Changes between Version 186 and Version 187 of UvmatHelp

Jan 28, 2015, 9:44:53 AM (6 years ago)



  • UvmatHelp

    v186 v187  
    852852'''PATCH1: ''' interpolates the velocity values on a regular grid with a smoothing parameter '''[num_!FieldSmooth]'''. This also provides the spatial derivatives (vorticity, divergence) needed for the refined processing civ2. The vectors which are too far from the smoothed field (erratic vectors) can be eliminated, using a threshold expressed in pixel displacement (set by '''[num_!MaxDiff]'''). The thin plate spline method must be done by subdomains for computational saving. The parameter [num_!SubDomain] gives the typical number of vectors used to determine the partition in subdomains. The default value 1000 fits the memory capacity of usual computers.
     854The button '''[TEST]''' in the '''[Patch]''' frame allows the user to witness the difference between the '''[Civ]''' and '''[Patch]''' correlations due to smoothing. It opens a graph in '''Figure1''' showing the difference between the two correlation according to the value of the '''[num_!FieldSmooth]''' parameter. This difference should be lower than 0.2 to not distort the results.
    854856=== 11.5 CIV2 ===
    855857- '''CIV2:''' provides a refined calculation of the velocity field, using the civ1 result as previous estimate. The civ1 field provides an estimated shift for each measurement point, so there is no edit box to enter shift parameter. The other parameters, in particular '''[!CorrBoxSize]''' and '''[!SearchBoxSize]''', have the same meaning as for Civ1. The image pair for civ2 ( set by the menu '''[!ListPairCiv2]''', can be different than the one used in civ1. It is generally advised to use a moderate time interval for civ1, to provide a first estimate avoiding false vectors, and to take a larger intervel for civ2, in order to optimize precision. As civ2 already knows where to look and takes into account image strain and rotation (with the option 'deformation') it allows for higher time intervals.
    862 - '''PATCH2:''' like '''[PATCH1]'''
     864- '''PATCH2:''' like '''[PATCH1]'''. Using the '''[TEST]''' option, we can here accept a difference between '''[Civ2]''' and '''[Patch2]''' higher than 0.2.
    864866Further iterations: improvements can be obtained by further iterations of the civ2-fix2-patch2 process. Open again the interface, and consider the previous civ2 result as the prior guess civ1. It will be recopied and relabelled as civ1 in the new NetCDF file produced.