[Qgis-developer] Postgresql provider - Use ST_RemoveRepeatedPoints for server-side simplification

[kimaidou]

Hi all,

The PR has been merged by Matthias Kuhn. You could now test it directly in
last master.

Regards,
Michaël

2015-12-01 16:17 GMT+01:00 kimaidou <kimaidou at gmail.com>:

> oups, gmail got rid of the table... Here is a human readable version
>
> Method used --> vertex number
>
> "geom" --> 3 763 284 |
> st_snaptogrid( "geom", 407.618 ) --> 1 220 892
> st_removerepeatedpoints( "geom", 407.618 ) --> 689 300
> st_simplify( st_removerepeatedpoints( "geom", 407.618 ), 356.665, true )
> --> 303 292
>
>
> 2015-12-01 16:15 GMT+01:00 kimaidou <kimaidou at gmail.com>:
>
>> Hi,
>>
>> New PR update with addition of missing SIP bindings and use of
>> ST_Simplify with third parameter "True" to decrease the size of data to
>> download by QGIS.
>> Please help to test with various data and report.
>>
>> Some quick results, with the same data and query as mentioned in the PR,
>> to show how the number of vertexes decreases. It would lead to best
>> performance also because the data will be downloaded from the PostGIS faster
>> query number of vertexes "geom" 3 763 284 st_snaptogrid( "geom", 407.618
>> ) 1 220 892 st_removerepeatedpoints( "geom", 407.618 ) 689 300 st_simplify(
>> st_removerepeatedpoints( "geom", 407.618 ), 356.665, true ) 303 292
>>
>> Of course, this is done when viewing the whole layer (zoom to layer
>> extent). For big scales, this PR will not improve so drastically the
>> situation compared to the previous use if ST_SnapToGrid
>>
>> Should we not accept the PR so that many more users can try it with
>> master branch ?
>>
>> Cheers
>> Michaël
>>
>> 2015-11-27 14:27 GMT+01:00 kimaidou <kimaidou at gmail.com>:
>>
>>> Hi all,
>>>
>>> I updated my PR.
>>> I made some quick tests, and it seems this PR can improve speed for
>>> PostGIS layers ( with PostGIS 2.2 )
>>> More details in the last comment [1]
>>>
>>> Please help to test it with a variety of data types and complexity.
>>>
>>> [1] https://github.com/qgis/QGIS/pull/2410#issuecomment-160138487
>>>
>>> Regards
>>> Michaël aka "kimaidou"
>>>
>>> 2015-10-30 11:50 GMT+01:00 kimaidou <kimaidou at gmail.com>:
>>>
>>>> Hi all
>>>>
>>>> Following the blog post written by Paul Ramsey [1], I decided to
>>>> propose using PostGIS 2.2 ST_RemoveRepeatedPoints function instead of
>>>> ST_SnapToGrid to do the server side simplification
>>>>
>>>> We could also investigate other new features, such as the 3rd parameter
>>>> for ST_Simplify, but we use St_SimplifyPreserveTopology in QGIS, and I do
>>>> not think this function has got this new parameter too.
>>>>
>>>> I made a pull request : see [2]
>>>> Please help me to test and review it
>>>>
>>>> [1] http://blog.cartodb.com/smaller-faster/
>>>> [2] https://github.com/qgis/QGIS/pull/2410
>>>>
>>>
>>>
>>
>
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