[mapserver-dev] RFC-60: Label enhancement to skip ANGLE FOLLOW labels with overlapping chars

Stephen Woodbridge woodbri at swoodbridge.com
Fri Aug 27 10:25:08 EDT 2010

What happens if you set the value whatever the default value for 
geoserver is? what happens at 25 degrees in your example. BTW, these 
example images are really useful to understand the behavior.

-Steve W

On 8/27/2010 9:29 AM, Alan Boudreault wrote:
> Hi Jeff,
> My concern about discarding labels by default is about all maps with text
> labels. I've attached two images which show what I mean. It's probably not the
> best example since most of the roads do not curve though. The MAXOVERLAPANGLE
> value is 22.5, no REPEATDISTANCE/MINDISTANCE. In this case, there are two bad
> labels that have been discarded. cool! If you look further you should see a
> roads labeled "Whites Creek Lane" that have also been discarded. (Do not care
> of the new label with the same text that appears below, it's another feature..
> so let's say it's not the same text so it is not related to the issue) But
> that label was ok in my point of view. Imagine if the map had a lot of curved
> roads.
> I don't disagree totally with the idea to but the label discarding by default
> with an absolute value... but I think 22.5 is a little bit too small and I
> want to be sure that the change wont affect users maps. Perhaps I just see the
> issue bigger than it is... but I'm not a mapserver user so.. :)
> Thanks for your comments!
> regards,
> Alan
> On August 27, 2010 04:37:21 am Jeff McKenna wrote:
>> Hi Daniel and Alan,
>> Thanks for producing this RFC and doing the background tests.  (I
>> especially like the map image showing the BBoxes of the individual label
>> characters, which really helps to understand the angle between some
>> label characters
>> (http://trac.osgeo.org/mapserver/attachment/ticket/3523/mapserver-label-box
>> es.png).
>> I have the benefit of sitting beside Andrea from GeoServer right now,
>> and I have asked him specific details of how GeoServer handles this same
>> issue.  As I understand, this is how it works for GeoServer:
>> 1) user can modify angle to use between characters with a MAXANGLEDELTA
>> parameter
>> (http://docs.geoserver.org/2.0.x/en/user/styling/sld-reference/labeling.htm
>> l#labeling-max-angle-delta) 2) by default GeoServer uses a hardcoded value
>>   of something like 25 (Andrea wasn't sure about exact value at the time)
>>   and discards labels with angles higher than that
>> So, regarding RFC-60, I support the addition of the MAXOVERLAPANGLE
>> parameter (I like this name better than GeoServer's, at least I can
>> understand what the parameter means by the name).
>> However I disagree with the RFC's statement "The default behavior of the
>> software if this parameter is not set will remain unchanged, i.e. this
>> test will be disabled by default and no labels will be skipped.".  I
>> don't see how any user would ever want a high angle between their label
>> characters, so let's set a default value (22.5) and discard labels with
>> higher angles between characters.
>> Aside: in the case of labelling contours for the benchmarking exercise,
>> Andrea showed me his config file and he sets a MAXANGLEDELTA of 30.
>> -jeff
>> On 10-08-26 10:25 PM, Daniel Morissette wrote:
>>> Hi Devs,
>>> As part of the FOSS4G 2010 Benchmarking exercise, we have discovered
>>> that MapServer did a poor job at labeling contour lines whereas others
>>> such as GeoServer didn't suffer of the same problem. It turns out that
>>> GeoServer detects and skips those problematic labels, leaving room for
>>> other/better labels to fall in the spot left available by the skipped
>>> label.
>>> Alan has been doing some experiments around this problem and we have
>>> come up with a RFC that we would like to discuss. To make a long story
>>> short we are proposing that we do the same as GeoServer and offer an
>>> optional mechanism to detect and skip those labels.
>>> Please have a look at RFC-60 and let us know what you think:
>>>     http://mapserver.org/development/rfc/ms-rfc-60.html
>>> The discussions in ticket 3523 may also be of interest:
>>>     http://trac.osgeo.org/mapserver/ticket/3523
>>> And finally there is also ticket 2221 discussing more general labeling
>>> enhancements that this RFC does not aim to address:
>>>     http://trac.osgeo.org/mapserver/ticket/2221
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