17723238
Description
Quiz by Maggie Samson, updated more than 1 year ago
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Created by Maggie Samson
about 5 years ago
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Question 1
Question
Which cursors of the arcpy.da module can be used to work with geometry objects using SHAPE@?
Answer
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SearchCursor, UpdateCursor, and InsertCursor
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InsertCursor only
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SearchCursor only
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UpdateCursor only
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UpdateCursor and InsertCursor
Question 2
Question
Which of the following is not a geometry token in ArcPy?
Answer
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SHAPE@
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SHAPE@CENTROID
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SHAPE@XY
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SHAPE@LENGTH
Question 3
Question
What is the main reason to use geometry tokens instead of SHAPE@?
Answer
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Working with the full geometry objects of large datasets can be very slow
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You only need SHAPE@ to create new features, not to read properties of existing ones
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Geometry tokens give you access to the individual vertices of geometry objects, while SHAPE@ only gives you the entire geometry object
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Some feature classes do not have a SHAPE field and using geometry tokens is the only option
Question 4
Question
When using geometry tokens in a search cursor for single part polylines and polygons, what does the search cursor return for each row in the feature attribute table?
Answer
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an array of point objects
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an array containing an array of point objects
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a list of point objects
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a list containing a list of point objects
Question 5
Question
Consider the following script, in particular line 8 that uses getPart (0):
import arcpy
from arcpy import env
env.workspace = "C:/Data"
fc = "roads.shp"
cursor = arcpy.da.SearchCursor (fc, ["OID@", "SHAPE@"])
for row in cursor:
print ("Feature {0}: ".format (row[0]))
for point in row[1].getPart (0):
print ("{0}, {1}".format (point.X, point.Y))
Why is getPart (0) needed here, even if the features are all single part?
Answer
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For polylines and polygons, the cursor returns the parts of a geometry object as an array, so for single part features you need to get the first (and only) part
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If you don't use getPart, all vertices for the entire feature class would print together and you would not be able to tell which vertices belong to which feature.
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The use of getPart makes it possible to use the same script for point, polyline and polygon features.
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All geometry objects consist of arrays of points, so get at the individual points you need to examine the parts.
Question 6
Question
Which property(ies) of a geometry objects is (are) used to determine whether a specific feature is multipart or single part?
Answer
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partCount
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type
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isMultipart
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pointCount
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shapeType
Question 7
Question
Some polygon features contain 'holes'. When you work with geometry objects for such polygons, how can you determine whether these holes are present?
Answer
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the geometry property ringCount is greater than 1 for polygons with holes
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you can use the geometry property isExterior to determine whether an array of point objects is an exterior or interior ring
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the shapeType property of the geometry object is MultiPatch instead of Polygon
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the array of point objects for a feature contains 'null point objects' which seperate the exterior and interior rings
Question 8
Question
Consider a scenario where you write a script to create a new polyline out of a text file with coordinates for the vertices. You will need to use a cursor object to create new geometry objects. Which of the following is the correct line of code to set up your cursor object?
Answer
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cursor = arcpy.da.UpdateCursor(fc, ["SHAPE@"])
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cursor = arcpy.da.InsertCursor(fc, "SHAPE@XY")
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cursor = arcpy.da.InsertCursor(fc, "SHAPE@")
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cursor = arcpy.da.UpdateCursor(fc, ["SHAPE@XY"])
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cursor = arcpy.da.InsertCursor (fc, ["SHAPE@XY"])
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cursor = arcpy.da.UpdateCursors(fc, ["SHAPE@XY"])
Question 9
Question
Consider the following script to print the coordinates of the vertices of the features of a feature class.
import arcpy
from arcpy import env
env.workspace = "C:/Data"
fc = "features.shp"
cursor = arcpy.da.SearchCursor(fc, ["OID@", "SHAPE@"])
for row in cursor:
print ("Feature {0}: ".format(row[0]))
partnum = 0
for part in row[1]:
print ("Part {0}:".format(partnum))
for point in part:
print ("{0}, {1}".format(point.X, point.Y))
partnum += 1
For which types of datasets will this script work correctly? (check all that apply)
Answer
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Single-part point features
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Multi-part point features
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Multi-part polygon features with holes
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Multi-part polyline and polygon features
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Single-part polyline and polygon features
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Single-part polygon features with holes
Question 10
Question
Consider the following script to print the coordinates of the vertices of the features of a feature class.
import arcpy
from arcpy import env
env.workspace = "C:/Data"
fc = "features.shp"
cursor = arcpy.da.SearchCursor(fc, ["OID@", "SHAPE@"])
for row in cursor:
print ("Feature {0}: ".format(row[0]))
partnum = 0
for part in row[1]:
print ("Part {0}:".format(partnum))
for point in part:
print ("{0}, {1}".format(point.X, point.Y))
partnum += 1
Line 10 of the code reads 'for part in row[1]:'. Why does the code use row[1] instead of just row?
Answer
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because you only want to obtain the first part of the geometry object
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because the search cursor returns a list and row[1] obtains the geometry object
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because the script is only designed to work for single part features
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because the search cursor returns a list and row[1] obtains the list of coordinates
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because you want to start numbering the parts of each features at 1
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