gtRenderGrains: fixed labgeo usage

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

6_rendering/gtRenderGrains.m

@@ -185,11 +185,11 @@ end
 %h.fig = figure();
 %h.axes = axes('parent', h.fig);
 
-parameters = [];
-load('parameters.mat');
+parameters = gtLoadParameters();
 labgeo  = parameters.labgeo;
-if isempty(par.pxsize)
-    par.pxsize = (labgeo.pixelsizeu + labgeo.pixelsizev)/2;
+recgeo  = parameters.recgeo;
+if (isempty(par.pxsize))
+    par.pxsize = mean(recgeo.voxsize);
 end
 
 if isempty(par.hf)