topic Re: Create NIL (zero vertex) geometry in Geodatabase Questions

Create NIL (zero vertex) geometry

Bud — Tue, 21 Nov 2023 14:36:20 GMT

In a separate post (ST_Geometry — Don't allow empty geometry), @VinceAngelo mentioned:

A NIL (zero vertex) geometry is a valid shape type. It is required for some operations (e.g., the result of the intersection of two disjoint features). The shapefile specification permits Nil paired with any other one geometry type as the supported types in shapefiles.

Are there any other ways to create NIL (zero vertex) geometry -- other than "intersecting two disjoint features"?

For example, create NIL (zero vertex) geometry using editing tools in ArcGIS Pro. Use case: SQL query testing (Oracle 18c; 10.7.1 EGDB; SDE.ST_GEOMETRY).

Thanks.

Re: Create NIL (zero vertex) geometry

DanPatterson — Mon, 30 Oct 2023 17:45:18 GMT

pline = arcpy.Polyline(arcpy.Array(None)) # -- create a polyline with an empty array # -- some properties pline.length # -- no length 0.0 pline.pointCount # -- no points 0 pline.JSON # -- no path to make '{"paths":[],"spatialReference":{"wkid":null}}' print(pline.centroid) # -- it has no centroid None

Re: Create NIL (zero vertex) geometry

VinceAngelo — Tue, 31 Oct 2023 00:51:47 GMT

You can use the Well-Known Text keyword "EMPTY" to generate a NIL geometry:

import arcpy sr = arcpy.SpatialReference(4326) np = arcpy.FromWKT("POLYGON EMPTY",sr) print("np - pointCount: {:d} JSON: {:s}".format(np.pointCount,np.JSON)) nl = arcpy.FromWKT("LINESTRING EMPTY",sr) print("nl - pointCount: {:d} JSON: {:s}".format(nl.pointCount,nl.JSON)) nm = arcpy.FromWKT("MULTIPOINT EMPTY",sr) print("nm - pointCount: {:d} JSON: {:s}".format(nm.pointCount,nm.JSON)) nx = arcpy.FromWKT("POINT EMPTY",sr) print("nx - pointCount: {:d} JSON: {:s}".format(nx.pointCount,nx.JSON)) print("nx - firstPoint: {:s}".format(str(nx.firstPoint)))

which results in:

np - pointCount: 0 JSON: {"rings":[],"spatialReference":{"wkid":4326,"latestWkid":4326}} nl - pointCount: 0 JSON: {"paths":[],"spatialReference":{"wkid":4326,"latestWkid":4326}} nm - pointCount: 0 JSON: {"points":[],"spatialReference":{"wkid":4326,"latestWkid":4326}} nx - pointCount: 1 JSON: {"x":"NaN","y":"NaN","spatialReference":{"wkid":4326,"latestWkid":4326}} nx - firstPoint: None

Curiously, the PointGeometry type always returns a pointCount of one, but the firstPoint is None.

WKT can also be used at the SQL prompt in Oracle:

SQL> SELECT 'POLYGON' as type,SDE.ST_ASTEXT(SDE.ST_PolyFromText('POLYGON EMPTY',4326)) as geom FROM DUAL; TYPE ------- GEOM -------------------------------------------------------------------------------- POLYGON POLYGON EMPTY SQL> SELECT 'LINE ' as type,SDE.ST_ASTEXT(SDE.ST_LineFromText('LINESTRING EMPTY',4326)) as geom FROM DUAL; TYPE ------- GEOM -------------------------------------------------------------------------------- LINE LINESTRING EMPTY SQL> SELECT 'MPOINT ' as type,SDE.ST_ASTEXT(SDE.ST_MPointFromText('MULTIPOINT EMPTY',4326)) as geom FROM DUAL; TYPE -------- GEOM -------------------------------------------------------------------------------- MPOINT MULTIPOINT EMPTY SQL> SELECT 'POINT ' as type,SDE.ST_ASTEXT(SDE.ST_PointFromText('POINT EMPTY',4326)) as geom FROM DUAL; TYPE ------- GEOM -------------------------------------------------------------------------------- POINT POINT EMPTY SQL>

- V

Re: Create NIL (zero vertex) geometry

VinceAngelo — Tue, 31 Oct 2023 00:58:35 GMT

For reference, the empty array trick works for Polygon, Polyline, and Multipoint classes, but PointGeometry won't accept a None point parameter.

- V

Re: Create NIL (zero vertex) geometry

DanPatterson — Tue, 31 Oct 2023 02:09:33 GMT

Which brings us back to the old question about arcpy.Point having a value for x and y which is a valid number.

You can assign math.nan or numpy.nan to the x and y values but you have to test whether they are nan (not a number)

I can only wish points could just be defined from arrays

np.full(shape=(4,), fill_value=np.nan, order='C') array([nan, nan, nan, nan]) # -- or np.empty((0,)) array([], dtype=float64)

import math import arcpy p0 = arcpy.Point() # -- sadly given default values p0 <Point (0.0, 0.0, #, #)> # -- define invalid x, y values p1 = arcpy.Point(math.nan, math.nan) p1 <Point (nan, nan, #, #)> # # -- then check in code math.isnan(p1.X) pg0 = arcpy.PointGeometry(p0, None, None, None) pg0[0] # must contain a point <Point (nan, nan, #, #)>

Re: Create NIL (zero vertex) geometry

Bud — Mon, 13 Nov 2023 16:57:11 GMT

Idea: Create Nil geometry using editing tools

Re: Create NIL (zero vertex) geometry

Bud — Mon, 20 Nov 2023 20:36:11 GMT

I'm struggling with Python since I don't write Python scripts very often. Is there any chance you could provide a full script for inserting a nil geometry row into an existing polygon feature class?

Re: Create NIL (zero vertex) geometry

Bud — Tue, 21 Nov 2023 20:17:45 GMT

For my notes, regarding, "WKT can also be used at the SQL prompt in Oracle:"

In Oracle, functions like SDE.ST_PolyFromText() return the subtype [SDE.ST_POLYFROMTEXT] , not the supertype [SDE.ST_GEOMETRY] .

See: Is it ok to store ST_POLYFROMTEXT in ST_GEOMETRY shape column?

I suspect that might be a problem: Esri Canada Case #03491474 - Is it ok to store ST_POLYFROMTEXT in ST_GEOMETRY shape column?

This bug report suggests to "...convert any geometry values which were created with a subtype to st_geometry, by using the st_geometry constructor."

Bug: Unable to define a query layer in ArcGIS where the data source uses an st_geometry subtype in Oracle

That seems to work:

For what it's worth, I think "by using the st_geometry constructor." is a recent addition to that bug report. That part wasn't included in the bug report previously; Esri must have added it to clarify how to convert from the subtype to the supertype.

GIS Stack Exchange: Get ArcGIS to recognize ST_POINT

Ideas: