gmane.comp.gis.postgis

How to smoothify (rounding the edges)?

tee — 2012-05-25T23:19:02

Dear list,

I am trying smoothify some linestring.
ST_OffsetCurve looks good, but simply simulates just one side of a
ST_Buffer. 
Chaining of ST_OffsetCurve could be the right way.

SELECT
ST_OffsetCurve(
ST_OffsetCurve(
ST_OffsetCurve(
ST_GeometryFromText(
'LINESTRING(
369172.556 5645414.822
,369083.213632107 5645360.17950829
,369074.985 5645382.472
,368991.798 5645340.312
,368948.814 5645362.793
,368922.301 5645286.628
,368868.668 5645301.318
,368762.112 5645217.804
,368722.516936163 5645220.71672624
,368734.299541879 5645251.65724707
,368696.988917574 5645268.59693863
,368652.612373605 5645243.03860572
,368655.33980816 5645277.83126126
,368622.411 5645234.496)'
,25832)
,-5
,'quad_segs=4 join=round')
,10
,'quad_segs=4 join=round')
,-5
,'quad_segs=4 join=round');

http://postgis.17.n6.nabble.com/file/n4997829/smoothify.png 

How can I get my data edgeless.

Thanks a lot and best regards,

Re: Topology: Simplifying Coastlines with Islands

Sandro Santilli — 2012-05-25T21:20:28

...

Yeah, it might work at 0.25 :)


I considered it generally about error messages. The first one above,
for example, might be more useful if it told you _which_ edge was
the simplified edge crossing, and maybe even _where_...


--strk;

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Re: Topology: Simplifying Coastlines with Islands

Michiel J. van Heek — 2012-05-25T21:15:09

Hello Sandro,

Thank you for your reply.

These are the warnings for edge 11652, the coastline of Norway (on the  
screenshot in my previous post):

WARNING:  Simplification of edge 11652 with tolerance 0.5 failed:  
SQL/MM Spatial exception - geometry crosses an edge
WARNING:  Simplification of edge 11652 with tolerance 0.25 failed:  
SQL/MM Spatial exception - curve not simple
WARNING:  Simplification of edge 11652 with tolerance 0.125 failed:  
SQL/MM Spatial exception - curve not simple
WARNING:  Simplification of edge 11652 with tolerance 0.0625 failed:  
SQL/MM Spatial exception - curve not simple
WARNING:  Simplification of edge 11652 with tolerance 0.03125 failed:  
SQL/MM Spatial exception - curve not simple
WARNING:  Simplification of edge 11652 with tolerance 0.015625 failed:  
SQL/MM Spatial exception - curve not simple
WARNING:  Simplification of edge 11652 with tolerance 0.0078125  
failed: SQL/MM Spatial exception - curve not simple

The "curve not simple" makes we want to try your suggestion

Re: Topology: Simplifying Coastlines with Islands

Sandro Santilli — 2012-05-25T20:28:59

I think you should figure out more about why the simplification
fails. The function in the post raises a WARNING on each failure,
what does that warning say ? I'm asking because there's also the
case of self-topology breakage, which could be prevented by using
ST_SimplifyPreserveTopology rather than ST_Simplify. 

If your assumption about why simplification fails is correct you
could make things better by splitting the complex edge near the
islands (see ST_ModEdgeSplit).


The function in the post is still only considering each edge in
turn and has no knowledge of which faces are defined by those
edges, let alone which faces define your feature (mainland, island).
You'll need something more sofisticated for that, and I'm not sure
there's an easy general handling for such cases. I mean, there could
still be the case in which simplifying an edge would intersect an
island which doesn't belong to the same feature...

Let me know what you found when looking closer at the failure messages.
There's a ticket to mak

Re: Nearest neighbor in 3D

Paul Ramsey — 2012-05-25T19:37:04

Using ST_3DDistance will work and give you the right answer, but it
will not be index assisted. The KNN operator <-> is only implemented
against the 2D index currently.

Paul

On Fri, May 25, 2012 at 5:15 PM, Bartosz Bekier
<bartosz.bekier< at >gmail.com> wrote:

Re: ST_Aspect artifacts?

David B�langer — 2012-05-25T17:29:50

Hi,

May be you can use gdal_dem with PostGis Raster reader (mode 2) if you want create derived product from DEM?  http://www.gdal.org/gdaldem.html



It is working very well with gdal 1.8. Moreover you can extrapolate  values along the borders of the tiles.


If you  just want merging adjacent rasters you can use gdal_translate with PostGis Raster reader (mode 2).


David

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Re: Error browsing database

Paolo Cavallini — 2012-05-25T17:17:40

Il 25/05/2012 18:39, Bborie Park ha scritto:
sure you should. comments, tickets, fixes and improvements welcome:
http://hub.qgis.org/projects/dbmanager/
all the best.

Re: ST_Aspect artifacts?

