topic Re: How can I transform a polygon into a point? in Map Advice Community Questions

How can I transform a polygon into a point?

GB — Thu, 16 Nov 2017 22:24:50 GMT

Hi!

I have a shapefile with polygons, but I want to transform these objects into points (example: I have the polygons with are the physical borders of a subset of school, I want to have point rather than the polygon of the building).

What can I use?

- feature to points doesn't suit me because it creates a new output, while I would like to keep the information I have in my original shapefile.

-I tried add geometry attributes, it runs successfully, but it doesn't not add the geometry attributes!!! Do you know why it happens?

Do you have other solutions?

Thank you!!

Re: How can I transform a polygon into a point?

DanPatterson_Retired — Thu, 16 Nov 2017 22:28:16 GMT

You will need to produce a new output of some kind. One of the easiest would be to calculate the X, Y (aka centroid) value for the center, then add it back in to the dataframe as an event layer saving to a point featureclass if you want

Re: How can I transform a polygon into a point?

GB — Thu, 16 Nov 2017 23:06:49 GMT

Thank you. Do you know why the add geometry attributesi is not woking? the tool runs successfully, but then in the table it doesn't add the geometry attributes!!!

Re: How can I transform a polygon into a point?

DanPatterson_Retired — Thu, 16 Nov 2017 23:50:27 GMT

show a screen grab of the table's first few rows. There is a Shape field isn't there?. There should be two new fields if you specified the centroid/center X and Y values

Re: How can I transform a polygon into a point?

JayantaPoddar — Fri, 17 Nov 2017 08:13:26 GMT

Feature to Point (Data Management) should work for you (Requires ArcGIS Desktop Advanced license). The attributes of the input features will be maintained in the output feature class. In case of multipart polygon, the centroid might lie outside the polygon.

I will say "Give it a try".

Re: How can I transform a polygon into a point?

XanderBakker — Sun, 12 Dec 2021 09:44:28 GMT

In case you do not have access to an Advance license you could create a tool that does this for you with a Basic license.(sorry for the Spanish interface)

first parameter is the polygon featureclass
second parameter is the output point featureclass
third parameter is the method

The code beneath looks like this:

#-------------------------------------------------------------------------------
# Name:        FeatureToPoint.py
# Purpose:     Convertir feature a punto
#
# Author:      xbakker
#
# Created:     02/03/2015
#-------------------------------------------------------------------------------
import arcpy
import os
import math

def main():

    # parameters
    fc_in = arcpy.GetParameterAsText(0)
    fc_out = arcpy.GetParameterAsText(1)
    method = arcpy.GetParameterAsText(2) # CENTROID, INSIDE

    # fld para poder hacer el join con la entrada
    fld_oid_in = "ORIG_FID"

    # geometria de salida
    geomtype = "POINT"
    sr = arcpy.Describe(fc_in).spatialReference

    # recreate fc_out based on fc_lines (in)
    ws_name, fc_name = os.path.split(fc_out)
    createFeatureClass(fc_out, fc_in, geomtype, sr)

    # add OID field
    arcpy.AddField_management(fc_out, fld_oid_in, "LONG")

    # cursors:
    cnt = 0
    flds_out = ("SHAPE@", fld_oid_in)
    with arcpy.da.InsertCursor(fc_out, flds_out) as curs_out:
        flds_in =("SHAPE@", "OID@")
        with arcpy.da.SearchCursor(fc_in, flds_in) as curs:
            for row in curs:
                feat = row[0]
                oid = row[1]

                # get point based on method
                pnt = getPoint(feat, method)

                # store point
                cnt += 1
                if cnt % 100 == 0:
                    arcpy.AddMessage("Procesando feature: {0}".format(cnt))
                curs_out.insertRow((pnt, oid, ))

    arcpy.AddMessage("{0} features procesados...".format(cnt))


def getPoint(feat, method):
    """Convertir feature a punto dependiendo del metodo y tipo de geometria"""

    pnt = None
    if method == "CENTROID" and feat.type == 'polygon':
        pnt = feat.centroid

    elif method == "CENTROID" and feat.type == 'polyline':
        pnt = CentroidPolyline(feat)

    elif method == "CENTROID" and feat.type == 'multipoint':
        # average x and y coordinates of all the points in the multipoint feature
        pnt = CentriodMultiPoint(feat)

    elif method == "INSIDE" and feat.type == 'polygon':
        pnt = feat.labelPoint

    elif method == "INSIDE" and feat.type == 'polyline':
        pntg = feat.positionAlongLine(0.5, True)
        pnt = pntg.firstPoint

    elif method == "INSIDE" and feat.type == 'multipoint':
        pnt = InsideMultiPoint(feat)

    return pnt


def InsideMultiPoint(feat):
    # punto mas cercano al centroid
    pnt_c = CentriodMultiPoint(feat)
    min_dist = 999999
    for pnt_mp in feat:
        dist = getDistance(pnt_mp, pnt_c)
        if dist < min_dist:
            pnt = arcpy.Point(pnt_mp.X, pnt_mp.Y)
            min_dist = dist
    return pnt

def CentriodMultiPoint(multipoint):
    lst_x = []
    lst_y = []
    for pnt in multipoint:
        lst_x.append(pnt.X)
        lst_y.append(pnt.Y)

    return arcpy.Point(sum(lst_x)/float(len(lst_x)), sum(lst_y)/float(len(lst_y)))


