1. “How I started to love GML” The new GPlates Markup Language James Clark, GPML Mad Scientist

2. In today's exciting presentation ● Reminder of what it is, and why we want to use it ● Why things get so complicated ● Brief brief brief overview of GPML structures because they're always changing ● Examples

3. GML ● What is it? – The fun happy next generation GIS standard format ● Why do we want to use it? – It's XML – Everyone else wants to ● Why aren't we using it already!? – Because it's very, very, complicated ● This isn't a bad thing

4. GP ML ● What is it? – The part of GML that we carve out ourselves, for GPlates to use ● Why should we have to do work? – GML provides a common framework of simple GIS primitives and structures that we can use as a base – It's not a magic bullet – As well as creating a data model for our plate tectonic stuff, we also need to make it use as much of these GML elements as possible, or there's no benefit

5. Why so complicated? ● GML makes us use objects for everything – Objects referring to objects referring to more objects with objects inside and a side order of objects – This is why my diagrams get so messy ● These objects must be arranged logically, but need different properties – i.e. Features which are reconstructable vs features which aren't ● It looks more confusing than it really is, just because one “thing” is represented with multiple elements in GML

6. Example of objects with different properties ● If we want to define a section of continental crust vs oceanic crust, we could use a simple polygon – But what about when the features that define that boundary move around? – What about overlapping features? ● The “Crust Boundary” element becomes a separate feature to the “Crust Boundary Segment” feature – It's one single entity to us, but in GML and GPML, it needs to be split up

7. Overlapping boundaries

9. Example markup ● Our basic simple unbroken-line Isochron Feature ● GPML defines it to have an age and a centre line

10. Example markup ● Inside the age property is a TimeInstant Feature ● Inside the centerLineOf property is a LineString Feature ● These are both GML constructs

11. Example markup 110 180.34 90.76 180.35 90.60 180.35 90.51 ● TimeInstant and LineString have their own properties ● Finally we can specify the actual age and geometry of the Isochron

12. Example markup 110 180.34 90.76 180.35 90.60 180.35 90.51 ● Time values need a reference frame ● Lat,Long values also depend on what CRS was used

13. And that was a simple example ● The SimpleIsochron element example has two properties defined by GPML – age, centerLineOf ● It also inherits additional properties from higher up in the GPML model – validTime, rotationHistory, oldPlatesHeader ● And inherits even more properties from the GML model – gml:name, gml:description, gml:boundedBy,...

15. Do not be afraid Be very, very frightened, Arthur Dent ● You will not have to actually write this markup yourself. That's the software's job. ● The multitude of objects and elements and features and properties and attributes may look scary and bloated... ● But it's better to have the ability to keep track of this data rather than forget it