[mapserver-users] Re: ANGLE FOLLOW and Label Offset (v. 5.6.6)

Tue Jun 7 16:45:44 EDT 2011

Brent, Thomas,

Could we optionally allow GEOMTRANSFORM inside the LABEL and here it 
would be only used for the label. I guess the ambiguous part might be 
does this GEOMTRANSFORM in the label work based on the original geometry 
or LAYER level GEOMTRANSFORM that might precedes it.

This seems like the simple clean solution to me.

Thoughts?

-Steve W

On 6/7/2011 9:55 AM, Brent Fraser wrote:
> Thomas,
>
> Yes, I've been trying to come up with good map file syntax to indicate
> labeling of the transformed geometry. Currently mapserver allows:
> - transformed original geometry (buffer, difference)
> - augmented original geometry (bbox, start/end, vertices)
> - rendered label geometry (labelpoint, labelpoly)
>
> but it doesn't label transformed geometry, only original geometry. The
> main problem (from a user interface perspective) is how to relate
> transformed geometry to the label specification.
>
> One solution is to allow a LABEL object within a STYLE object:
>
> CLASS
> NAME 'Streams'
> STYLE
> GEOMTRANSFORM (buffer([shape], 5))
>
> LABEL
> usual label settings
> END # Label
> END # Style
>
> but that's a little strange as STYLE objects are currently allowed
> within LABEL objects.
>
> Another solution is to have "named" geometry and reference it in the
> LABEL object (and keep the existing CLASS/STYLE/LABEL structure):
>
> CLASS
> NAME 'Streams'
> STYLE
> GEOMTRANSFORM my_label_shape = (buffer([shape], 5))
> END # Style
>
> LABEL
> usual label settings
> GEOMETRY my_label_shape
> END # Label
>
> And I'm sure there are other (and hopefully better) solutions.
>
> Best Regards,
> Brent Fraser
>
>
> On 6/6/2011 11:02 AM, thomas bonfort wrote:
>> Yes, the resulting shape seems like a nice candidate for offseting
>> labels, but the problem with buffer is you will have more difficulty
>> in deciding what is to the left from what is to the right of the line.
>> We'd also have to make sure that the buffer operation is not too
>> costly on cpu cycles.
>> Anyways, until geomtransform is not applied at the layer level, there
>> is no way to use this method as the label does not operate on the
>> transformed geometry.
>>
>> On Mon, Jun 6, 2011 at 17:30, Brent Fraser<bfraser at geoanalytic.com>
>> wrote:
>>> Steve,
>>>
>>> I think just buffering the line would apply a type of smoothing (see
>>> attached image). Using the resulting buffer line (or perhaps doing some
>>> simple line smoothing on it) for labeling would be good enough.
>>>
>>> Best Regards,
>>> Brent Fraser
>>>
>>>
>>> On 6/6/2011 9:04 AM, Stephen Woodbridge wrote:
>>>> Duh! you are correct, I always forget this point until I after my
>>>> second
>>>> cup of coffee has kicked in :)
>>>>
>>>> That article looks very interesting, I have to read up on that.
>>>>
>>>> In a past career in computer aided design and manufacturing, we used
>>>> the
>>>> idea of a rolling ball offset because it modeled a milling machine. The
>>>> rolling ball offset is defined as the curve traced by the center of
>>>> a ball
>>>> of a given radius as you roll it along a curve. The circumference of
>>>> the
>>>> ball can not cross over the original curve so for tight "S" curves
>>>> if the
>>>> diameter of the ball is larger than the gap in the "S" then the ball
>>>> does
>>>> not enter the gap but floats over it. This same concept would make
>>>> for well
>>>> behaved and good looking labels along tight twisty paths like rivers
>>>> and
>>>> roads.
>>>>
>>>> Another idea for smoothing out curves for labeling might be to apply
>>>> an N
