topic Re: Extend Line up to polygon feature in Python Questions

Extend Line up to polygon feature

Sai_AnandPeketi1 — Fri, 14 Apr 2017 16:52:12 GMT

Hi everyone,

I've some set of points which I'm joining to make a line. Refer the Picture below.

The problem I'm facing is there are no points(elevation points) on the polygon (River Bank). Is there any way of extending the line to the polygon?

At present m using Extend line to layer, but it taking too much of time and inconsistent in the lines. Refer the Picture below.

Re: Extend Line up to polygon feature

XanderBakker — Sun, 16 Apr 2017 19:10:02 GMT

Can you share a sample of your data (points, lines and polygon)? The situations in the first image do not correspond to the situations in the second image (probably to do with the sequence of the points) and it would be good to know what is going on. I see some similarity with this thread Points to line in Arcmap , but you have already defined a way to connect the points into a line. There are several ways of extending the line to the river banks:

extending the first and last vertex pair (using the same direction as defined by the vertex pairs)
simply snapping the first and last points to the nearest point (edge) on the river bank

Both are highly depend on the "quality" of the input line. So if the line was created correctly, this should not be a problem. However the results from your second image suggest differently.

Re: Extend Line up to polygon feature

RebeccaStrauch__GISP — Sun, 16 Apr 2017 19:45:32 GMT

I agree with Xander's comments and link. I haven't used the ArcScript tool you mentioned, so I'm not sure what is too slow, but you may want to look into using Map Topology to help you find the error, including the part of changing multiple issues at once. But unless you do know that all the lines are geometrically clean, you will want to be carefully on doing anything in bulk. You may want to do smaller batches so you can make sure other issues are not introduced.

Exercise 4b: Using geodatabase topology to fix line errors—Help | ArcGIS Desktop

Creating a map topology—Help | ArcGIS Desktop

Re: Extend Line up to polygon feature

Sai_AnandPeketi1 — Sun, 16 Apr 2017 20:29:22 GMT

Yes, I checked the Point to line . Actually, Same data I am also working for creating a line. We want to create a line feature from elevation point data. That line should touch the river banks all this we need automated process. The Second image which I am using the Extend line to layer tool for extend the output which got from the point to line tool. But Its taking time for 200 feature and getting geometrically errors.

Do you have any idea or script that create a line with the elevation point and line extend up to river banks.

Thanks for help.

Re: Extend Line up to polygon feature

Sai_AnandPeketi1 — Sun, 16 Apr 2017 20:34:07 GMT

Any python script that fixing the topological errors. Need in automated process. Have a huge amount of data for study. So, it difficult to run this tool manual.

Thanks for help.

Re: Extend Line up to polygon feature

JoshuaBixby — Mon, 17 Apr 2017 01:52:50 GMT

How is this question different than https://community.esri.com/message/678558-join-a-line-to-a-polygon?sr=search&searchId=2df49d12-d2a5-4adc-81d9-c73827318d3a&searchIndex=0‌?

Re: Extend Line up to polygon feature

Sai_AnandPeketi1 — Mon, 17 Apr 2017 07:24:16 GMT

Nothing was different but getting error with the script. Please find the sample data,

Re: Extend Line up to polygon feature

JoshuaBixby — Sun, 12 Dec 2021 05:39:26 GMT

I just downloaded the sample data, and ran my code from the Draw a Line to the nearest Polygon thread, and it ran without any errors and did exactly what you wanted. I did have to increase the dist value since you are using State Plane, and the gaps between the lines and river banks are greater than 100 feet.

Here is the code that worked for me, using your 2 shape files (load the shape files into ArcMap first and run from interactive Python window):

>>> import math
>>> dist = 500
>>> 
>>> fc_line = "Pointoline"
>>> fc_poly = "RB_23"

>>> with arcpy.da.SearchCursor(fc_poly, "SHAPE@") as scur:
...     for poly, in scur:
...         boundary = poly.boundary()
...         arcpy.SelectLayerByLocation_management(fc_line, "WITHIN", poly)
...         with arcpy.da.UpdateCursor(fc_line, "SHAPE@") as ucur:
...             for line, in ucur:
...                 arr, = line.getPart()
...                 SR = line.spatialReference
...                 
...                 p1, p2 = arr[:2]
...                 angle = math.atan2(p2.Y - p1.Y, p2.X - p1.X)
...                 p = arcpy.Point(p1.X - dist * math.cos(angle),
...                                 p1.Y - dist * math.sin(angle))
...                 arr.insert(0, p)
...                 
...                 pn1, pn = arr[-2:]
...                 angle = math.atan2(pn.Y - pn1.Y, pn.X - pn1.X)
...                 p = arcpy.Point(pn.X + dist * math.cos(angle),
...                                 pn.Y + dist * math.sin(angle))
...                 arr.append(p)
...                 
...                 line = arcpy.Polyline(arr, SR)
...                 line = line.cut(boundary)[1]
...                 ucur.updateRow([line])
...                 
>>>‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: Extend Line up to polygon feature