def CentroidPolyline(polyline):
    """weighted average x and y coordinates of the midpoints of all line segments in the line feature
       where the weight of a particular midpoint is the length of the correspondent line segment"""
    lst_x = []
    lst_y = []
    lst_length = []
    for part in polyline:
        prev_pnt = None
        for pnt_part in part:
            if prev_pnt is None:
                # skip
                prev_pnt = arcpy.Point(pnt_part.X, pnt_part.Y)
            else:
                dist = getDistance(pnt_part, prev_pnt)
                line = arcpy.Polyline(arcpy.Array([prev_pnt, pnt_part]))
                mid_pnt = line.positionAlongLine(0.5, True)
                lst_x.append(mid_pnt.firstPoint.X * dist)
                lst_y.append(mid_pnt.firstPoint.Y * dist)
                lst_length.append(dist)

    sum_dist = sum(lst_length)
    sum_x = sum(lst_x)
    sum_y = sum(lst_y)
    x = sum_x / sum_dist
    y = sum_y / sum_dist
    return arcpy.Point(x, y)

def createFeatureClass(fc_out, fc_in, geomtype, sr):
    ws_name, fc_name = os.path.split(fc_out)
    arcpy.CreateFeatureclass_management(ws_name, fc_name, geomtype, spatial_reference=sr)

def getDistance(pnt1, pnt2):
    return math.hypot(pnt1.X - pnt2.X, pnt1.Y - pnt2.Y)

if __name__ == '__main__':
    main()
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Re: How can I transform a polygon into a point?

GB — Wed, 29 Nov 2017 17:19:00 GMT

I followed Dan Petterson's tip, and in the original layer (polygons) I added to new fields, and then calculated the geometry (x coordinate of the centroids, y coordinate of the centroids). Now, I would like to visualize these points on the map, how can I do that? Probably you Dan had already explained that ("then add it back in to the dataframe as an event layer saving to a point featureclass if you want"), but can you please write the passages? Thank you.

Re: How can I transform a polygon into a point?

DanPatterson_Retired — Wed, 29 Nov 2017 18:56:53 GMT

Go to the File Menu, select Add Data, Add XY Data.... then specify the value for the X field (ie Longitude) and the Y field (Latitude).

Once you have the event layer, right-click on it and you can select Data, Export Data, then specify in the dialog whether you want it to go to a folder as a shapefile (don't forget the *.shp file extension) or put it into a geodatabase as a featureclass.

Re: How can I transform a polygon into a point?

GB — Wed, 29 Nov 2017 21:59:48 GMT

Hi, I tried it (also before writing the post), but it seems to me I can only select a table when using the ADD XY data. I'm using ARCGIS 10.5. I am working with a feature class containing polygons.

Re: How can I transform a polygon into a point?

DanPatterson_Retired — Wed, 29 Nov 2017 22:50:41 GMT

you are effectively selecting the table of a featureclass... just makesure you are working with the table closed and the table of contents active. It will use the table to produce the event layer if the table of contents is active. Whatever you are doing, you are doing the same thing which is why it isn't working. Add the table as and event layer, rightclick on that layer in the table of contents then export

Re: How can I transform a polygon into a point?

GB — Thu, 30 Nov 2017 10:23:11 GMT

I am sorry, but when I open add XY Data, I can only choose a table. The only way that I found to visualize the centroids was to go to data management tools, layers and table views, make xy event layers. But in this way I crreate a new output, and that is something I do not want to obtain.

Re: How can I transform a polygon into a point?

DanPatterson_Retired — Thu, 30 Nov 2017 11:38:53 GMT

The only way, through any method, that you can view the centroids of a polygon, is to create a new layer.

I guess the word 'transform' can be interpreted differently.
The 'keeping the attributes in the original shapefile' can definitely be accomplished using the process I have outlined
features to points was definitely the wrong tool
add geometry attributes is part of the 'event layer ' creation

So option 2.. using the 'event layer' creation work... once you have the event layer converted to a shapefile, you can simply toggle off the polygon layer and the visualization you desire will be complete, albeit with a new layer.

I guess this thread can be closed, although you don't like the answer

Re: How can I transform a polygon into a point?

XanderBakker — Thu, 30 Nov 2017 12:04:07 GMT

In support of what Dan Patterson has been saying:

You cannot change the feature type from polygon to point. Furthermore, you shouldn't! You can always create a new featureclass that represents the polygons as points, but you will never be able to get back to this more precise polygon representation based on the points if you overwrite the original polygons. In theory you can, by creating a temporal point featureclass from the polygons, delete the polygon featureclass and rename the points. But once again, you shouldn't!

Did you try the toolbox I posted earlier to create a new point featureclass from the polygons? It shouldn't be difficult.

Re: How can I transform a polygon into a point?

GB — Mon, 04 Dec 2017 15:03:54 GMT

I fogot to ask something in my previous reply.

Summing up: I added two fields in the original feature class (contening polygons), I calculated the X and Y coordinates of the centroid, I created a XY event by going to data management tools, layers and table views, make xy event. When I open the attribute table, I find two fields with the shape, and the geometry is polygon. (see attachment). Why is that happening? I can visualize points on the map.

Re: How can I transform a polygon into a point?

XanderBakker — Mon, 04 Dec 2017 15:55:38 GMT

This is very strange. When you use XY events they will always create point geometry.