[mapserver-dev] RFC 89 Layer Geomtransform: Call for vote

[Alan Boudreault]

I've just added these notes in the RFC. Should be updated soon.

Alan

On 13-02-19 11:09 AM, Stephen Woodbridge wrote:
> On 2/19/2013 10:30 AM, Alan Boudreault wrote:
>> Thanks Daniel for the good explanation. If everyone agree, I'll add this
>> information in the RFC.
>>
>> Steve, in the code, if the UNITS is specified... it will be used. Else,
>> I'll try to get the projection unit, and finally default to degree. Is
>> this ok?
>
> Yes, that sounds like the best effort that you can do. I agree with the
> change. If the user needs it to be more precise then they need to
> specify UNITS. Please add this detail to the RFC because it will need to
> be documented when everything is done.
>
> Thanks,
>    -Steve W
>
>> Thanks,
>> Alan
>>
>> On 13-02-19 10:12 AM, Daniel Morissette wrote:
>>> Alan, All,
>>>
>>> As we looked into the implementation details with Alan, we found out
>>> that the STYLE-level GEOMTRANSFORM receives a shape in pixel
>>> coordinates, whereas the LAYER-level GEOMTRANSFORM will receive the raw
>>> shape in ground coordinates (meters, degrees, etc.)
>>>
>>> This poses a little potential for confusion in the user's mind as the
>>> argument to methods such as simplify() must be in the same units as the
>>> coordinates of the shapes at that point of the rendering workflow, i.e.
>>> pixels at the STYLE-level and in ground units at the LAYER-level.
>>>
>>> e.g.
>>>
>>> LAYER NAME "my_layer"
>>>    TYPE LINE
>>>    STATUS DEFAULT
>>>    DATA "lines.shp"
>>>    GEOMTRANSFORM (simplify([shape], 10))  ## 10 ground units
>>>    CLASS
>>>      STYLE
>>>        GEOMTRANSFORM (buffer([shape], 5)  ## 5 pixels
>>>        WIDTH 2
>>>        COLOR 255 0 0
>>>      END
>>>    END
>>> END
>>>
>>>
>>> It would be possible (but messy) to include some maths at the
>>> layer-level to allow passing a value in pixels at the layer level as
>>> well. This way things would be consistent between STYLE level and LAYER
>>> level as we would always pass args in pixels, but this may not be what
>>> we want in lots of cases, for instance if a LAYER-level GEOMTRANSFORM is
>>> used to simplify shapes in a WFS context where pixel size makes no or
>>> little sense.
>>>
>>> It is also not possible at all to deal with values in ground units at
>>> the style level because we do not have information about map cellsize at
>>> that level in the code (so passing values in ground units at the style
>>> level is not an option without messy code changes)
>>>
>>> Note that in cases where we want to pass a pixel value at the layer
>>> level, a [map_cellsize]  variable will be available, e.g.
>>>
>>> LAYER NAME "my_layer"
>>>    TYPE LINE
>>>    STATUS DEFAULT
>>>    DATA "lines.shp"
>>>    # 10 * [map_cellsize] == 10 pixels converted to ground units
>>>    GEOMTRANSFORM (simplify([shape], [map_cellsize]*10))
>>>    ...
>>>
>>>
>>> It seems that our best option would be to keep the values as pixels at
>>> the style level and ground units at the layer level, and properly
>>> document the difference, and hope that users won't be too confused.
>>>
>>> What do you all think?
>>>
>>> Daniel
>>>
>>>
>>>
>>> On 13-02-14 6:58 AM, Alan Boudreault wrote:
>>>> Hi devs,
>>>>
>>>> Please vote on RFC 89, Layer Geomtransform (
>>>> http://mapserver.org/trunk/development/rfc/ms-rfc-89.html )
>>>>
>>>> I'll start with my +1.
>>>>
>>>> Thanks,
>>>> Alan
>>>>
>>>
>>>
>>
>>
>
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-- 
Alan Boudreault
http://www.mapgears.com/