| 824 | | The FIX operation is used after civ to remove false vectors, using different criteria: -''' {warning flags:} ''' these are flags (vec_F) indicating problems with the image correlation process: -*vec_F(i)=0 or 1 : default , the processing is fine |
| 825 | | -*vec_F(i)=-2: the maximum of the correlation function is close to the border of the search box (at a distance of two pixels or less), so that its maximum cannot be reliably obtained: the search domain is too small |
| 826 | | -*vec_F(i)=2: (only in civ1) we keep the less accurate Hart result (resulting from combining correlation functions from neighborhing points) and vec_C(i)=-1 is chosen by convention. Reference: Hart D. P. (2000) 'PIV error correction',{ Exp. Fluids} '''29''', 13-22. |
| 827 | | -*vec_F(i)=3: the optimisation of the correlation function is unstable or local Intensity rms of the image =0 |
| 828 | | -*vec_F(i)=4:only in civ2: the difference between the estimator and the result is more than 1 pixel. The two criteria, vec_F(i)=-2, and 3, should be selected (default options). The criterium vec_F=2 (Hart) should not be selected, while vec_F=4 (for civ2) could be selected only for excellent data (otherwise it may be too strict). -''' {Threshold on the image correlation} ''' (vec_C) can be introduced by the edit box [thresh_vecC] (value between 0 and 1). It removes vectors with poor correlation. -''' {Threshold on the velocity modulus } ''' (expressed in pixels): it can remove either too small values (menu '''[inf_sup1]''' set to '<'), or excessive values (menu '''[inf_sup1]''' set to '>'). Erratic zero velocity vectors, produced by a fixed image background, can be eliminated by this criterium. These criteria can be as well applied to the difference with a reference field, defined by a file series (edit box '''[ref_fix1]''') and a field inside the file (menu '''[field_ref1]'''). -''' {Mask fix:} ''' It has the same effect as the one used in civ1, but the removed vectors are kept in memory, labelled as false. -''' {Manual fix:} ''' Interactive fixing with the mouse is also possible, see [section 4.2->#4.2]. |
| 829 | | |
| 830 | | -''' {Code for FixFlag:} ''' -*FixFlag(i)=0 :default, everything is fine -*FixFlag(i)=1. : value 1 for the second digit: vector removed by criteria on vec_F or/and low correlation value -*FixFlag(i)=1..: value 1 for the third digit: vector selected by a criterium of difference with another field, for instance filter, or a field with differnt time interval. -*FixFlag(i)=...1, 2, 3 different criteria for elimination set by the program Fix of CIVx (not yet documented). |
| | 824 | The FIX operation is used after civ to remove false vectors, using different criteria: -''' {warning flags:} ''' these are flags (vec_F) indicating problems with the image correlation process: *vec_F(i)=0 or 1 : default , the processing is fine |
| | 825 | *vec_F(i)=-2: the maximum of the correlation function is close to the border of the search box (at a distance of two pixels or less), so that its maximum cannot be reliably obtained: the search domain is too small |
| | 826 | *vec_F(i)=2: (only in civ1) we keep the less accurate Hart result (resulting from combining correlation functions from neighborhing points) and vec_C(i)=-1 is chosen by convention. Reference: Hart D. P. (2000) 'PIV error correction',{ Exp. Fluids} '''29''', 13-22. |
| | 827 | *vec_F(i)=3: the optimisation of the correlation function is unstable or local Intensity rms of the image =0 |
| | 828 | *vec_F(i)=4:only in civ2: the difference between the estimator and the result is more than 1 pixel. The two criteria, vec_F(i)=-2, and 3, should be selected (default options). The criterium vec_F=2 (Hart) should not be selected, while vec_F=4 (for civ2) could be selected only for excellent data (otherwise it may be too strict). -''' {Threshold on the image correlation} ''' (vec_C) can be introduced by the edit box [thresh_vecC] (value between 0 and 1). It removes vectors with poor correlation. -''' {Threshold on the velocity modulus } ''' (expressed in pixels): it can remove either too small values (menu '''[inf_sup1]''' set to '<'), or excessive values (menu '''[inf_sup1]''' set to '>'). Erratic zero velocity vectors, produced by a fixed image background, can be eliminated by this criterium. These criteria can be as well applied to the difference with a reference field, defined by a file series (edit box '''[ref_fix1]''') and a field inside the file (menu '''[field_ref1]'''). -''' {Mask fix:} ''' It has the same effect as the one used in civ1, but the removed vectors are kept in memory, labelled as false. -''' {Manual fix:} ''' Interactive fixing with the mouse is also possible, see [section 4.2->#4.2]. |
| | 829 | |
| | 830 | ''' {Code for FixFlag:} ''' |
| | 831 | *FixFlag(i)=0 :default, everything is fine |
| | 832 | *FixFlag(i)=1. : value 1 for the second digit: vector removed by criteria on vec_F or/and low correlation value |
| | 833 | *FixFlag(i)=1..: value 1 for the third digit: vector selected by a criterium of difference with another field, for instance filter, or a field with differnt time interval. |
| | 834 | *FixFlag(i)=...1, 2, 3 different criteria for elimination set by the program Fix of CIVx (not yet documented). |
