topic Re: Creating 3D line from points with python in Python Questions

Creating 3D line from points with python

MartinSirkovsky — Tue, 16 Sep 2014 16:29:01 GMT

Hi.

I have a series of points with X,Y,Z coordinates. I am trying to create a polylines from the points. Points should be vertexes of the polyline and Z-Coordinate should be used to define the elevation of vertexes.

I have created a script which works, but the Z-Coordinate is lost on vertexes and is recorded as ZERO. I am sure that my script is correct because if I pass the Z-Coordinate into the M value, it is recorded correctly. The part of the script which creates the line can be seen below:

vertexArray = arcpy.Array()

for points in pointArray:

xCoord = valueX

yCoord = valueY

zCoord = valueZ

# valueZ is also passed to M dimension to test if there are some problems with values

currentPoint = arcpy.Point(valueX, valueY, valueZ, valueZ)

vertexArray.add(currentPoint)

newLineCursor = arcpy.da.InsertCursor(outputFc, ["SHAPE@"])

polyline = arcpy.Polyline(vertexArray)

newLineCursor.insertRow([polyline])

The script runs wihtout problems, and the polylines are created. But when I check in ArcMAP the polyline under sketch properties all the vertexes on line have null as Z-Coordinate (see image bellow).

I have just tested to convert points with arcpy.PointsToLine_management, and it works correctly. I could implement this in my script, but I am still curious as to why is Z-Coordinate not recorded properly with my script.

Thanks,

Martin

Re: Creating 3D line from points with python

IanMurray — Tue, 16 Sep 2014 17:29:47 GMT

Just a thought, since ArcMap is for viewing and editting 2-D features, perhaps you can only edit the x and y in an edit session in ArcMap, and Z values are not given. Try editting your 3-D line in ArcScene and see if it has a Z value.

Re: Creating 3D line from points with python

TimothyHales — Tue, 16 Sep 2014 17:34:50 GMT

Is the feature class z enabled?

Create Feature Class (Data Management)‌

has_z parameter

Re: Creating 3D line from points with python

MartinSirkovsky — Tue, 16 Sep 2014 18:17:46 GMT

Yes it is Z enabled. You can see it at the image I have attached, that there is a z-coordinate.

You can edit Z values in ArcMap by typing z values in sketch properties.

Re: Creating 3D line from points with python

MartinSirkovsky — Tue, 16 Sep 2014 19:25:30 GMT

I have tried "PointsToLine_management" which almost does what I need it to do. And that tool works in ArcMap. So I guess the script should work. Is it a bug?

Re: Creating 3D line from points with python

NeilAyres — Wed, 17 Sep 2014 08:58:53 GMT

I am using v10.2 and regularly create polylineZM's from coordinates in python. So no bugs.

Be aware that when you create the geometry you should specify the SR of that geometry.

But that is unlikely to be the issue here.

Re: Creating 3D line from points with python

MartinSirkovsky — Wed, 17 Sep 2014 09:36:38 GMT

I have tried a different approach and got it to work. Actually what I am trying to accomplish is to convert line file to 3D based on points. As it is not possible to snap 3D in ArcMap the lines constructed from surveying points in ArcMap are placed on zero elevation. After the lines are constructed, I am using the point file to change the elevation on the vertexes to the original one. The working script can be seen here:

import arcpy

shapeFileFolder = "folder where the files are located"

fileToProcess = "line or polygon file"

fileWith3DPoints = "file with 3D points which were used to construct the lines"

arcpy.env.workspace = shapeFileFolder

arcpy.env.overwriteOutput = True

def convertTo3D(fc, zPoints):

# Dictionary to hold the point coordinates (key: x,y coord, value: z coord)

zCoordDict = {}

# Create an array which will hold geometries of point feature class

fields = ["SHAPE@X","SHAPE@Y","SHAPE@Z"]

with arcpy.da.SearchCursor(zPoints, fields) as cursor:

for row in cursor:

# round the coordinates to 3 decimal places

xCoord = round(row[0], 3)

yCoord = round(row[1], 3)

zCoord = round(row[2], 3)

# add key:value for current point to the dictionary

zCoordDict[str(xCoord) + "," + str(yCoord)] = zCoord

# Update Z coord in input file

fields = ["SHAPE@X","SHAPE@Y","SHAPE@Z"]

cursor = arcpy.da.UpdateCursor(fc, fields, None, None, True)

for row in cursor:

# Get x,y coordinates of current point

xCoord = str(round(row[0],3))

yCoord = str(round(row[1],3))

newZCoord = zCoordDict[xCoord +"," + yCoord]

print "New Z coordinate for current point is %s" % (newZCoord)

row[2] = newZCoord

cursor.updateRow(row)

# Run the function

convertTo3D(fileToProcess, fileWith3DPoints)

Re: Creating 3D line from points with python

MichaelFell — Sun, 07 Jun 2015 23:52:15 GMT

When you create a 3D polyline object, you have to set the 'has_Z' property to True --

arcpy.Polyline (inputs, {spatial_reference}, {has_z}, {has_m})

When you do this the polyline will retain the Z coordinates in your points.

Re: Creating 3D line from points with python

XanderBakker — Mon, 08 Jun 2015 03:09:19 GMT

Very true what Michael Fell mentions. You can see how to convert 3D point to 3D lines with python code in the thread below:

Convert 3D points to 3D lines (underground well data)

Re: Creating 3D line from points with python

TanyaKnowles2 — Mon, 14 Dec 2015 13:29:57 GMT

Just a point of information here - I was writing a script to write some 3D polylines to an empty feature class. I was having trouble adding the Z value, pretty much the same as Martin Sirkovsky's initial post. I tried setting the 'has_z' to true when I created a polyline, but I was getting an error saying that attribute was read only. The solution: despite both being optional parameters you need to have a spatial reference value set before you can set has_z to true.

Re: Creating 3D line from points with python

DanielBean1 — Tue, 21 May 2019 16:21:54 GMT

Michael Fells point is important, but be aware that there is some strange behavior in arcpy (as of 10.4.1)

polyline = arcpy.Polyline(line_array, sr, True) # This works

.. but this fails

polyline = arcpy.Polyline(line_array, spatial_reference=sr, has_z=True)

If you supply the arguments by position it works, but if you use keyword args it fails.