[mapserver-dev] Label Angle Auto Issue (Trac #1688)

[Stephen Woodbridge]

Chris,

Yeah, that is a looong ticket with a lot of discussion.

I'm +1 with moving this forward. I think Steve L suggestions of making 
the MS_AUTO, MS_AUTO2, etc values that are not typical angle values 
(like 99990, 99991, ...) or adding an new ANGLEMODE keyword to the 
mapfile should work nicely.

-Steve W


Chris Hodgson wrote:
> Hi Devs,
> 
> The issue is Trac #1688 [1] - it's kinda long, so in summary: we want a 
> way to be able to force labels to be drawn upside down, based on the 
> angle of the line. The existing "ANGLE AUTO" function is "smart" and 
> always tries to render them right-side up, but in our client's case the 
> line segments have been specifically made to define the location of 
> individual characters for labeling actual map features, and if the 
> segment goes from right-to-left it intends for the character to be 
> rendered upside down (manually defining the placement of characters for 
> a result that looks something like "ANGLE FOLLOW").
> 
> I believe this issue has been hanging around (for 4 years) because 
> no-one has tried hard enough force a consensus on how to implement the 
> configuration of this feature - that's why I'm bringing it out of Trac 
> and onto the dev list, my apologies if this is not appropriate.
> 
> Dan suggested the following a couple years back:
> 
> Here is an idea: instead of adding a new autoanglealgorithm member in 
> the labelObj as was proposed in the auto2.tar.gz patch, we could get rid 
> of autoangle and autofollow and combine all of them into a single 
> label->anglemode member with the following possible values:
> 
> - 0, the default means that the angle value is either static or bound to 
> an attribute
> - MS_AUTO
> - MS_AUTO2 (the new algorithm)
> - MS_FOLLOW
> 
> Steve, do you expect any problem with that approach? I can take this 
> ticket if you want, just reassign to me.
> 
> Steve replied with:
> 
> Dan, I think that would work. MapScript would be simplified 
> ($label->anglemode = ...) and I assume we'd keep the mapfile syntax the 
> same (e.g. ANGLE AUTO2). We could allow explictly setting the anglemode 
> in the mapfile as well with the idea of depricating ANGLE AUTO sometime 
> in the distant future if necessary.
> 
> But no-one ever got around to implementing this. More recently Alan 
> picked up it for a look, but it doesn't look like he's taken it anywhere 
> yet. Our client, GeoBC, would really like to see this get into the next 
> release, seems like we should be able to slide it into the 6.0 schedule? 
> So I'd like to confirm that Dan's earlier proposed method is still an 
> acceptable solution, and then go ahead and implement it and submit a 
> patch. I'd also appreciate any guidance or warnings about gotchas that I 
> might encounter with this approach.
> 
> Thanks,
> Chris
> 
> [1] http://trac.osgeo.org/mapserver/ticket/1688
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