XanderBakker — Sun, 12 Dec 2021 05:39:28 GMT

The option provided by Joshua Bixby is a very good one. It takes the direction of the first and last part of the line and extends it to the polygon boundary. As an alternative you can simply snap the first and last point to polygon boundary (see code below).

#-------------------------------------------------------------------------------
# Name:       snapline2polygon.py
# Purpose:
#
# Author:      xbakker
#
# Created:     17/04/2017
#-------------------------------------------------------------------------------

def main():
    print "Start process..."
    import arcpy
    fc_line = r'C:\GeoNet\SnapLine2Polygon\Pointoline.shp'
    fc_pol = r'C:\GeoNet\SnapLine2Polygon\RB_23.shp'
    fc_out = r'C:\GeoNet\SnapLine2Polygon\snapped_lines.shp'

    # fech polygon and get perimeter
    print "Get polygon and boundary"
    polygon = arcpy.da.SearchCursor(fc_pol, ('SHAPE@')).next()[0]
    boundary = polygon.boundary()

    print "start loop..."
    lst_feats = []
    cnt = 0
    with arcpy.da.SearchCursor(fc_line, ('SHAPE@')) as curs:
        for row in curs:
            cnt += 1
            if cnt % 10 == 0:
                print " - processing line", cnt
            polyline = row[0]
            pnt1 = polyline.firstPoint
            pnt2 = polyline.lastPoint

            pntg1_snap = boundary.snapToLine(pnt1)
            pntg2_snap = boundary.snapToLine(pnt2)
            polyline_out = ExtendPolyline(polyline, pntg1_snap.firstPoint, pntg2_snap.firstPoint)

            lst_feats.append(polyline_out)

    # store results
    print "store results..."
    arcpy.CopyFeatures_management(lst_feats, fc_out)


def ExtendPolyline(polyline, pnt1, pnt2):
    # will snap first and last line to nearest part of given polyline
    # does not account for small segments!
    sr = polyline.spatialReference
    lst_pnts = []
    for part in polyline:
        for pnt in part:
            lst_pnts.append(pnt)

    lst_pnts.insert(0, pnt1)
    lst_pnts.append(pnt2)
    return arcpy.Polyline(arcpy.Array(lst_pnts), sr)


if __name__ == '__main__':
    main()
‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

This will produce errors when you have small segments and the first of last point is closer to the wrong side of the polygon boundary:

To avoid this you would have to edit the line data and create the correct lines to be extended or use the logic suggested by Joshua.

Re: Extend Line up to polygon feature

Sai_AnandPeketi1 — Mon, 17 Apr 2017 17:08:26 GMT

But, I am getting error at p1,p2 = arr[:2] and using arcmap 10.3

Runtime error
Traceback (most recent call last):
File "<string>", line 10, in <module>
File "c:\program files (x86)\arcgis\desktop10.3\arcpy\arcpy\arcobjects\mixins.py", line 161, in __getitem__
return convertArcObjectToPythonObject(self._arc_object.GetObject(index))
AttributeError: Array: Error in parsing arguments for GetObject

Thanks for help.

Re: Extend Line up to polygon feature

JoshuaBixby — Mon, 17 Apr 2017 18:24:06 GMT

I am using ArcGIS 10.5, which explains part of the issue. Prior to ArcGIS 10.4.x, ArcPy Array objects supported indexing but not slicing, hence the error message you are seeing running my code.

Try replacing line 16 with:

p1, p2 = arr[0], arr[1]

and replacing line 22 with:

pn1, pn = arr[len(arr)-2], arr[len(arr)-1]

Re: Extend Line up to polygon feature

Sai_AnandPeketi1 — Mon, 17 Apr 2017 19:23:24 GMT

And I have Z values in line extent. While updating the geometry those are not update geometry. So, Please help to get those Z-Values.