Paolo Cavallini — 2012-05-25T17:08:23

Il 25/05/2012 19:02, Pierre Racine ha scritto:
ok. again, thanks for clarifying.
all the best.

Re: ST_Aspect artifacts?

Pierre Racine — 2012-05-25T17:02:36

Yeah. ST_Union is good for unioning overlapping rasters (e.g. computing the mean of a temperature series) but not for merging adjacent rasters. We will have to write something else for that.

Pierre

Re: ST_Aspect artifacts?

Paolo Cavallini — 2012-05-25T16:52:41

Il 25/05/2012 18:29, Pierre Racine ha scritto:
I imagined, thanks. So I tried to merge the rasters with ST_Union, but I
had to stop after ~2h with pg< at >100% CPU (a small raster, 1300 tiles 64x64).
Urgh!
All the best.

Re: Error browsing database

Bborie Park — 2012-05-25T16:39:50

Really?!  I'll have to try that out.

Topology: Simplifying Coastlines with Islands

Michiel J. van Heek — 2012-05-25T16:36:39

Dear list,

I am trying to simplify a dataset of country boundaries by using  
topology functions, as described in Strk's Blog:  
http://strk.keybit.net/blog/2012/04/13/simplifying-a-map-layer-using-postgis-topology/

This has worked quite well, except for coastlines with islands nearby.  
The simplified coastline would probably intersect the island, or pass  
the island at the wrong side, leading to invalid topology. Does that  
mean that countries with coastal islands such as Canada and Norway  
(see attached image) cannot be simplified this way?

Ideally, islands in the way of a to-be-simplified coastline should be  
merged with the mainland. (I have already removed the smaller islands,  
but I think I should not remove the bigger islands too.)

Best regards,
Michiel.

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Re: ST_Aspect artifacts?

Pierre Racine — 2012-05-25T16:29:51

Not yet...

Re: Error browsing database

Paolo Cavallini — 2012-05-25T15:57:47

Il 25/05/2012 17:32, Bborie Park ha scritto:
you better believe it ;)
Faunalia (Giuseppe Sucameli) is the maintainer of it.
All the best.

Re: Error browsing database

Bborie Park — 2012-05-25T15:32:52

I don't believe the DB Manager in QGIS works for PostGIS Raster.
There is a PostGIS Raster plugin available though.  I think it is
available in the plugin manager...

-bborie

Nearest neighbor in 3D

Bartosz Bekier — 2012-05-25T15:15:07

Hello All!

This is my first post on the PostGIS mailing list:-).

I would like to use the <-> to solve the nearest neighbor problem, but in
3D space. I tried to do this in 2D and it works perfectly, but apparently
it doesn't cover the 3D case.

Basically I have a table of 3D points (x, y, z) and would like to do:

    ORDER BY point <-> POINT(0 0 0)

but the distance taken into account should be 3D Euclidean distance. Do I
have to use ST_3DDistance() for it or is there a faster way?

Thanks in advance!

Regards,

ST_Aspect artifacts?

Paolo Cavallini — 2012-05-25T12:56:47

Hi all.
The raster resulting from:
CREATE TABLE aspect as select rid, ST_aspect(rast,1,'8BUI') as rast from
hdr;
does not calculate correctly values along the borders of the tiles.
Any way to avoid this?
All the best.

Re: Difference between ST_Union and ST_Collect

Luca Morandini — 2012-05-25T10:43:14

Crystal clear :)

Regards,

Luca Morandini
Data Architect - AURIN project
Department of Computing and Information Systems
University of Melbourne

Re: Difference between ST_Union and ST_Collect

Sandro Santilli — 2012-05-25T10:41:31


ST_BuildArea expects input to be correctly noded. Failing that, the
actual result is undefined. Passing the input trough ST_Union is a trick
to obtain proper noding.

--strk;

  ,------o-. 
  |   __/  |    Delivering high quality PostGIS 2.0 !
  |  / 2.0 |    http://strk.keybit.net - http://vizzuality.com
  `-o------'

Re: Difference between ST_Union and ST_Collect

Luca Morandini — 2012-05-25T10:38:44

Of course, but it has a different behaviour when it is given a collection of lines 
(some intersecting) or a single geometry... on the other hand, it may be ST_Union 
that resolves the "loops" before sending the geometry to ST_BuildArea).



The issue has been solved by using ST_Union, but I still can't fathom why entire 
polygons were dropped by ST_BuildArea when their boundaries intersected..

Regards,

Luca Morandini
Data Architect - AURIN project
Department of Computing and Information Systems
University of Melbourne

Re: Difference between ST_Union and ST_Collect

Sandro Santilli — 2012-05-25T10:30:46

BuildArea is not an aggregate so won't "internally" collect the inputs. 
I'm not sure this solves your problem.

--strk; 

  ,------o-. 
  |   __/  |    Delivering high quality PostGIS 2.0 !
  |  / 2.0 |    http://strk.keybit.net - http://vizzuality.com
  `-o------'