RBG colour map and real values?

[xshang93]

Hi! It's been a while and I missed it here!

Does anyone know how the colour map RGB values are translated from the real values? For example, how is a crystal orientation, say (37, 81, 112) in Euler convention translated to RGB values, if the default 'viridis' colour map is used?

[rquey]

Welcome back @xshang93!

It's described in, e.g., -datacellcolscheme:

• For real values, the maps are described here: https://neper.info/doc/exprskeys.html#color-maps-for-real-values, and they are viridis, etc.
• For orientations, the typical maps are rodrigues and ipf, and they are shown in this tutorial. True that they are not described in detail in the documentation. For rodrigues, the color is defined as {R,G,B}=255 x (r_i + sqrt(2) - 1) / (2 * (sqrt(2) - 1)), for cubic crystal symmetry.

I'll complete the documentation.

[mkasemer]

You can calculate the angle between the c-axis and any other vector (e.g., a sample axis / loading direction) readily with a rotation matrix / dot product between two vectors. From there, you can write this angle (calculated per-element) to a VTK file and visualize via Paraview. Neper may already be able to do this via mathematical manipulation of FEPX output (see neper -S section of the manual). Be careful to only consider angles 0-90, as anything less or greater is redundant / symmetrically equivalent.

[rquey]

Once the values are computed and recorded to a file, you can simply use -V -dataelsetcol "real:file(...)" (or -dataeltcol ... for per-element) to visualize.

If you have a simulation directory, you can add the data to it using -S -reselset "<res>:file(<basename>)" (you'll need all <basename>.step# files) and then simply use -V -dataelsetcol real:<res> to visualize.

[xshang93]

Amazing! Thanks @mkasemer and @rquey for the directions. I will test it out!

[xshang93]

Hi @mkasemer , sorry I just have an add-on question on FEPX: What we have been discussing here is only in concern with visualization right? I.e., when running simulations in FEPX, the crystal symmetries (and the corresponding orientations) will still be regulated as specified in the .config file, regardless how the crystal symmetry is specified in Neper? Moreover I guess redundant orientations will not cause any trouble to the simulation results, am I correct?

[mkasemer]

FEPX only cares about crystal orientation for elastic / plastic (slip) behavior. Orientations can be redundant - they will ultimately be converted to rotation matrices in-code.