minor fix in case one wants to enter a drift vector manually

Signed-off-by: Wolfgang Ludwig <wolfgang.ludwig@esrf.fr>

1_preprocessing/gtPreprocessing.m

@@ -250,8 +250,13 @@ disp(' ')
 
 % this is the time to analyse a calibration or quali scan to determine
 % sample drifts
-ydrift=zeros(1, totproj);  % default values for drift
-zdrift=zeros(1, totproj);
+if isempty(parameters.prep.udrift)
+    ydrift=zeros(1, totproj);  % default values for drift
+    zdrift=zeros(1, totproj);
+else
+    ydrift=parameters.prep.udrift;
+    zdrift=parameters.prep.vdrift;
+end
 
 check = inputwdefault('Do you want to perform sample drift analysis for this measurement? [y/n]', 'n');
 if strcmpi(check,'y')