gtCalculateGrain: let's re-use some existing function

Signed-off-by: Nicola Vigano <nicola.vigano@esrf.fr>

4_grains/gtCalculateGrain.m

@@ -91,7 +91,6 @@ detgeo = parameters.detgeo;
 
 %%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 % % Crystallography from parameters file
-lambda = gtConvEnergyToWavelength(parameters.acq.energy);
 
 %disp('Translating Miller indices into normalized cartesian coordinates for plane normals')
 Bmat = gtCrystHKL2CartesianMatrix(cryst.latticepar);
@@ -128,11 +127,9 @@ end
 % d-spacing after applying the strain tensor
 dsp_d = drel .* dsp_ref;
 
-% Bragg angles theta in the deformed state
-sinth = 0.5 * lambda ./ dsp_d;
-
-% New sin(theta) in deformed state is inversely proportional to elongation
-theta = asind(sinth);
+% Bragg angles theta and sin(theta) in deformed state is inversely proportional
+% to elongation
+[theta, sinth] = gtCrystTheta(dsp_d, parameters.acq.energy);
 
 % The plane normals need to be brought in the Lab reference where the
 % beam direction and rotation axis are defined.