Consider the following script, the polygon is a simple one with a hole inside: import arcpy poly1 = arcpy . FromWKT ( "POLYGON ((35 10, 45 45, 15 40, 10 20, 35 10), (20 30, 35 35, 30 20, 20 30))" ) print ( poly1 . isMultipart ) print ( poly1 . partCount ) The result I get is >>> True 1 So is a polygon "multipart" if it has holes? ArcGIS Data Reviewer does not agree. Thanks ArcGIS Desktop 10.5.1

I think you mean that is one of your ST point geometries pt = arcpy . Point ( ) pg = arcpy . PointGeometry ( pt ) pg . WKT 'POINT (0 0)' # because pt . WKT ( ) Traceback ( most recent call last ) : File " " , line 1 , in module > pt . WKT ( ) AttributeError : 'Point' object has no attribute 'WKT'

nav[aria-label="Primary Navigation"] { padding: 0; & ul { list-style: none; width: 100%; display: flex; flex-direction: row; justify-content: start; align-items: start; gap: 30px; padding: 0; & li { margin: 0; } & ul li { list-style: none; } } }

Is a polygon with a hole a multipart polygon?

EidurEidsson

Consider the following script, the polygon is a simple one with a hole inside:

<SPAN class="keyword token">import</SPAN> arcpy

poly1 <SPAN class="operator token">=</SPAN> arcpy<SPAN class="punctuation token">.</SPAN>FromWKT<SPAN class="punctuation token">(</SPAN><SPAN class="string token">"POLYGON ((35 10, 45 45, 15 40, 10 20, 35 10), (20 30, 35 35, 30 20, 20 30))"</SPAN><SPAN class="punctuation token">)</SPAN>

<SPAN class="keyword token">print</SPAN><SPAN class="punctuation token">(</SPAN>poly1<SPAN class="punctuation token">.</SPAN>isMultipart<SPAN class="punctuation token">)</SPAN>
<SPAN class="keyword token">print</SPAN><SPAN class="punctuation token">(</SPAN>poly1<SPAN class="punctuation token">.</SPAN>partCount<SPAN class="punctuation token">)</SPAN>‍‍‍‍‍‍<SPAN class="line-numbers-rows"><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN></SPAN>

The result I get is

>>>
True
1

So is a polygon "multipart" if it has holes? ArcGIS Data Reviewer does not agree.

Thanks

ArcGIS Desktop 10.5.1

Finde mehr Beiträge mit dem Tag

Accepted answers

All comments

JoshuaBixby

You are right, I am interested in point geometry and not point. What most of the world calls "point", Esri calls "point geometry" because Esri calls vertices points.

VinceAngelo

You wouldn't. But if you query a table with null geometries, a None would be returned for the row's array element where the PointGeometry would result.

- V

DanPatterson_Retired

I think you mean that is one of your ST point geometries

pt <SPAN class="operator token">=</SPAN> arcpy<SPAN class="punctuation token">.</SPAN>Point<SPAN class="punctuation token">(</SPAN><SPAN class="punctuation token">)</SPAN>
pg <SPAN class="operator token">=</SPAN> arcpy<SPAN class="punctuation token">.</SPAN>PointGeometry<SPAN class="punctuation token">(</SPAN>pt<SPAN class="punctuation token">)</SPAN>
pg<SPAN class="punctuation token">.</SPAN>WKT<SPAN class="string token">'POINT (0 0)'</SPAN>‍‍‍‍

<SPAN class="comment token"># because</SPAN>

pt<SPAN class="punctuation token">.</SPAN>WKT<SPAN class="punctuation token">(</SPAN><SPAN class="punctuation token">)</SPAN>
Traceback <SPAN class="punctuation token">(</SPAN>most recent call last<SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">:</SPAN>

&nbsp; File <SPAN class="string token">"<ipython-input-30-6f7eed26629f>"</SPAN><SPAN class="punctuation token">,</SPAN> line <SPAN class="number token">1</SPAN><SPAN class="punctuation token">,</SPAN> <SPAN class="keyword token">in</SPAN> <SPAN class="operator token"><</SPAN>module<SPAN class="operator token">></SPAN>
&nbsp;&nbsp;&nbsp; pt<SPAN class="punctuation token">.</SPAN>WKT<SPAN class="punctuation token">(</SPAN><SPAN class="punctuation token">)</SPAN>

AttributeError<SPAN class="punctuation token">:</SPAN> <SPAN class="string token">'Point'</SPAN> object has no attribute <SPAN class="string token">'WKT'</SPAN><SPAN class="line-numbers-rows"><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN></SPAN>

