[postgis-tickets] [PostGIS] #2232: Accumulated error with relative coordinates in ST_AsSvg

[PostGIS]

#2232: Accumulated error with relative coordinates in ST_AsSvg
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 Reporter:  nicklas  |       Owner:  nicklas 
     Type:  defect   |      Status:  assigned
 Priority:  medium   |   Milestone:          
Component:  postgis  |     Version:  2.0.x   
 Keywords:           |  
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Description changed by nicklas:

Old description:

> When using ST_ASSvg outputting relative rounded coordinates you might get
> accumulated rounding errors.
>
> I saw huge errors like that when testing twkb on polygons with thousands
> of vertex-points.
>
> Example:
>

>
> {{{
> select
> st_assvg('LINESTRING(0 0, 0.4 0, 0.8 0, 1.2 0,1.6 0, 2 0)'::geometry,1,0)
> }}}
>
> returns:
>
> {{{
> M 0 0 l 0 0 0 0 0 0 0 0 0 0
> }}}
>
> I fixed it in twkb-case in the spike with #11165, probably the same
> approach can be used here.
>
> Just not get the relative value as relative to the previous coordinate,
> but relative to the accumulates relative coordinates achieved.

New description:

 When using ST_ASSvg outputting relative rounded coordinates you might get
 accumulated rounding errors.

 I saw huge errors like that when testing twkb on polygons with thousands
 of vertex-points.

 Example:



 {{{
 select
 st_assvg('LINESTRING(0 0, 0.4 0, 0.8 0, 1.2 0,1.6 0, 2 0)'::geometry,1,0)
 }}}

 returns:

 {{{
 M 0 0 l 0 0 0 0 0 0 0 0 0 0
 }}}

 I fixed it in twkb-case in the spike with r11165, probably the same
 approach can be used here.

 Just not get the relative value as relative to the previous coordinate,
 but relative to the accumulates relative coordinates achieved.

--

-- 
Ticket URL: <http://trac.osgeo.org/postgis/ticket/2232#comment:2>
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