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Polygon-based occurrence data #112

Closed ansell closed 6 years ago

ansell commented 6 years ago

The ALA has a potential data provider who has a high quality weed survey and treatment dataset that contains fairly precise polygon data and we would like to include it. Does Darwin Core allow for polygon-based occurrence data currently?

Translating the polygons into "lat+long+radius" is a non-starter in this case due to the precise shape of the polygons and the likelihood of the point being nowhere near the polygon itself and hence useless in terms of reusing the translated dataset.

tucotuco commented 6 years ago

@ansell Darwin Core does indeed support geometries in the format of Well-Known Text (WKT) in the footprintWKT field. I have added documentation about this on the Georeferences Questions & Answers page at https://github.com/tdwg/dwc-qa/wiki/Georeferences#footprintwkt.

wardappeltans commented 6 years ago

We do use our footprintWKT in OBIS for polygons (e.g. habitats) and line strings (e.g. trawls). You might be interested in the OBIS geocoding tool at http://iobis.github.io/map/, which has an option to generate WKT. See short video tutorial at https://www.youtube.com/watch?time_continue=84&v=XB4rUYhb_ok.

The OBIS recommendation is to provide the midpoint and radius in addition to footprintWKT for polygons and line strings.

A useful read for the issue when the midpoint is outside the polygon: https://blog.mapbox.com/a-new-algorithm-for-finding-a-visual-center-of-a-polygon-7c77e6492fbc. Another option to show these polygons as points on a map, see https://i.stack.imgur.com/cTLuj.jpg

tucotuco commented 6 years ago

Thanks, Ward. I have added the information you provided to the Georeferencing Questions & Answers wiki page. Much appreciated.

On Sat, Nov 4, 2017 at 10:20 AM, Ward Appeltans notifications@github.com wrote:

We do use our footprintWKT in OBIS for polygons (e.g. habitats) and line strings (e.g. trawls). You might be interested in the OBIS geocoding tool at http://iobis.github.io/map/, which has an option to generate WKT. See short video tutorial at https://www.youtube.com/watch? time_continue=84&v=XB4rUYhb_ok.

The OBIS recommendation is to provide the midpoint and radius in addition to footprintWKT for polygons and line strings.

A useful read is for the issue when the midpoint is outside the polygon: https://blog.mapbox.com/a-new-algorithm-for-finding-a- visual-center-of-a-polygon-7c77e6492fbc. Another option to show these polygons as points on a map, see https://i.stack.imgur.com/cTLuj.jpg

— You are receiving this because you modified the open/close state. Reply to this email directly, view it on GitHub https://github.com/tdwg/dwc-qa/issues/112#issuecomment-341896421, or mute the thread https://github.com/notifications/unsubscribe-auth/AAcP6-uzwsBdYAG3aIr6RVaxC5bq0ML1ks5szGSOgaJpZM4QQeOe .

ansell commented 6 years ago

Thanks, the footprintWKT field didn't catch my eye when I was looking through it before. The data provider has got back to me to say that they are able to generate representative "mid-points" to add to the source data, even though some of the shapes are not really amendable to reduction. I will mention to them to also include WKT for the polygons before they are reduced.