Cursors allow record by record access of field values Moving values from one table or feature class to another if row1.parcelid == row2.parcelid: row1.owner 1 = row2.owner 2 Accessing properties of a feature s geometry print row.shape.area 5

6 Available Cursors Search Cursor - data access (read only) Update Cursor - data modification (read, write) Insert Cursor Cursor-- data addition (write only) 6

7 Accessing Data with a Search Cursor SearchCursor (PathToData PathToData,, WhereClause, WhereClause, SpatialReference,, FieldList SpatialReference FieldList,, SortFields): SortFields): SC Object From the Search Cursor object you get a Row Fields Fi ld are accessed d as properties ti off the th row object bj t Use the row object s GetValue method if your field name is a variable When done, delete row and cursor objects to remove data locks Use options to limit the records For example, the where clause is the same as using a definition query on a layer 7

8 Accessing Data with a Search Cursor import arcgisscripting gp = arcgisscripting.create(9.3) typefield = gp.getparameterastext(0) gp ( / / y g / ) sc = gp.searchcursor( D:/data/reedley.gdb/roads ) row = sc.next() # Print road name and road type while hil row: if row.getvalue(typefield) == hwy : print Modifying HWY: + row.name # do stuff row = sc.next() del row del sc 8

9 Reading Feature Geometry 9

10 Reading Feature Geometry Knowing the hierarchy of geometry is important A feature class is made of features A feature is made of parts A part is made of points In Python terms A single part feature looks like this [ [pnt [pnt,, pnt, pnt, pnt] pnt] ] A multipart polygon feature looks like this [ [pnt [pnt,, pnt, pnt, pnt],[ pnt],[pnt pnt,, pnt, pnt, pnt] pnt] ] A single part polygon feature with a hole (inner ring) looks like [ [pnt [pnt,, pnt, pnt, pnt, pnt,,pnt pnt,, pnt, pnt, pnt] pnt] ] 10

11 Reading Feature Geometry Use the PartCount property to get the number of parts for a feature Use the GetPart method to retrieve the desired part A null point is used as a separator between rings (holes) in a polygon part # Reading g lines x = 0 while x < feat.partcount: roadarray = feat.getpart(x) pnt = roadarray.next() while pnt: print pnt.x, pnt.y pnt t = R RoadArray.Next() da N t() x = x

12 Reading Feature Geometry Need coordinate information in a different coordinate system? Features may be projected onon-the the--fly using the Spatial Reference parameter # C Create eate a S SR object from o a p projection oject o file e SR = gp.createobject( spatialreference ) SR.CreateFromFile( c:/nad 1983 UTM Zone 10N.prj ) # Create search cursor, using GCS spatial reference rows = gp.searchcursor("d:/data.gdb/roads","", SR) row = rows.next() 12

13 Writing Feature Geometry To create new features use an Insert cursor rows = gp gp.insertcursor("d:/data.gdb/roads ) ( / g / ) row = rows.newrow() An Update cursor can be used to replace existing geometry Use the Point and Array objects to create feature parts A part may be used to set a geometry field A multipart feature is an array containing other arrays, where each array is a part 13

14 Writing Feature Geometry # Open an insert cursor for the feature class cur = gp.insertcursor( D:/data.gdb/roads ) # C Create t array and d point i t objects bj t linearray = gp.createobject("array") pnt = gp.createobject("point") # Add two points to the array pnt.x, pnt.y = , linearray.add(pnt) pnt.x, pnt.y = , linearray.add(pnt) # Create a new row, or feature, in the feature class feat = cur.newrow() # Set the geometry of the new feature to the array of points feat.shape = linearray # Insert the feature cur.insertrow(feat) 14

15 Writing Feature Geometry The validity y of the g geometry y is checked before it is added Problems such as invalid ring order are corrected automatically Uses the same process used by the Repair Geometry tool Writing g features requires a schema lock on the data Use the TestSchemaLock method to check 15

16 Tools and Parameters A geoprocessing tool has a collection of parameter t values l Parameters tell the tool what to do 16

17 Using Objects to Set Parameters Most tool parameters are easy to define with a string or a number Such as a data path or buffer distance Other Oth parameters t are nott easy to t define d fi with ith a string ti Such as a spatial reference or field mapping Geoprocessing objects can be used to set these parameters Many ways to create geoprocessing objects The CreateObject method The Describe object, has properties that return Objects 17

18 Using Objects to Set Parameters Use the SpatialReference object as a parameter value import arcgisscripting gp = arcgisscripting.create(9.3) arcgisscripting create(9 3) # Describe a dataset with a specific Spatial Reference desc = gp.describe gp.describe("d:/data/reedley.gdb/city gp.describe( ( ("D:/data/reedley.gdb/city D:/data/reedley.gdb/city_boundary boundary") ) # Create the FDS using the describe object's SR Object gp.createfeaturedataset("d:/data/ gp.createfeaturedataset gp ("D:/data/reedley.gdb,"NewFDS ( reedley.gdb,"newfds", y g, ",, desc.spatialreference) desc.spatialreference ) 18

19 Using Objects to Set Parameters Some parameters accept multiple values (Multivalue (Multivalue)) Multivalue parameters may be expressed in two ways: As a string ("value1;value2;value3") As a Value Table Use LoadFromString method to load a multivalue string Use U ExportToString E tt St i to t create t an output argument value Useful for script tools 19

20 Using Objects to Set Parameters Overlay tools, such as Union use Value Tables with multiple columns Difficult to parse multivalue string when more than one column is used import arcgisscripting gp = arcgisscripting.create(9.3) # Create a value table with 2 columns vt = gp.createobject('valuetable', 2) # Add 3 feature classes with ranks to the value table vt addrow("c:/base/counties vt.addrow( c:/base/counties.shp shp 1") 1 ) vt.addrow("c:/base/parcels.shp 1") vt.addrow("'c:/base/state boundary.shp' 2") # Run Union using the value table as input gp.union(vt, "c:/output/landinfo.shp") 20

