Right, so I’ve been using GPlates for a long while now, for the purpose of worldbuilding (for fiction). Today I’ve run into an unexpected problem. When I try to create topological boundary polygons from existing features (in this case, sections of coastline), the result is either a completely invisible feature, or a polygon consisting of only one of the features I selected for the polygon.
Here is an example of one of the polygons I’m trying to create:
And here is the result:
[Guess I’ll have to put this image in a reply, due to new user image per post limit]
What is happening here? The ends of each coastline segment feature are snapped to one another, so I do not understand why this is happening. It’s been a long while since I’ve actually used the topology tool, so maybe I’m doing something basic wrong here.
Swift help would be very much appreciated.
Hi,
In your second screenshot it looks like the topology is not finding all of its boundary coastline features. There can be a few reasons for this, but typically it’s related to the feature IDs in some way.
One possibility is you are using Shapefile for the regular features (coastline) but have not saved it using GPlates prior to building your topology as mentioned in this post.
Another possibility is you have multiple features (coastline) with the same feature ID as mentioned in this post. Perhaps due to a manual copy’n’paste of a coastline GPML file.
If it’s neither of those issues then feel free to send me the files that reproduce the problem and I’ll have a look.
PS: It’s also worth being aware that the menu item View > Geometry Visibility > Show Topological Sections is disabled by default as covered in detail in this post. But I don’t think that’s affecting your problem.
Regards,
John
Hi John. Thanks for your response.
I haven’t actually assigned any IDs to any of the features at this time, as I am not going to be reconstructing any plate motion at this time, nor have I even built plates yet (except roughly, but all the boundaries need to be redone). I’m not sure how I would go about deciding which IDs to assign the features, especially if (as it seems in your reply) each feature in a topology must have a unique ID.
However, I’ve found that I could successfully build a topology from the coastline segments of one small landmass, and again those segments have no IDs.
Also, I’ve been doing everything from within GPlates, so all features have been saved from within GPlates.
I’ll send the file to you later today, when I have access to my computer.
Sorry, I meant feature IDs, you might be thinking of plate IDs. You don’t normally need to worry about feature IDs, it’s normally an internal detail but can become an issue in certain situations with topologies.
I’ll have a look at your files once you’ve sent them.
Regards,
John
I’m not entirely sure how I ought to be sending the files, so I just uploaded the relevant files to Google Drive: GPlates Thingies – Google Drive
I’ve also checked, and each feature (coastline segment) does have a unique feature ID.
I had a look at your three files (nice contours!) but I don’t see your topological features. Can you send me the file that you saved them to (when you built them in your first screenshot)?
I only need them so I can see which feature IDs they reference (and then see if they’re missing or duplicated among your coastlines).
Thanks,
John
Thanks. 
Right, I added the topology file to the folder. Just has the one topology.
Thanks. At present day (0 Ma) it works fine for me, everything looks good. And then everything disappears at 1 Ma (and older) because the time period (on both the sole topology and the coastlines) is set to 0Ma → 0Ma (begin → end).
If you make the begin times non-zero (on both topology and coastlines) you should be fine.
As for your second screenshot (with the sole coastline section wrapping back around on itself) I was able to replicate that by making the begin time non-zero on both the topology and that one coastline piece, and then setting the time slider to 1Ma (so that all the other coastlines disappeared except that one piece). In this case the topology is only able to find that one coastline section existing at 1Ma (and ignores the rest).
Regards,
John
I only work on 0Ma. Bizarre that it’s fine for you, but not for me…
It is a bit odd, what platform are you running on (and which GPlates version)? I might try the same, or similar, if I can. And you’re sure that loading those exact files (that you sent) and only those files does not work on your system at present day?
You know, I was too dumb to check. It works with just those files.
I found the issue. There’s an old layer called “Bodies of Water”, which countains duplicates of the coastlines. Unloaded it, and it works!
Thanks so much for steering me in the right direction! And sorry for wasting your time with my idiocy…
No problem I’ve done it myself (in my case loaded the same file twice).
