WKT Standard – Where to Find Well-Known Text References and Specifications

standardswell-known-text

I had a little confusion about the representation of a geometry as well-known-text (WKT). I was searching for the WKT Specs to search for the exact representation, but I did not find the Standard. Is there a standards document or reference for WKT? where can I find it?

Best Answer

Well known text for geometry is defined in OGC 01-103r4 (amongst other places). Section 7 of that document provides the syntax. There is also a list of SQL functions relating to those in Part 2 of the Simple Features spec (also an OGC product).

The ISO documents are just a more expensive way to get much the same thing.

There are useful extensions such as the Extended WKT (EWKT) that is defined by PostGIS and supported by various other tools such as SpatiaLite, and provides the SRS, which you probably want.

Update: As pointed out in a comment, there is also WKT representation for Coordinate Reference Systems: OGC 18-010r7. However these two WKT forms are using similar syntax to describe different things - one is for a geometry (e.g. a linestring), and the other for a CRS (e.g. for a geometric or temporal datum).

Related Solutions

ArcObjects – Converting Between Esri Geometry and WKT

Using the IWkb interface does a nice job at converting between an IGeometry and WKB. From a WKB you can use the Microsoft.SqlServer.Types library to convert a WKB to SqlGeometry then back to WKT.

IWkb wkb = geometry as (IWkb); //(Where geometry is an instance of IGeometry)
byte[] wkb_bytes = new byte[wkb.WkbSize];
int byte_count = wkb.WkbSize;
wkb.ExportToWkb(ref byte_count, out wkb_bytes[0]);

At this point you have the WKB stored in wkb_bytes. If you want to go the next step to SqlGeometry then to WKT:

SqlGeometry sqlGeom = SqlGeometry.STGeomFromWKB(new SqlBytes(wkb_bytes), srid);
string wkt = sqlGeom.ToString();

ArcPy WKT Conversion – Converting Geometry to WKT Using ArcPy

A da.searchcursor should work for you.

for row in arcpy.da.SearchCursor("path2data", ["SHAPE@WKT"]):
  print row[0]

POINT Z (-119.53753379999995 49.854383300000052 303.14500000000407)

doc here: http://resources.arcgis.com/en/help/main/10.1/index.html#//002z0000001t000000

Note: SHAPE@JSON, SHAPE@WKB, and SHAPE@WKT tokens were made available at ArcGIS 10.1 Service Pack 1.

Or, if you're after the samples toolbox like you mentioned - its there, just deprecated. You can call into it with scripts still. If you need the actual toolbox you can use, its here on the old Model and Script Gallery

EDIT (extra example)...Because you asked so nicely: :)

for row in arcpy.da.SearchCursor("GPX_Layer", ["SHAPE@WKT"],where_clause="TYPE = 'a'"):
    print row[0]

It's just the same as a "select by attributes" type of query/expression. I have a field called "TYPE" and and a value 'a'.

Best Answer

Related Solutions

ArcObjects – Converting Between Esri Geometry and WKT

ArcPy WKT Conversion – Converting Geometry to WKT Using ArcPy

Related Question