Thanks for the help

Re: Extend Line up to polygon feature

XanderBakker — Sun, 12 Dec 2021 05:39:32 GMT

In the code sample I provided, this can be done pretty easy changing the function "ExtendPolyline" inserting line 10 setting the Z values for start and end point of the line (at the polygon boundary) to 0 (assuming this is correct) and enabling Z values for the polygon on line 13 in the example below:

def ExtendPolyline(polyline, pnt1, pnt2):
    # will snap first and last line to nearest part of given polyline
    # does not account for small segments!
    sr = polyline.spatialReference
    lst_pnts = []
    for part in polyline:
        for pnt in part:
            lst_pnts.append(pnt)

    pnt1.Z, pnt2.Z = 0, 0
    lst_pnts.insert(0, pnt1)
    lst_pnts.append(pnt2)
    return arcpy.Polyline(arcpy.Array(lst_pnts), sr, True, False)‍‍‍‍‍‍‍‍‍‍‍‍‍

The result viewed in 3D looks like this:

I do notice that near the shore lines (polygon boundary) some values have a Z value greater than 0. Are you sure that the measure Z values of the points used to create the profile lines correspond to the polygon boundary (same date)?

In case you want to continue with the code provided by Joshua Bixby it will be a little more complex since you can't just do this by simply adding the Z=0 property to the point "p"(lines 4 and 10) in the snippet below and changing line 13 to make it Z-aware:

                p1, p2 = arr[0], arr[1]
                angle = math.atan2(p2.Y - p1.Y, p2.X - p1.X)
                p = arcpy.Point(p1.X - dist * math.cos(angle),
                                p1.Y - dist * math.sin(angle), 0)
                arr.insert(0, p)

                pn1, pn = arr[len(arr)-2], arr[len(arr)-1]
                angle = math.atan2(pn.Y - pn1.Y, pn.X - pn1.X)
                p = arcpy.Point(pn.X + dist * math.cos(angle),
                                pn.Y + dist * math.sin(angle), 0)
                arr.append(p)

                line = arcpy.Polyline(arr, SR, True, False)
                line = line.cut(boundary)[1]
                ucur.updateRow([line])‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

The line start and end before cutting would have the Z set to 0, but will no have as result that the Z value at the shore will be 0. As an alternative, you cut the 3D line, and afterwards, read out the first and last point, set the Z value to 0 and insert them back in the array and create the final 3D polyline:

import math
dist = 500

fc_line = "Pointoline"
fc_poly = "RB_23"

with arcpy.da.SearchCursor(fc_poly, "SHAPE@") as scur:
    for poly, in scur:
        boundary = poly.boundary()
        arcpy.SelectLayerByLocation_management(fc_line, "WITHIN", poly)
        with arcpy.da.UpdateCursor(fc_line, "SHAPE@") as ucur:
            for line, in ucur:
                arr, = line.getPart()
                SR = line.spatialReference

                p1, p2 = arr[0], arr[1]
                angle = math.atan2(p2.Y - p1.Y, p2.X - p1.X)
                p = arcpy.Point(p1.X - dist * math.cos(angle),
                                p1.Y - dist * math.sin(angle))
                arr.insert(0, p)

                pn1, pn = arr[len(arr)-2], arr[len(arr)-1]
                angle = math.atan2(pn.Y - pn1.Y, pn.X - pn1.X)
                p = arcpy.Point(pn.X + dist * math.cos(angle),
                                pn.Y + dist * math.sin(angle))
                arr.append(p)

                line = arcpy.Polyline(arr, SR, True, False)
                line = line.cut(boundary)[1]

                arr, = line.getPart()
                p1, pn = arr[0], arr[len(arr)-1]
                p1.Z, pn.Z = 0, 0
                arr.insert(0, p1)
                arr.append(pn)
                line = arcpy.Polyline(arr, SR, True, False)

                ucur.updateRow([line])‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: Extend Line up to polygon feature

JoshuaBixby — Thu, 20 Apr 2017 13:43:39 GMT

Nice work, the OP has gotten lots of good work out of GeoNet contributors. It is hard to pass up an interesting, and a bit challenging, of a question.

Re: Extend Line up to polygon feature

Sai_AnandPeketi1 — Tue, 25 Apr 2017 21:33:15 GMT

Joshua, I increased the distance. But in some line are not touching with the riverbank.Please have a look.

Re: Extend Line up to polygon feature

JoshuaBixby — Thu, 27 Apr 2017 00:32:52 GMT

I re-downloaded the sample data, and it doesn't include any of these problematic lines. To give any specific suggestions, I will need to see the data behind some of these problem lines. Can you upload a second sample data set of the area in the image?

Re: Extend Line up to polygon feature

edlaanil — Tue, 15 Feb 2022 18:54:21 GMT

Feature to ploygon with two input polylines to convert to polygon getting error from python script in dot net arc gis pro

kindly help me