[R-sig-Geo] add a field to sf object and point shape in kml

[Vijay Lulla]

Thank you, Barry!  Your explanation of how all these various
packages/libraries work is very helpful.  And so is your justification
(explanation?) of styling using extra column vs writeOGR options.
Appreciatively,
Vijay.

On Tue, May 7, 2019 at 3:23 PM Barry Rowlingson <b.rowlingson using gmail.com>
wrote:

>
>
> On Tue, May 7, 2019 at 6:11 PM Vijay Lulla <vijaylulla using gmail.com> wrote:
>
>> Good one Barry!  As far as I'm aware sf uses rgdal to write various file
>> formats and writeOGR has options called dataset_options and layer_options
>> which are considered experimental.
>>
>
> Not quite - `sf` uses the underlying C/C++ GDAL/OGR library directly. The
> `rgdal` package does the same. One doesn't use the other.
>
> To write KML the GDAL/OGR library uses either its "kml" or its "libkml"
> driver which is documented here:
>
> https://www.gdal.org/drv_libkml.html
>
> dataset_options and layer_options tend to be single value options per
> dataset and per layer - to set something per *feature* is going to need a
> lot more information, and having an extra attribute in the feature table
> (spatial data frame) seems reasonable.
>
> I've not quite understood all the libkml creation options relating to
> styles so there may be an easy way to do it but I don't think the overhead
> of an extra column is too much trouble.
>
> Barry
>
>
>
>> Do you know if either of these options can be used instead of creating a
>> new field/attribute for the sf dataframe?  More importantly, I would like
>> to know your opinion of using these options vs creating an attribute.
>> Thanks in advance,
>> Vijay.
>>
>> On Tue, May 7, 2019 at 11:07 AM Barry Rowlingson <b.rowlingson using gmail.com>
>> wrote:
>>
>>> On Tue, May 7, 2019 at 12:54 PM Marta Rufino <marta.m.rufino using gmail.com>
>>> wrote:
>>>
>>> > Hi,
>>> >
>>> > Two very simple question:
>>> >
>>> > 2)
>>> > Can we change the polygon col/fill and point shape/col when exporting
>>> sf
>>> > obejcts to kml, using the function:
>>> > st_write(sf.object, " sf.object  .kml", driver='kml')
>>> >
>>> >
>>> Setting styles for writing KML using GDAL/OGR is described here:
>>>
>>>
>>> https://gis.stackexchange.com/questions/297494/how-to-style-kml-through-libkml-layer-creation-options
>>>
>>> For example I have an sf data frame of Osprey tracking data (as points),
>>> and if I create a new field:
>>>
>>>
>>> osp$OGR_STYLE="PEN(c:#128020,w:5px)"
>>>
>>> and then:
>>>
>>> st_write(osp, "/tmp/osp.kml",driver="libkml")
>>>
>>> then the features in the KML get written with:
>>>
>>>          <LineStyle>
>>>             <color>ff208012</color>
>>>             <width>5</width>
>>>           </LineStyle>
>>>
>>> I realise now that "PEN" is probably wrong for point features, but it
>>> should all be explained in the google OGR style docs:
>>>
>>> https://www.gdal.org/ogr_feature_style.html
>>>
>>> and in the links in that GIS stack exchange question...
>>>
>>> Barry
>>>
>>>         [[alternative HTML version deleted]]
>>>
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>>>
>>
>>
>>

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