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I have a polyline feature with many segments (polyline split at vertices).
I plan to record angle values to attribute table per each polyline segment and assign it to point features.
I need to calculate angle value between segments of a polyline (Get value calculated angle less 180 ). 
.
Here almost is what I need: Calculating incidence angle of polyline?
Here's a little script I put together to read a line and write points at vertices:
import os, sys, arcpy, math
# read http://help.arcgis.com/En/Arcgisdesktop/10.0/Help/index.html#/Adding_a_script_tool/00150000001r000000/
InLines = sys.argv[1] # input:Feature Class
OutFile = sys.argv[2] # output:Shapefile
# using OS functions:
# assume OutFile is "C:\\this\\path\\file.shp"
# then os.path.dirname(OutFile) = C:\this\path
# and os.path.basename(OutFile) = file.shp
# http://help.arcgis.com/En/Arcgisdesktop/10.0/Help/index.html#//00170000002p000000
arcpy.CreateFeatureclass_management(os.path.dirname(OutFile),os.path.basename(OutFile),"POINT")
arcpy.AddField_management(OutFile,"ANGLE","DOUBLE") # Add the angle field or there's no point doing this..
# you might want to do something like this:
# SR = arcpy.SpatialReference(28356) # use EPSG/SRID code here to create a spatial reference
# arcpy.DefineProjection_management(OutFile,SR), but you can do that later..
# create an insert cursor to write the output and a search cursor to read the input
with arcpy.da.InsertCursor(OutFile,["SHAPE@XY","ANGLE"]) as ICur:
with arcpy.da.SearchCursor(InLines,"SHAPE@") as SCur:
for ThisFeature in SCur:
# loop for every feature..
# read the geometries like http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//002z0000001t000000
Geom = ThisFeature[0] # should be a polyline but polygons will work too
Parts = range(Geom.partCount) #http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//000v000000n2000000
# polygons and polygons can be made of many parts
# so it's important to read each part (it's usually only 1 part)
for prt in Parts:
ThisPart = Geom.getPart(prt) # ThisPart is a Geometry object
PointCount = ThisPart.count # http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Array/000v0000005r000000/
qPointsRange = range(1,PointCount -1) # range from 2nd to 2nd last
for point in qPointsRange:
ThisPoint = ThisPart.getObject(point) # ThisPoint is a Point object http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Point/000v000000mv000000/
X = ThisPoint.X # this vertex X and Y
Y = ThisPoint.Y
prePnt = ThisPart.getObject(point -1) # the vertex before this one
pstPnt = ThisPart.getObject(point +1) # the vertex after this one
# http://stackoverflow.com/questions/1211212/how-to-calculate-an-angle-from-three-points
# atan2(P2.y - P1.y, P2.x - P1.x) - atan2(P3.y - P1.y, P3.x - P1.x)
Angle = math.atan2(Y-prePnt.Y,X-prePnt.X) - math.atan2(pstPnt.Y - prePnt.Y,pstPnt.X - prePnt.X)
# I'm not sure if that's what you're after but relatively speaking that's the easy part
# to change if you're not happy with the angles. I am fairly sure the answer is in radians.
ICur.insertRow(((X,Y),Angle)) # write the point to the new shape file
I can't vouch for the maths on the last few lines but there's a fairly good skeleton there to work with.
The key is to get this vertex, the one before and the one after and through Pythagorean mathematics the interior angle can be determined.
math.atan function but when the true angle was about 175 degrees it could count it as 5 degrees. I turned to a bulky cosine function but it did rigth calculations.
Apr 4, 2018 at 13:54
Congrats to @Michael Stimson for the great script. I stumbled upon the thread when trying to tackle a similar problem and -after some test runs performed in a dataset of my own- I believe that the following corrections should be made:
# create an insert cursor to write the output and a search cursor to read the input
with arcpy.da.InsertCursor(OutFile,["SHAPE@XY","ANGLE"]) as ICur:
with arcpy.da.SearchCursor(InLines,"SHAPE@") as SCur:
for ThisFeature in SCur:
# loop for every feature..
# read the geometries like http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//002z0000001t000000
Geom = ThisFeature[0] # should be a polyline but polygons will work too
Parts = range(Geom.partCount) #http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//000v000000n2000000
# polygons and polygons can be made of many parts
# so it's important to read each part (it's usually only 1 part)
for prt in Parts:
ThisPart = Geom.getPart(prt) # ThisPart is a Geometry object
PointCount = ThisPart.count # http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Array/000v0000005r000000/
qPointsRange = range(1,PointCount -1) # range from 2nd to 2nd last
for point in qPointsRange:
ThisPoint = ThisPart.getObject(point) # ThisPoint is a Point object http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Point/000v000000mv000000/
X = ThisPoint.X # this vertex X and Y
Y = ThisPoint.Y
prePnt = ThisPart.getObject(point -1) # the vertex before this one
pstPnt = ThisPart.getObject(point +1) # the vertex after this one
# http://stackoverflow.com/questions/1211212/how-to-calculate-an-angle-from-three-points
# atan2(P2.y - P1.y, P2.x - P1.x) - atan2(P3.y - P1.y, P3.x - P1.x)
#Angle = math.degrees(math.atan2(Y-prePnt.Y,X-prePnt.X) - math.atan2(pstPnt.Y - prePnt.Y,pstPnt.X - prePnt.X))
Angle = math.degrees(math.atan2(prePnt.Y-Y,prePnt.X-X) - math.atan2(pstPnt.Y - Y,pstPnt.X - X))
if Angle > 0:
if Angle < 180:
Angle = Angle
else:
Angle = 360 -Angle
else:
if abs(Angle) < 180:
Angle = abs(Angle)
else:
Angle = 360 - abs(Angle)
ICur.insertRow(((X,Y),Angle)) # write the point to the new shape file
