[mapserver-dev] Label positioning around points

[thomas bonfort]

Christy, Havard,
I regret that you did not voice your concerns when the feature was up
for discussion on the mailing list.

http://lists.osgeo.org/pipermail/mapserver-dev/2012-March/012089.html
http://lists.osgeo.org/pipermail/mapserver-dev/2012-February/012002.html

On Fri, Sep 21, 2012 at 4:46 PM, Christy Nieman <cnieman at dmsolutions.ca> wrote:
> I appreciate that this discussion is coming back up!  I agree that the
> default order should be based on cartographic convention.  And while the 6.0
> and earlier order was not conforming to cartographic best practices,
> changing it with so little discussion/input/warning seems short-sighted as
> it drastically changes map output as compared to older mapserver versions.
>
>
> On 09/21/2012 10:26 AM, Havard Tveite wrote:
>>
>> I have seen the discussion, and the activity on github.
>> However, it seems as if the "decision" that was made then
>> was not based on cartographical best practice, as
>> documented in the cartography literature.
>> That is why I wanted to continue the discussion.
>>
>> In my opinion, the label positioning method used in
>> Mapserver should as much as possible be scientifically
>> based.  I would like to see documentation that supports
>> the proposed (master) method and the current (6.0) method.
>>
>> Håvard
>>
>> On 9/21/2012 4:02 PM, Stephen Woodbridge wrote:
>>>
>>> The was discussed a lot a few months ago.
>>>
>>> https://github.com/mapserver/mapserver/issues/4242
>>> https://github.com/mapserver/mapserver/issues/4249
>>> http://lists.osgeo.org/pipermail/mapserver-dev/2012-February/012003.html
>>>
>>> -Steve W
>>>
>>> On 9/21/2012 5:55 AM, Havard Tveite wrote:
>>>>
>>>> On 7/18/2012 5:45 PM, Christy Nieman wrote:
>>>> > Hi all,
>>>> >
>>>> > I was just wondering if the position order around points is still
>>>> open for comment.
>>>> >
>>>> > I know that there was discussion about this in the spring, and that a
>>>> change was implemented (though, I have to admit that I just noticed the
>>>> difference when comparing a tile cache that I created before the change
>>>> to one created a couple weeks ago). I'm not sure if having UC and LC as
>>>> the first two positions considered preferable to how the positioning
>>>> worked before. In a cluttered map, I find it non-intuitive to associate
>>>> a point with a label that is centred above/below it. I would personally
>>>> expect something like UR, UL, LR, LL, CR, CL, UC, LC. Map labelling
>>>> convention for points based on what I remember from my schooling and my
>>>> experiences since then seem to prefer UR and LR as the first locations
>>>> to consider.
>>>> >
>>>> > If it is not desirable to implement another change to the AUTO label
>>>> position order, perhaps it is necessary to consider the suggestion from
>>>> the spring to have the option of specifying a custom "AUTO" label
>>>> placement order (no idea how difficult this would be to implement).
>>>> >
>>>> > I just wanted to throw this out there.
>>>> >
>>>> > Regards,
>>>> > Christy
>>>>
>>>> I suggest that we do something about this, and I hope that it
>>>> can be done before 6.2 is released.
>>>>
>>>> I have found out that the AUTO label positioning is done in
>>>> mapdraw.c.
>>>> For points the AUTO behaviour has changed from 6.0 to master.
>>>> If the behaviour is to be changed, it should be done in
>>>> accordance with cartographical literature and best practice.
>>>>
>>>> In "Thematic Cartography and Geographic Visualization", 2nd
>>>> edition (Slocum, et. al., 2005), the following sequence is
>>>> listed for point labeling (referring to Pinhas Yoeli, 1972,
>>>> but modified to give preference to R placement - same as
>>>> for legends):
>>>> UR,LR,UL,LL,UC,LC,CR,CL.
>>>> CR and CL are placed last, because those positions can result
>>>> in "unfavourable optical coincidence" (Imhof 1975) - the point
>>>> symbol could be misinterpreted as a type character in the label.
>>>>
>>>> In "Elements of Cartography" (Robinson, et.al.), the following
>>>> sequence is listed for point labelling:
>>>> UR,UL,LR,LL,UC,LC (CR and CL are not included, but some more
>>>> variants of upper placement are listed as 7-9).
>>>>
>>>> The way I see it, it would be useful to change the behaviour
>>>> of Mapserver auto labelling.
>>>> 1) UR must be given the highest priority.
>>>> 2) LL, UC, LC, CR and CL should be given lowest priority.
>>>> 3) Someone must decide the sequence for LR and UL.
>>>>
>>>> These are then the two possible sequences:
>>>> UR,LR,UL,LL,UC,LC,CR,CL
>>>> UR,UL,LR,LL,UC,LC,CR,CL
>>>>
>>>> I see two options for 6.2:
>>>> a) modify mapdraw.c to revert to 6.0 behaviour.
>>>> b) modify mapdraw.c by changing the sequence to one that
>>>> is according to cartographical practice and literature.
>>>>
>>>> Håvard
>>>>
>>>> Mapserver label placement auto:
>>>> 6.0 (and 5.6):
>>>> Polygon:
>>>> positions[0]=MS_CC;
>>>> positions[1]=MS_UC;
>>>> positions[2]=MS_LC;
>>>> positions[3]=MS_CL;
>>>> positions[4]=MS_CR;
>>>>
>>>> Line:
>>>> positions[0]=MS_UC;
>>>> positions[1]=MS_LC;
>>>> positions[2]=MS_CC;
>>>>
>>>> Point:
>>>> positions[0]=MS_UL;
>>>> positions[1]=MS_LR;
>>>> positions[2]=MS_UR;
>>>> positions[3]=MS_LL;
>>>> positions[4]=MS_CR;
>>>> positions[5]=MS_CL;
>>>> positions[6]=MS_UC;
>>>> positions[7]=MS_LC;
>>>>
>>>> master:
>>>> Polygon:
>>>> positions[0]=MS_CC;
>>>> positions[1]=MS_UC;
>>>> positions[2]=MS_LC;
>>>> positions[3]=MS_CL;
>>>> positions[4]=MS_CR;
>>>> Line:
>>>> positions[0]=MS_UC;
>>>> positions[1]=MS_LC;
>>>> positions[2]=MS_CC;
>>>> Point:
>>>> positions[0]=MS_UC;
>>>> positions[1]=MS_LC;
>>>> positions[2]=MS_CR;
>>>> positions[3]=MS_CL;
>>>> positions[4]=MS_UR;
>>>> positions[5]=MS_UL;
>>>> positions[6]=MS_LR;
>>>> positions[7]=MS_LL;
>>>>
>>>>
>>>
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>>>
>>
>
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