>>>> point moving average and allow that to be the label path. I don't
>>>> think this
>>>> has been mentioned as an option in the past.
>>>>
>>>> -Steve W
>>>>
>>>> On 6/6/2011 10:20 AM, thomas bonfort wrote:
>>>>> There are two problems with the solution you propose:
>>>>> - if you offset the geometry in postgis, the distance of the offset
>>>>> will be in geographical units, i.e. it will not give correct results
>>>>> at all scales when rendered with mapserver (what you basically want is
>>>>> to offset the line by a number of pixels roughly equal to the size of
>>>>> the font used for labelling)
>>>>> - angle follow on offset line should probably be done on a
>>>>> simplified/smoothed geometry. see
>>>>> http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.24.6970 .
>>>>> Ideally someone will want the feature badly enough to fund it :)
>>>>>
>>>>> --
>>>>> thomas
>>>>>
>>>>>
>>>>>
>>>>> On Mon, Jun 6, 2011 at 16:02, Stephen Woodbridge
>>>>> <woodbri at swoodbridge.com> wrote:
>>>>>> There was some recent discussion on the dev list about potentially
>>>>>> using
>>>>>> the
>>>>>> GEOMTRANSFORM to do something like a single sided offset then
>>>>>> using that
>>>>>> to
>>>>>> apply the label to. BUT I do not think that has been implemented
>>>>>> yet in
>>>>>> mapserver.
>>>>>>
>>>>>> Google for "mapserver geomtransform" also look at "geoprocessing" for
>>>>>> some
>>>>>> other ideas.
>>>>>>
>>>>>> Anyway, you might be able to do what you want if you:
>>>>>>
>>>>>> 1. import your data into PostGIS
>>>>>> 2. create offset geometry in another table
>>>>>> 3. export that table to a shapefile
>>>>>> 4. then label that as an annotation layer so you do not draw the
>>>>>> geometry
>>>>>> only the label and use the original data to draw the grometry ie: two
>>>>>> layers.
>>>>>>
>>>>>> I have not tried this, but it might solve your problem.
>>>>>>
>>>>>> -Steve W
>>>>>>
>>>>>> On 6/6/2011 9:48 AM, uvg wrote:
>>>>>>> Thank you, Thomas.
>>>>>>> Are there any workarounds for this problem?
>>>>>>> Is there 'best practices' for the problem?
>>>>>>> Maybe unvisible layer or other?
>>>>>>> 06.06.2011, 17:35, "thomas bonfort [via OSGeo.org]"<[hidden email]
>>>>>>> </user/SendEmail.jtp?type=node&node=6445194&i=0>>:
>>>>>>>
>>>>>>> The status has not changed: label follow with offset is not
>>>>>>> supported.
>>>>>>>
>>>>>>> regards,
>>>>>>> thomas
>>>>>>>
>>>>>>> On Mon, Jun 6, 2011 at 15:33, uvg<[hidden email]> wrote:
>>>>>>>
>>>>>>>> Hi all!
>>>>>>>> Sorry for my bad English.
>>>>>>>>
>>>>>>>> I am trying to achieve is a label that follows the rivers that is
>>>>>>> also
>>>>>>>> OFFSET so that
>>>>>>>> the label does not 'above' on the line for the river.
>>>>>>>>
>>>>>>>> Sample code of mapfile:
>>>>>>>>
>>>>>>>> LABEL
>>>>>>>> COLOR 0 40 255
>>>>>>>> FONT "arial-italic"
>>>>>>>> TYPE truetype
>>>>>>>> SIZE 7
>>>>>>>> OFFSET 5 0
>>>>>>>> ANGLE FOLLOW
>>>>>>>> POSITION LC
>>>>>>>> FORCE true
>>>>>>>> PARTIALS FALSE
>>>>>>>>
>>>>>>>> END
>>>>>>>>
>>>>>>>> "OFFSET" does not work.
>>>>>>>> How can I offset a label?
>>>>>>>>
>>>>>>>> I found a message posted for a long time:
>>>>>>>> click here.
>>>>>>>
>>>>>>> View this message in context: Re: ANGLE FOLLOW and Label Offset (v.
>>>>>>> 5.6.6)
>>>>>>>
>>>>>>>
>>>>>>> <http://osgeo-org.1803224.n2.nabble.com/ANGLE-FOLLOW-and-Label-Offset-v-5-6-6-tp6445138p6445194.html>
>>>>>>>
>>>>>>> Sent from the Mapserver - User mailing list archive
>>>>>>> <http://osgeo-org.1803224.n2.nabble.com/Mapserver-User-f1969211.html>
>>>>>>>
>>>>>>> at
>>>>>>> Nabble.com.
>>>>>>>
>>>>>>>
>>>>>>>
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