21 Error Handling Syntax errors Detected when compiled Execution errors Add error handling routines to catch errors Tool error messages can be retrieved from the geoprocessor Errors you raise (or assert) yourself Use Raise and Assert statements to trigger specific exceptions Especially useful when using tools and native methods together Provides more meaningful g context for messages g 21

22 Error Handling import arcgisscripting gp = arcgisscripting.create(9.3) # Get input and output feature classes fc = gp.getparameterastext(0) outfc = gp.getparameterastext(1) try: # If the input has point feature raise an error if gp.describe(fc).shapetype == "Point": raise Exception, "Feature Class should not be point" else: gp.featuretopoint(fc, outfc) # Geoprocessing Errors will be caught here except arcgisscripting.executeerror: print gp.getmessages(2) # Other errors will get caught here except Exception, ErrorDesc: print ErrorDesc.message 22

23 Error Handling Use the traceback module to get Python errors except: import traceback, sys # get t th the traceback t b k object bj t tb = sys.exc_info()[2] # tbinfo contains the failure s line number and the line s code tbi f = traceback.format_tb(tb)[0] tbinfo t b k f t tb(tb)[0] print tbinfo # provides where the error occurred print sys.exc_type # provides the type of error print i t sys.exc_value l # provides id th the error message 23

24 Demo Cursors, Complex Objects and Error Handling 24

25 What is a Geoprocessing Service? Geoprocessing functionality published to ArcGIS Server Se e Tasks in a service can be any script or model tool created in ArcGIS Desktop Geoprocessing services can be used by several clients Desktop, Engine, Explorer, Server web clients, Python Scripting Geoprocessing services have two modes of execution Asynchronous Your code must ping server for status Synchronous Your code waits for server to finish 25

26 Accessing Geoprocessing Services A geoprocessing service can be thought of as a remote toolbox Can be added to your script with the AddToolbox method Tasks availabe from the service are then used like normal tools gp.addtoolbox(" gp.addtoolbox (" Service URL Folder GP Service gp.addtoolbox( gp AddToolbox( flame7;gp/ gp.addtoolbox AddToolbox( flame7;gp/surfacemodels ( flame7;gp/surfacemodels flame7;gp/surfacemodels SurfaceModels") ") ) Local Host Name 26

27 Working with Geoprocessing Services Input p to a g geoprocessing p g service can be: Record set Feature set Raster dataset String, Double, Long, Date, File, Linear Unit, Boolean Feature sets and record sets Can be created as objects via our scripting module Lightweight representations of feature classes and tables To use as input, input create an empty object object, and load data in 27

28 Working with Geoprocessing Services When a server tool is executed it returns a result object The result object j is how you y interact with the server The GetOutput method retrieves data from the server The GetMapImageURL method retrieves an output s map service as an image 28

29 Demo Geoprocessing Services 29

30 Accessing a Result s Output import arcgisscripting import time gp = arcgisscripting.create(9.3) gp.addtoolbox(" infeatset = gp.createobject("featureset") infeatset.load("c:/base/towers.shp") results = gp.bufferpoints(infeatset, "5 feet") # Service is asynchronous. Wait until the job has completed while results.status < 4: time.sleep(0.2) # Get an output Feature Set back and save locally outfeatset = result.getoutput(0) gp.copyfeatures(outfeatset,"c:/temp/base.gdb/towers gp.copy eatu es(out eatset, C:/te p/base.gdb/to e s_bu buffer") e ) 30

31 Additions of note at

32 AddFieldDelimiters Method The syntax used to build an SQL expression varies on the data source The AddFieldDelimiters method removes the guess work in getting the appropriate field delimiters in your SQL expression crimefc = c:/data/crime c:/data/crime.mdb/crime mdb/crime # Use AddFieldDelimiters to add correct delimiters dfield = gp gp.addfielddelimiters(crimefc, (, BEAT ) ) query = dfield + = 1 gp.select(crimefc, c:/data/crime.mdb/beat1, query) 32

33 Using geometry directly in Geoprocessing Tools In 9.3 you can use geometry from the row directly in a geoproceeing tool. tool import arcgisscripting, os gp = arcgisscripting.create() arcgisscripting create() fc = "F:/data/USCounties.shp" sc = gp.searchcursor(fc) row = sc.next() while row: name = row.name + "_" + row.state feat = row.shape # use the geometry directly in copy features gp.copyfeatures(feat, "F:/data/counties.gdb/%s" % name) row = sc.next() 33

34 ArcSDESQLExecute Object For users that are experienced using SQL against ArcSDE geodatabases and would like a more i t integrated t d approach h to t sending di their th i SQL to t the th ArcSDE database Supports most SQL statements DML eg eg.. SELECT, INSERT, UPDATE, UPDATE DELETE DDL eg eg.. CREATE, DROP, ALTER SQL functions with ST_GEOMETRY spatial type for Oracle, DB2, Informix and PostgreSQL Oracle Spatial functions against SDO_GEOMETRY spatial type 34

35 ArcSDESQLExecute Object Very important to understand the impact of issuing SQL Statements against Geodatabase objects. Please read the ArcGIS Working with geodatabases using SQL book for guidance. 35

36 Help Resources Scripting / Tool documentation Geoprocessing G Resource Center C Python References Learning Python by Mark Lutz Core C P Python th b Wesley by W l J. J Chun Ch Dive Into Python by Mark Pilgrim Python Organization 36

37 Thank you y please don t forget to fill out an evaluation form! 37