DanPatterson_Retired

It is possible though

a <SPAN class="operator token">=</SPAN> np<SPAN class="punctuation token">.</SPAN>array<SPAN class="punctuation token">(</SPAN><SPAN class="punctuation token">[</SPAN>np<SPAN class="punctuation token">.</SPAN>nan<SPAN class="punctuation token">,</SPAN> np<SPAN class="punctuation token">.</SPAN>nan<SPAN class="punctuation token">,</SPAN> np<SPAN class="punctuation token">.</SPAN>nan<SPAN class="punctuation token">,</SPAN> np<SPAN class="punctuation token">.</SPAN>nan<SPAN class="punctuation token">]</SPAN><SPAN class="punctuation token">)</SPAN>

p <SPAN class="operator token">=</SPAN> arcpy<SPAN class="punctuation token">.</SPAN>Point<SPAN class="punctuation token">(</SPAN><SPAN class="punctuation token">)</SPAN>
<SPAN class="operator token"><</SPAN>Point <SPAN class="punctuation token">(</SPAN><SPAN class="number token">0.0</SPAN><SPAN class="punctuation token">,</SPAN> <SPAN class="number token">0.0</SPAN><SPAN class="punctuation token">,</SPAN> <SPAN class="comment token">#, #)></SPAN>

p<SPAN class="punctuation token">.</SPAN>X<SPAN class="punctuation token">,</SPAN> p<SPAN class="punctuation token">.</SPAN>Y<SPAN class="punctuation token">,</SPAN> p<SPAN class="punctuation token">.</SPAN>Z<SPAN class="punctuation token">,</SPAN> p<SPAN class="punctuation token">.</SPAN>M <SPAN class="operator token">=</SPAN> a

p
<SPAN class="operator token"><</SPAN>Point <SPAN class="punctuation token">(</SPAN>nan<SPAN class="punctuation token">,</SPAN> nan<SPAN class="punctuation token">,</SPAN> nan<SPAN class="punctuation token">,</SPAN> nan<SPAN class="punctuation token">)</SPAN><SPAN class="operator token">></SPAN><SPAN class="line-numbers-rows"><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN></SPAN>

JoshuaBixby

My preference would be for an empty point:

<SPAN class="operator token">>></SPAN><SPAN class="operator token">></SPAN> <SPAN class="keyword token">import</SPAN> arcpy
<SPAN class="operator token">>></SPAN><SPAN class="operator token">></SPAN>
<SPAN class="operator token">>></SPAN><SPAN class="operator token">></SPAN> <SPAN class="comment token"># if I could wave a wand</SPAN>
<SPAN class="operator token">>></SPAN><SPAN class="operator token">></SPAN> pt <SPAN class="operator token">=</SPAN> arcpy<SPAN class="punctuation token">.</SPAN>Point<SPAN class="punctuation token">(</SPAN><SPAN class="punctuation token">)</SPAN>
<SPAN class="operator token">>></SPAN><SPAN class="operator token">></SPAN> pt<SPAN class="punctuation token">.</SPAN>WKT
<SPAN class="string token">'POINT EMPTY'</SPAN><SPAN class="line-numbers-rows"><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN></SPAN>

XanderBakker

Just wondering... how would you create a "PointGeometry with value of None"?

If I try:

pntg <SPAN class="operator token">=</SPAN> arcpy<SPAN class="punctuation token">.</SPAN>PointGeometry<SPAN class="punctuation token">(</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="line-numbers-rows"><SPAN>‍</SPAN></SPAN>

pntg <SPAN class="operator token">=</SPAN> arcpy<SPAN class="punctuation token">.</SPAN>PointGeometry<SPAN class="punctuation token">(</SPAN>None<SPAN class="punctuation token">)</SPAN><SPAN class="line-numbers-rows"><SPAN>‍</SPAN></SPAN>

it will throw:

RuntimeError: Object: CreateObject cannot create geometry from inputs

If I provide a "Nominal Point" it will be valid:

pntg <SPAN class="operator token">=</SPAN> arcpy<SPAN class="punctuation token">.</SPAN>PointGeometry<SPAN class="punctuation token">(</SPAN>arcpy<SPAN class="punctuation token">.</SPAN>Point<SPAN class="punctuation token">(</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">)</SPAN>
<SPAN class="keyword token">print</SPAN> pntg<SPAN class="punctuation token">.</SPAN>firstPoint
<SPAN class="comment token"># 0 0 NaN NaN</SPAN>

buf <SPAN class="operator token">=</SPAN> pntg<SPAN class="punctuation token">.</SPAN>buffer<SPAN class="punctuation token">(</SPAN><SPAN class="number token">1</SPAN><SPAN class="punctuation token">)</SPAN>
<SPAN class="keyword token">print</SPAN> buf<SPAN class="punctuation token">.</SPAN>area
<SPAN class="comment token"># 3.14159265359</SPAN>
<SPAN class="line-numbers-rows"><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN></SPAN>

DanPatterson_Retired

I know it is nominally null I just prefer Point(nan, nan, nan, nan)

VinceAngelo

That's not a null point so much as a nominal Point. A null point would be a PointGeometry with value of None.

