20 | | The parameter '''[num_!CorrSmooth]''' is used to fit the correlation data with a Gaussian function to obtain the maximum with sub-pixel precision. We generally keep the default value 1, while the value 2 should be more appropriate for larger particles (with wider correlation maximum). The quality of this feature can be tested by taking the image autocorrelation, selecting the option 'displacement' instead of 'PIV' in the menu '''[!ListCompareMode]''' of '''civ_input'''. Then run the '''[CIV1]''' computation with '''series'''. Visualise the velocity field with uvmat: it is very close to 0 as expected but the histogram of the error can be estimated with the Tool/rectangle. The curve exported from '''view_field''' is shown in figure below**, comparing '''[!CorrSmooth]'''=1 and 2'''. '''We see that the histogram is somewhat more narrow for '''[!CorrSmooth]'''=1, corresponding to a slightly better result, but the typical error of the order of 0.1 px in both cases. |
| 20 | The parameter '''[num_!CorrSmooth]''' is used to fit the correlation data with a Gaussian function to obtain the maximum with sub-pixel precision. We generally keep the default value 1, while the value 2 should be more appropriate for larger particles (with wider correlation maximum). The quality of this feature can be tested by taking the image autocorrelation, selecting the option 'displacement' instead of 'PIV' in the menu '''[!ListCompareMode]''' of '''civ_input'''. Then run the '''[CIV1]''' computation with '''series'''. Visualise the velocity field with uvmat: it is very close to 0 as expected but the histogram of the error can be estimated with the Tool/rectangle. The curve exported from '''view_field''' is shown in figure below, comparing '''[!CorrSmooth]'''=1 and 2'''. '''We see that the histogram is somewhat more narrow for '''[!CorrSmooth]'''=1, corresponding to a slightly better result, but the typical error of the order of 0.1 px in both cases. |
| 21 | |
| 22 | [[Image(Tutorial6 - Corr1vs2.png)]] |