Region gridding algorithms
When you export region inspection data, the data must be gridded for the volume data set file format.
The algorithms are described in the following sections:
The grid
All of the gridding algorithms begin by defining a grid of nodes in the X, Y, Z coordinate system of the platform at the time for the first ping which intersects the 3D region being gridded (if the platform is mobile it may move over the valid time of the 3D region). See About transducer geometry for further information.
This grid falls within a bounding box the dimensions of which are reported on the Statistics page of the Export Region Inspection Data dialog box. It is large enough to include all of the nodes which can influenced by the acoustic data samples within the region being gridded (that is, one node radius beyond the most extreme acoustic data sample in each of the X, Y and Z extremes).
This bounding box is subdivided into a number of nodes as specified on the General page of the Export Region Inspection Data dialog box
Intensity
The object of each gridding algorithm is to assign an intensity value to each of the nodes in the grid. This is a function of all of the acoustic data samples which fall within a sphere of influence of the node. The radius of the sphere of influence is defined on the Algorithm page of the Export Region Inspection Data dialog box.
The resulting intensities are scaled such that the fall within the range of 50 to 255, with the exception of No data values which are mapped to 0.
Algorithms
The following algorithm are available:
Unweighted mean
The intensity is equal to the average value of all the acoustic data sample values within the sphere of influence of that node.
Unweighted max
The intensity is equal to the maximum value of all the acoustic data sample values within the sphere of influence of that node.
Unweighted min
The intensity is equal to the minimum value of all the acoustic data sample values within the sphere of influence of that node.
Inverse distance algorithm
The intensity is equal to a weighted average of all the acoustic data sample values within the sphere of influence of that node. The weight is a function of the distance of each acoustic data sample from the node as follows:
where:
Fj = the intensity at node j fi = the value of the acoustic data sample i n = the number of acoustic data samples wi = a weight function for sample i as defined as:
where:
di = p = the Power parameter specified on the Algorithm page of the Export Region Inspection Data dialog box (xj , yj , zj) = coordinates of the node j (xi , yi , zi) = coordinates for acoustic data sample i
Note: The larger the value of p, the greater the bias in favor of near samples and away from more distant samples.
See also
About inspecting 3D regions
Exporting region inspection data
Viewing 3D objects outside Echoview
Viewing exported region inspection data
Volume data set file formats