[mapserver-dev] Thin polygon issue...

[Tamas Szekeres]

Hi Steve,

I've tested your fix and it could indeed solve the problem we have
encountered. Should I apply the fix in MapServer or you are willing to do
that?

Thanks,

Tamas


2015-12-30 0:04 GMT+01:00 Lime, Steve D (MNIT) <Steve.Lime at state.mn.us>:

> In case anyone is interested in before/after images, I’ve included samples
> based on data from Tamas:
>
>
>
> -          test-before.png used git/master
>
> -          test-after.png used git/master but with the lines referenced
> below uncommented
>
> -          test-ignore-edge-distance.png used git/master but uses a
> processing option to skip the label point edge distance computation
>
>
>
> Steve
>
>
>
> *From:* mapserver-dev [mailto:mapserver-dev-bounces at lists.osgeo.org] *On
> Behalf Of *Lime, Steve D (MNIT)
> *Sent:* Thursday, December 24, 2015 11:35 AM
> *To:* Tamas Szekeres <szekerest at gmail.com>
> *Cc:* mapserver-dev at lists.osgeo.org
> *Subject:* [mapserver-dev] Thin polygon issue...
>
>
>
> Hi Tamas: Quiet around here the day before xmas so I got time to look into
> this issue. I think I’ve found the problem in mapprimitive.c, the function
> msPolygonLabelPoint() look for two lines:
>
>
>
>   /* lp->y = y; */
>
>   /* lp->x = x; */
>
>
>
> I’m really not sure why they were commented out but that’s the source of
> the issue. Try uncommenting them and drawing the data that were giving you
> the issue. It cleared things up for me using your test data. That’s not to
> say that being able to bypass the distance computation isn’t a good idea.
> That could be done as a processing option. I don’t think it’s worth being
> able to set the initial label point computation method (center of gravity
> vs bbox vs centroid) is worth it.
>
>
>
> The next question would be where to apply this fix, it’s definitely a bug.
> It will change label position in instances where the fallback scanline
> method is used: 1) where points are too close to the edge of a polygon or
> 2) where the initial label point computation produces a point outside the
> polygon. That could break regression tests if we have any that trigger the
> scanline method. I wouldn’t think this would cause issues with tile caches.
>
>
>
> I would propose patching 6.4, 7.0 and master and adding the distance
> bypass to master.
>
>
>
> Steve
>
>
>
>
>
>
>
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