[postgis-devel] KNN and 9.5

Tue Jan 5 20:54:25 PST 2016

(you can get the natural_earth2 data set from the OSGeo Live -- its one 
of the main sample databases)
  --Brian

On Tue, 5 Jan 2016 23:04:32 -0500, Paragon Corporation  wrote:

       Gives me a 404. 

Thanks,

Regina

From: postgis-devel [mailto:postgis-devel-bounces at lists.osgeo.org] On 
Behalf Of Stephen Mather
Sent: Tuesday, January 05, 2016 10:31 PM
To: PostGIS Development Discussion

Subject: Re: [postgis-devel] KNN and 9.5

Hi Regina,

The dataset is from Natural 
Earth: http://www.naturalearthdata.com/http//www.naturalearthdata.com/download/10m/physical/ne_10m_geography_regions_polys.zip

I imported that dataset and transformed to 3857 just to get it in 
planar coordinates. I affectionately called it regions_polys_subset. 

https://gist.github.com/smathermather/320273309124bf8b80a7

But honestly, as long as you throw the knn in a function, any point 
dataset will do it, I think. 

Hope this helps (and helps in time!)!

Cheers,

Best,

Steve

On Sun, Jan 3, 2016 at 9:24 PM, Paragon Corporation  wrote:

       Steve,

Well that sucks.  Can I borrow your dataset to test with?

Thanks,

Regina

From: postgis-devel [mailto:postgis-devel-bounces at lists.osgeo.org] On 
Behalf Of Stephen Mather
Sent: Sunday, January 03, 2016 10:41 AM
To: PostGIS Development Discussion

Subject: Re: [postgis-devel] KNN and 9.5

Hi Regina,

On a lark, I also tested with 2.3.0dev r14538 (9.5rc1)

"POSTGIS="2.3.0dev r14538" GEOS="3.5.0-CAPI-1.9.0 r4084" SFCGAL="1.2.2" 
PROJ="Rel. 4.8.0, 6 March 2012" GDAL="GDAL 1.10.1, released 2013/08/26" 
LIBXML="2.9.1" LIBJSON="0.11.99" RASTER"

Same result. 

Cheers,

Best,

Steve

On Sun, Jan 3, 2016 at 9:34 AM, Stephen Mather  wrote:

       2.2.0 and RC1. Should I be trying 2.2 branch?

SELECT version();

"PostgreSQL 9.5rc1 on x86_64-pc-linux-gnu, compiled by gcc (Debian 
4.7.2-5) 4.7.2, 64-bit"

SELECT postgis_full_version();

"POSTGIS="2.2.0 r14208" GEOS="3.5.0-CAPI-1.9.0 r4084" SFCGAL="1.2.2" 
PROJ="Rel. 4.8.0, 6 March 2012" GDAL="GDAL 1.10.1, released 2013/08/26" 
LIBXML="2.9.1" LIBJSON="0.11.99" RASTER"

On Sun, Jan 3, 2016 at 2:18 AM, Paragon Corporation  wrote:

       Steve,

Haven't had a chance to look thru what you have here and test it out myself. 

The issue I flagged in the ticket was fixed in PostgreSQL 9.5 code base 
upstream:

http://www.postgresql.org/message-id/55630D9D.3090508@iki.fi

It's my understanding that you should never get that notice again.  So 
I'm a bit concerned you are.  It's possible you found another area 
where this issue arises and is not handled. 

Are you running PostgreSQL 9.5RC1 and latest PostGIS 2.2 branch (or 2.2.0?). 

Thanks,

Regina

From: postgis-devel [mailto:postgis-devel-bounces at lists.osgeo.org] On 
Behalf Of Stephen Mather
Sent: Sunday, January 03, 2016 1:56 AM
To: PostGIS Development Discussion

Subject: [postgis-devel] KNN and 9.5

Hi All,

Short version:

Does Regina's comment on http://trac.osgeo.org/postgis/ticket/2703 
regarding ERROR: index returned tuples in wrong order apply to any 
uses of indices in conjunction with KNN?

Long version:

Digging many of the 2.2 / 9.5 updates. Having fun on break playing with 
skeleton simplification and using KNN in the process. Yes. For those of 
you who know me, this is an obsession that won't die quietly. 

https://smathermather.files.wordpress.com/2016/01/screen-shot-2016-01-03-at-1-19-26-am.png

I've got a function that does my KNN in the usual style, finds the 
nearest 2 points, and makes a line from them:

CREATE OR REPLACE FUNCTION zz_knn_wonderful_points (geometry) RETURNS 
geometry AS $$

-- Here are my wonderful points to KNN search:

WITH index_query AS (

            SELECT edge.geom AS geom

            FROM (SELECT * FROM regions_dpoints WHERE gid = 882) AS edge

-- This is my query point

            ORDER BY $1

            edge.geom LIMIT 2

            )

SELECT ST_MakeLine(geom) FROM index_query

$$ LANGUAGE SQL;

The intent is to implement angle values as an importance criterion for 
simplifying the skeleton as described at minute 2:20 in Balint Miklos 
video on the scale axis 
transform: http://balintmiklos.com/scale-axis/The_Scale_Axis_Picture_Show.mp4

Actually, in the final function, I will likely directly calculate the 
angle and return that instead of the geometry, but I digress. 

Regardless, when I use this function as is, it works great in drawing 
lines connecting the two nearest points to the vertex in the medial 
axis:

DROP TABLE IF EXISTS test CASCADE;

CREATE TABLE test AS

WITH returnline AS (

            SELECT oid, gid,

                        ST_Union(

                        ST_MakeLine( 
ST_StartPoint(zz_knn_wonderful_points(subset.geom)), subset.geom),

                        ST_MakeLine( 
ST_EndPoint(zz_knn_wonderful_points(subset.geom)), subset.geom)

                        )

                        AS geom FROM

                        (SELECT * FROM regions_points WHERE oid = 882) subset

)

SELECT * FROM returnline

;

However, as implemented, this will not work in the case of overlapping 
geometries, such as Natural Earth's label polygon dataset 
"ne_10m_geography_regions_polys":

https://smathermather.files.wordpress.com/2016/01/screen-shot-2016-01-03-at-1-33-01-am.png

And so I add a constraint using an integer ID:

CREATE OR REPLACE FUNCTION zz_knn(integer,geometry) RETURNS geometry AS $$

-- Here are my wonderful points to KNN search:

WITH index_query AS (

            SELECT edge.geom AS geom

            FROM (SELECT * FROM regions_dpoints WHERE gid = $1) AS edge

-- This is my query point

            ORDER BY $2

            edge.geom LIMIT 2

            )

SELECT ST_MakeLine(geom) FROM index_query

$$ LANGUAGE SQL;

And now it takes much longer and fails with 

"

ERROR:  index returned tuples in wrong order

CONTEXT:  SQL function "zz_knn" statement 1

********** Error **********

ERROR: index returned tuples in wrong order

SQL state: XX000

Context: SQL function "zz_knn" statement 1

"

Thanks!

Cheers,

Best,

Steve Mather

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--
Brian M Hamlin
OSGeo California Chapter
blog.light42.com

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