Point corresponds to SE_POINT3D in the 'C' API, which is a simple struct type

DanPatterson_Retired

let's not forget, that there are bigger problems with the geometry model... a null point has X and Y coordinates of

<SPAN class="keyword token">import</SPAN> arcpy

arcpy<SPAN class="punctuation token">.</SPAN>Point<SPAN class="punctuation token">(</SPAN><SPAN class="punctuation token">)</SPAN>
<SPAN class="operator token"><</SPAN>Point <SPAN class="punctuation token">(</SPAN><SPAN class="number token">0.0</SPAN><SPAN class="punctuation token">,</SPAN> <SPAN class="number token">0.0</SPAN><SPAN class="punctuation token">,</SPAN> <SPAN class="comment token">#, #)></SPAN><SPAN class="line-numbers-rows"><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN></SPAN>

maybe the basics before rings

JoshuaBixby

Xander Bakker‌, I love the Freudian slip

"parts" of an inferior geometry dimension (like rings or lines)

EidurEidsson

I suspect isMultipart (and its description) is inherited from Geometry, hence the problem (it works fine with multipoints and polylines! why not polygons too?).

A soft landing would be:

1) Keep partCount as it is

2) Keep isMultipart but change the description.and mark as deprecated

3) Add 0...* replacements

Hard landing (if I'm right about the inheritance):

Override isMultipart to exclude interior rings; keep the description

DanPatterson_Retired

I agree, multipart should be separate, clockwise oriented geometry, whether they overlap or not (which is possible).

A counterclockwise ring within a clockwise ring should be 'hasholes' and that the number of 'holes' should be tracked at the same time as the number of parts.

In this way I could have a 3 part polygon, the first part could have 2 holes, the second part might have no holes, while the third part could have any number of holes (0 to n)

I would want to know this without me having to go through hoops, which I currently do.

It may not be as 'cool' as other stuff... but this is geometry, and fundamentally it is geometry that is used to answer questions.

Vector geometry has been ignored for too long. I can't even draw a 3D vertical cliff in 3D so that an xy coordinate can have 2 or more z-values. Not extrusion, ... actual geometry.

Rings, holes, they are the tip of the iceberg, but we should start somewhere.

Changes?????

Help file ...definitely.

Software behaviour... definitely

XanderBakker

Hi Dan Patterson‌, Vince Angelo‌ and Joshua Bixby‌,

I made a note at the help page with a link to this thread today and Jim Barry‌ contacted me directly after, asking what a good description could be or what should be changed at the help page (or if this is something that should be changed in the software)?

IMHO I think that when you talk about parts (in case of a polygon) this would refer to the number of individual disconnected areas in a single feature, and should not refer to "parts" of an inferior geometry dimension (like rings or lines). Maybe an addition property like "hasHoles" could be useful, however this could lead to unfortunate misspellings .

Since I consider that each one of you has more experience in this field, my question to you guys is, what suggestions do you have to obtain a clear explanation at the help page or is there something that should be changed in the behavior of the software?

JoshuaBixby

Both Dan Patterson‌ and myself have touched on this topic here and there on GeoNet in the past. You might find a blog post I a couple years back informative: /blogs/tilting/2016/02/20/the-single-multipart-polygons-with-interior-boundaries.

I spent some time trying the example above in different spatial systems, even other Esri software components outside of ArcPy, and I have come to the conclusion the real problem is in the labels themselves. Specifically, the problem lies in the use of "part" to talk about geometries. Take a look at the List of SQL functions for Esri's ST_Geometry data type, the OGC Methods on Geometry Instances for Microsoft's geometry data type, or the PostGIS Reference; you will not find a single function, method, or property with the word "part" in it. There are accessor functions for counting geometries, but they count "geometries" and not "parts." There are accessor functions for counting interior rings, but they count "interior rings" and not "parts." You see where this is going.

The problem with the ArcPy Geometry classes, at least one of them, is that Esri replaced multiple, specific geometry components with a single generic one, the "part." By abstracting geometries and rings with parts, not only did they deviate from geospatial standards and norms, they created the sideshow-worthy multi-part single-part polygon.

VinceAngelo

All geometry objects are ingested from Well-Known Text using the SgShape geometry library, which has a default "Left Hand Rule" storage orientation*. No matter how you incorrectly wrap the polygons, if the import succeeds, the result polygon will be native left-hand rule (with the polygon shells corrected, if necessary, so that holes follow the outer rings to which they belong, with opposite ring wrapping direction).

