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

Smith, Michael D ERDC-CRREL-NH michael.smith at usace.army.mil
Fri Aug 27 09:52:42 EDT 2010

Jeff et al, 

My recommendation would be that if its a change in behavior, the make it
explicit to turn it on, not explicit to turn it off.

I do think this will be a very important addition to labeling.


Michael Smith
Remote Sensing/GIS Center
US Army Corps of Engineers
Hanover, NH

On 8/27/10  9:29 AM, "Alan Boudreault" <aboudreault at mapgears.com> 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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