| 605 | | -''' Recording calibration parameters: ''' Once the list of calibration points has been completed, press '''[APPLY]''', after selecting the appropriate option in '''[calib_type]''' (see the previous [#a8.1Generalities sub-section 8.1]). Note that the 3D options require a sufficient number of calibration points (typically > 10) spread over the image with different values of z, or a tilted grid, see below. Calibration coefficients are recorded in the XML file <!ImaDoc> associated with the image currently opened by UVMAT. If previous calibration data already exist, the previous XML file is updated, but the original one is preserved with the extension .xml~. If no XML file already exists, it is created. The image transformation to phys coordinates can be directly seen on the '''uvmat.fig''' interface after completion of the command '''[APPLY]'''. |
| 606 | | |
| 607 | | To reproduce the same calibrationn for image series, open one of the image in the series, and apply again the calibration with the same points, keeping the GUI geometry_calib opened. |
| 608 | | |
| 609 | | To calibrate at once a set of experiments, a better alternative is the command '''[REPLICATE]'''. Open a folder '''Campaign''', parent of the folders '''Experiment''' to treat. The GUI '''data_browser.fig''', also described in [#a3.7Dataorganisationinaproject section 3.7], then pops up. A two-column display appears, with the list of '''Experiments''' on the left and the list of corresponding '''[!DataSeries]''' on the right. Select the list of experiments to calibrate, and a single camera name in '''[!DataSeries]''', then validate by pressing '''[OK]'''. |
| 610 | | |
| 611 | | -''' 3D calibration''': 3D projection is handled by the options in '''[calib_type]''' '3D_lin' or '3D_quad' (if non-linear distortion is significant). By default, the set of calibration points is assumed to be contained in a single plane ''z''=0. For a correct determination of the 3D features, the normal to this plane must be tilted with respect to the line of view. Otherwise this problem of indetermination can be resolved by using a set of (typically 5-10) calibrations images using a plane grid with different tilting angles (for precision the grid must cover a large area of the view field). On each image, get calibration points with the tool '''[!Tools/Detect grid]''', introducing the appropriate grid mesh. Do not fill info on ''z'' coordinates. Store the points each time (without applying calibration at this stage), which fills the list [!ListCoordFiles] of file names. Then introduce a last grid image which will be considered as defining the orientation of the ''z'' axis, perpendicular to the grid. Detect points on this last image, but instead of storing them, apply the calibration with the option 3D_linear or 3D_quadr. A non-zero ''z'' position of this grid can be introduced by a z translation performed with '''[!Tools/Translate points]'''. It is generally convenient to do all these calibrations in air. Then transposition to water is done by the tool 'set_slice', see section 8.3. |
| | 605 | -''' 3D calibration''': 3D projection is handled by the options in '''[calib_type]''' '3D_lin','3D_quad' (if non-linear distortion is significant) or '3D_order4' (for strong distortion). Note that these 3D options require a sufficient number of calibration points (typically > 10) spread over the image with different values of z, or a tilted grid 9otherwise the algorithm may not converge). By default, the set of calibration points is assumed to be contained in a single plane ''z''=0. For a correct determination of the 3D features, the normal to this plane must be tilted with respect to the line of view. Otherwise this problem of indetermination can be resolved by using a few calibrations images using a plane grid with different tilting angles (for precision the grid must cover a large area of the view field). On each image, get calibration points with the tool '''[!Tools/Detect grid]''', introducing the appropriate grid mesh. Do not fill info on ''z'' coordinates. Store the points each time (without applying calibration at this stage), which fills the list [!ListCoordFiles] of file names. Then introduce a last grid image which will be considered as defining the orientation of the ''z'' axis, perpendicular to the grid. Detect points on this last image, but instead of storing them, apply the calibration with the option 3D_linear or 3D_quadr. A non-zero ''z'' position of this grid can be introduced by a z translation performed with '''[!Tools/Translate points]'''. It is generally convenient to do all these calibrations in air. Then transposition to water is done by the tool 'set_slice', see section 8.3. |
| | 618 | |
| | 619 | * Recording calibration parameters: ''' Once the calibration option and the list of calibration points have been obtained, press '''[APPLY]'''. Calibration coefficients are recorded in the XML file <!ImaDoc> associated with the image currently opened by UVMAT. If previous calibration data already exist, the previous XML file is updated, but the original one is preserved with the extension .xml~. If no XML file already exists, it is created. The image transformation to phys coordinates can be directly seen on the '''uvmat.fig''' interface after completion of the command '''[APPLY]'''. |
| | 620 | |
| | 621 | To reproduce the same calibration for another image series, open one of the image in the series, and apply again the calibration with the same points, keeping the GUI geometry_calib opened. |
| | 622 | |
| | 623 | To calibrate at once a set of experiments, a better alternative is to select the check box '''[REPLICATE]'''. Open a folder '''Campaign''', parent of the folders '''Experiment''' to treat. The GUI '''data_browser.fig''', also described in [#a3.7Dataorganisationinaproject section 3.7], then pops up. A two-column display appears, with the list of '''Experiments''' on the left and the list of corresponding '''[!DataSeries]''' on the right. Select the list of experiments to calibrate, and a single camera name in '''[!DataSeries]''', then validate by pressing '''[OK]'''. |
| | 624 | |
| | 625 | [[Image(browse_data_small.jpg)]] |
| 627 | 630 | Deducing the physical coordinates from image coordinates requires information on the illumination plane. The default assumption is that the objects in the image are in the plane used for calibration (assumed horizontal with x,y coordinates), but '''uvmat''' can handle volume scanning by a laser plane. A set of section planes can be defined by their origin positions and rotation angle vectors. Theses planes are labelled by a ''z index'', assumed to be the frame index j (case of volume scan), or the index i modulo the number of slices !NbSlice (case of 'multilevel' scan). These settings are stored in the xml file <!ImaDoc> as part of the section <Slice> and can be edited from '''uvmat.fig''' with the menu bar command '''[Tools/set slice]'''. A dialog box '''set_slices''' appears for entering the first and last section plane positions ''z'', as well as the number of slices and the option 'volume_scan' ('multilevel' otherwise). In the absence of 3D scan put twice the same value for first and last z. Finally a tilt angle of the laser sheet, around the ''x'' and ''y'' axis, can be introduced, with a possible angular scanning from first to last section planes. After introduction of the plane position information, the z-index is displayed in the frame '''[!FileIndices]''' of '''uvmat.fig'''. The local ''z'' position of the mouse pointer, assumed to lay on the current section plane, is then displayed in '''[text_display]'''. |
| 628 | 631 | |
| 629 | 632 | -''' Refraction effect:''' refraction effect can be accounted for if calibration was done in air by selecting the check box refraction, and introducing the water height (assumed at ''z''=cte) and refraction index. The apparent distance reduction for objects below the water height will be then taken into account. |