- V

*Not to be confused with what Google calls "Right Hand Rule" which is the same orientation, but as described with the hand over the "upward" face of the shape with the thumb pointing out, and fingers curling in the direction of outer ring rotation.

VinceAngelo

In truth, a polygon with a hole is multi-ring, but not multi-part. If the proper WKT starts with "POLYGON" not "MULTIPOLYGON", it is single part, with one or more interior rings (which is why even a single-ring polygon has two left and right parens - "(( ... ))"). The Geometry object method is poorly documented on this score.

- V

EidurEidsson

Then I suppose it is "multipart" if there exists a break in the sequence, no matter what comes after it. That might be useful for some tasks, but this meaning is quite different from what the description implies.

Thanks

XanderBakker

I kinda agree that a polygon with a hole that contains only 1 part should not be a multipart. Maybe it is implemented this way since the polygon object does not have a "hasHoles" property (or something similar). To understand how ArcGIS stores the geometry you can run something like this:

<SPAN class="keyword token">import</SPAN> arcpy

poly1 <SPAN class="operator token">=</SPAN> arcpy<SPAN class="punctuation token">.</SPAN>FromWKT<SPAN class="punctuation token">(</SPAN><SPAN class="string token">"POLYGON ((35 10, 45 45, 15 40, 10 20, 35 10), (20 30, 35 35, 30 20, 20 30))"</SPAN><SPAN class="punctuation token">)</SPAN>

<SPAN class="keyword token">print</SPAN><SPAN class="punctuation token">(</SPAN>poly1<SPAN class="punctuation token">.</SPAN>isMultipart<SPAN class="punctuation token">)</SPAN>
<SPAN class="keyword token">print</SPAN><SPAN class="punctuation token">(</SPAN>poly1<SPAN class="punctuation token">.</SPAN>partCount<SPAN class="punctuation token">)</SPAN>

cnt_part <SPAN class="operator token">=</SPAN> <SPAN class="number token">0</SPAN>
<SPAN class="keyword token">for</SPAN> part <SPAN class="keyword token">in</SPAN> poly1<SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp; cnt_part <SPAN class="operator token">+=</SPAN> <SPAN class="number token">1</SPAN>
&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">print</SPAN><SPAN class="punctuation token">(</SPAN><SPAN class="string token">"Part: {}"</SPAN><SPAN class="punctuation token">.</SPAN>format<SPAN class="punctuation token">(</SPAN>cnt_part<SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">)</SPAN>
&nbsp;&nbsp;&nbsp; cnt_pnt <SPAN class="operator token">=</SPAN> <SPAN class="number token">0</SPAN>
&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">for</SPAN> pnt <SPAN class="keyword token">in</SPAN> part<SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; cnt_pnt <SPAN class="operator token">+=</SPAN> <SPAN class="number token">1</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">print</SPAN><SPAN class="punctuation token">(</SPAN><SPAN class="string token">" - Pnt {}: {}"</SPAN><SPAN class="punctuation token">.</SPAN>format<SPAN class="punctuation token">(</SPAN>cnt_pnt<SPAN class="punctuation token">,</SPAN> pnt<SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="line-numbers-rows"><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN></SPAN>

It will yield this:

True
1
Part: 1
 - Pnt 1: 35 10 NaN NaN
 - Pnt 2: 10 20 NaN NaN
 - Pnt 3: 15 40 NaN NaN
 - Pnt 4: 45 45 NaN NaN
 - Pnt 5: 35 10 NaN NaN
 - Pnt 6: None
 - Pnt 7: 20 30 NaN NaN
 - Pnt 8: 30 20 NaN NaN
 - Pnt 9: 35 35 NaN NaN
 - Pnt 10: 20 30 NaN NaN<SPAN class="line-numbers-rows"><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN></SPAN>

As you can see Pnt 6 is None and indicates the start of a hole.

EidurEidsson

Outer–inner: CCW–CW, CCW–CCW, CW–CW, CW–CCW, all same result.

The WKT is first converted to an arcpy geometry object, which I don't know how is structured exactly. If they are printed as WKT they all become CCW–CW multipolgygons. What I can read from the documentation is that isMultipart should agree with partCount.

DanPatterson_Retired

it is a multipart and the count is 1. one point ring is clockwise, the other is clockwise, hence the hole

To experiment, repeat the experiment with both point rings oriented in a clockwise order

Nimm an der Unterhaltung teil

Angemeldete Mitglieder können Beiträge verfassen, Updates folgen und mehr. Neu hier? Registriere ein kostenloses Konto.

Schnellzugriffe

Community Help
Find useful guides, FAQs, and documents to help you navigate and make the most of Esri Community.