[postgis-users] ST_Intersection does not preserve M value

[Bo Guo]

FME, which sources from GEOS 
(https://cdn.safe.com/resources/fme/FMEDesktop_Legal_Notices_2019.0.pdf), 
did not handle the measurement with its Clipper transformer until about 
two years ago.  Wonder if they achieved this through direct update the 
GEOS lib or through post-GEOS enhancement.

On 5/6/19 2:53 PM, Martin Davis wrote:
> Not exactly the same thing - I believe that ticket is referring to 
> just the WKB format handling?
>
> I can make a ticket for measure handling by the overlay operations if 
> there isn't one already.
>
> On Mon, May 6, 2019 at 11:31 AM Darafei "Komяpa" Praliaskouski 
> <me at komzpa.net <mailto:me at komzpa.net>> wrote:
>
>     It's in backlog for 6 years already I believe:
>     https://trac.osgeo.org/geos/ticket/466
>
>     пн, 6 мая 2019, 19:33 карыстальнік Martin Davis
>     <mtnclimb at gmail.com <mailto:mtnclimb at gmail.com>> напісаў:
>
>         It should be possible to post-process GEOS results to
>         re-populate the M values if present.  Linear interpolation
>         could be used to estimate values at intra-segment points.  We
>         can put this on the list for future development.
>
>         On Mon, May 6, 2019 at 4:48 AM Darafei "Komяpa" Praliaskouski
>         <me at komzpa.net <mailto:me at komzpa.net>> wrote:
>
>             Hi,
>
>             GEOS operations do not preserve M, but sometimes preserve
>             Z. You can try
>             ST_SwapOrdinates(ST_Intersection(ST_SwapOrdinates(geom,
>             'zm'),...), 'zm').
>
>             On Thu, May 2, 2019 at 5:19 AM Bo Guo
>             <bo.guo at gisticinc.com <mailto:bo.guo at gisticinc.com>> wrote:
>
>                 Hi there,
>
>                 I was trying to cut a portion of the LRS route with an
>                 area using
>                 ST_Intersection.  However the resulting route no
>                 longer carries measure
>                 value.  The behavior is the same for version 9.6 or
>                 the latest version
>                 11.  Anyone has any suggestions?
>
>                 Thanks!
>
>                 Bo
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>
>             -- 
>             Darafei Praliaskouski
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-- 
Bo Guo, PhD, PE
Gistic Research, Inc.
2033 E Warner Rd. Ste 105
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Tel: 480-656-9962
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