[GPlates-discuss] Reverse reconstruct a raster in GPlates

Simon Williams simon.williams at sydney.edu.au
Tue Jul 16 13:46:00 AEST 2019


Hi Aleece,

Following on from John’s message and the link to the previous discussion of a similar issue - I don’t have much new to add, just a few points:

- if the geotiffs you are using are ones that contain single ‘z’ values, for example a topography in metres, then the suggested solutions should work well. If the geotiffs are rgb images, then the same solution could work but would need to be adapted to separate the red, green and blue values. At the step where the values need to be interpolated onto a new regular grid, the interpolation would need to force the interpolated values to be integers (e.g. some kind of nearest neighbour method)

- if you prefer to avoid python altogether and stick to GPlates, I believe (though haven’t tested) there is a workaround where you convert the raster values to a regular grid of points in a shapefile - each point in the shapefile would have the ‘z’ value in the attribute table corresponding to the coincident raster cell. Then load these into GPlates, assign plate ids at the reconstruction time, save the result and convert back to a raster (again, some interpolation required) outside GPlates. This approach could be very slow especially for a global raster with a high resolution. If you intend to do this for more than one raster, then investing the time to get the python option working is worth it.

Simon




On 16 Jul 2019, at 7:01 am, Michael Chin <michael.chin at sydney.edu.au<mailto:michael.chin at sydney.edu.au>> wrote:

Hi Aleece,

Here is the example code of using pyGPlates to reconstruct a raster. It is quite straightforward.

https://protect-au.mimecast.com/s/YdG_CBNZwLimkWjltzEbXl?domain=github.com<https://protect-au.mimecast.com/s/YdG_CBNZwLimkWjltzEbXl?domain=github.com>

________________________________
From: GPlates-discuss <gplates-discuss-bounces at mailman.sydney.edu.au<mailto:gplates-discuss-bounces at mailman.sydney.edu.au>> on behalf of John Cannon <john.cannon at sydney.edu.au<mailto:john.cannon at sydney.edu.au>>
Sent: Monday, 15 July 2019 10:20 PM
To: GPlates general discussion mailing list
Cc: Nanfito, Aleece
Subject: Re: [GPlates-discuss] Reverse reconstruct a raster in GPlates

Hi Aleece,



Unfortunately it’s not possible in GPlates. Also the Assign Plate IDs dialog is only for vector data.



However, this post by Simon Williams talks about his pyGPlates code to reconstruct a raster from one time to another:
https://protect-au.mimecast.com/s/ZeThCD1jy9tmWYqOt5X1xS?domain=mailman.sydney.edu.au<https://protect-au.mimecast.com/s/ZeThCD1jy9tmWYqOt5X1xS?domain=mailman.sydney.edu.au>



My understanding (Simon can correct me if I’m wrong) is he essentially:

  1.  has a grid of points at the ‘to’ time,
  2.  assigns them plate IDs using the static polygons (reconstructed to the ‘to’ time),
  3.  reconstructs the points back to the ‘from’ time (using their newly assigned plate IDs),
  4.  samples the raster (which is assumed to represent raster data at the ‘from’ time) at those reconstructed point locations,
  5.  writes out the sampled values at the reconstructed points as a new raster at the ‘to’ time.



In your case the ‘from’ time is the time of your raster, and the ‘to’ time is any time you want to reconstruct it to. At least that’s my understanding 😊  So that’s a good example of how to use pyGPlates to reconstruct a raster by reconstructing points and sampling rasters.



Regards,
John



From: GPlates-discuss <gplates-discuss-bounces at mailman.sydney.edu.au<mailto:gplates-discuss-bounces at mailman.sydney.edu.au>> On Behalf Of Nanfito, Aleece
Sent: Monday, 15 July 2019 6:53 AM
To: gplates-discuss at mailman.sydney.edu.au<mailto:gplates-discuss at mailman.sydney.edu.au>
Subject: [GPlates-discuss] Reverse reconstruct a raster in GPlates



Hello –
This is likely a novice question, but I am having problems in GPlates trying to reverse reconstruct a raster, in past time/position, to present day. I reconstruct the plate polygons to the past time represented in the raster, import the raster, and then connect the raster to the plate polygons.  The raster is automatically cut by the present day position of the plates. I’ve tried this exercise on rasters (geotiffs) with a global extent and regional extent. The raster and plate polygons are nicely aligned in the past position, before I connect the two. Is there a way to specify a past time/position for when the raster-to-polygon connection occurs?



I’ve also tried using the Assign Plate ID tool on the rasters. I can select all specifications within the assign plate id dialog box, but the process seems to immediately cancel/fail without providing an error.



I appreciate any input on whether this task is possible in GPlates & solutions, or any possible workaround in PyGPlates. Thanks so much in advance!



Best regards,
Aleece





<image002.png>

Aleece Nanfito
Geologist
aleece.nanfito at bhpbilliton.com<mailto:aleece.nanfito at bhpbilliton.com>
1500 Post Oak Blvd.
Houston TX 77056 USA



bhpbilliton.com<https://protect-au.mimecast.com/s/Z_7cCE8kz9tGz4L6HpxApL?domain=bhpbilliton.com>





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