[aspect-devel] ASCII files - Cut a 2D spherical model in slices

[Rene Gassmoeller]

On 21.01.2018 00:55, Wolfgang Bangerth wrote:
>> The new question is: I implemented GPlates velocities as boundary
>> conditions for my 2D spherical model.The slice at which my first
>> model was cut was the geographic equator (the default Point one and
>> Point two section of the cookbooks...). Since I would like to cut my
>> model using different coordinates, I tried to change them several
>> times (paying attention to change them to colatitude and longitude
>> -in radians-), but what I got was always a cut slice through the
>> geographic equator.
>> I visualize it with Paraview, using the coastline file.
>> What am I missing?
>
> I don't know for sure, but this is how this sounds to me: When you do
> a 2d computation, ASPECT does this in x-y coordinates that when you
> naively visualize it in Paraview is embedded into a 3d coordinate
> system in the equatorial plane. But that doesn't mean that the slice
> you are computing on actually *is* in the equatorial plane -- it's
> just that the 2d slice is embedded into the 3d coordinate system that
> way. You'll have to figure out a way to embed it so that it matches
> the actual slice you compute on.

Just to clarify Wolfgang's comment: When you change the coordinates for
reading in the GPlates velocities, ASPECT does not 'actually' change the
geometry it uses (it will still lie in the equatorial plane). Instead it
rotates coordinates internally, before looking up the velocities from
the GPlates files. Thus, you should see a change in surface velocities
of your model, but when you plot the coastlines file, it will appear
unchanged. But what you can do is use the 'Paraview rotation angles'
that are written at the beginning of the model run (or the inverse
angles that are also written) to set up a 'Transform' filter in Paraview
that either rotates the geometry into the actual orientation (the one
set of angles) or rotates the coastlines into the orientation that is
equivalent to the internal rotation ASPECT uses (the other set of angles).

Best,
Rene

>
> Best
>  W.
>