# Voxel value at a given depth of a mesh The `get.value.from.mesh` function is used to retrieve the values of an object of class "volume" at the desired depth of a surface described by a mesh. If the mesh corresponds to the "patient" contour, the zero depth is the skin, positive depths enter the patient and negative depths exit to the outside. ```r get.value.from.mesh( mesh, vol, method = c("point", "disk", "sphere"), depth = 0, radius = 5, spacing = 1, T.MAT = NULL, FUN = median, ... ) ``` ## Arguments - `mesh`: espadon "mesh" class object, or rgl/Rvcg "mesh3d" class object. "mesh3d" class object shall an additional field "ref.pseudo" specifying the mesh frame of reference. - `vol`: "volume" class object. - `method`: string specifying the desired method for retrieving measurements in `vol`. by default "point". Other methods exist, for example "disk" or "sphere. See details. - `depth`: Numeric value, representing the depth, relative to the surface of the mesh, at which values are retrieved. 0 corresponds to the surface, positive values enter the volume used to define the mesh and negative values leave it. - `radius`: Positive number, defining the radius of the disk or sphere, depending on the desired method. - `spacing`: spacing of the measurement points on the disk or sphere. - `T.MAT`: "t.mat" class object, created by load.patient.from.Rdcm , load.patient.from.dicom , load.T.MAT or ref.add . - `FUN`: function to be applied to reduce the data ("disk" or "sphere" method) to a single value. Default, median value. - `...`: Additional arguments passed to `FUN` if needed. ## Returns Returns a vector of values measured at the requested depth, with the desired method, filtered by `FUN`, at each vertex of the mesh. ## Details The `get.value.from.mesh` function works at each vertex of the mesh. It moves along the normal at that point to the desired depth. * When the method is "point", it simply retrieves the value of the volume `vol` specified at that point. * When the method is "disk", the values are retrieved on the disk orthogonal to the normal,with radius `radius`. * When the method is "sphere", the values are retrieved inside the sphere of radius `radius`. For "disk" or "sphere", the measurement points are spaced by `spacing`. For `radius=5` and `spacing=1`, "disk" and "sphere" perform 78 and 523 measurements respectively. In both cases, the measured values must be reduced to a single result using the `FUN` function. By default, espadon uses the median, but it can be provided with more complex functions to filter the data efficiently (see example below). ## Examples ```r # loading of toy-patient objects (decrease dxyz for better result) step <- 5 patient <- toy.load.patient (modality = c("ct", "rtstruct"), roi.name = "", dxyz = rep (step, 3)) CT <- patient$ct[[1]] S <- patient$rtstruct[[1]] # creation of the patient mesh bin <- bin.from.roi (CT, struct = S, roi.name = "patient", verbose = FALSE) mesh.patient <- mesh.from.bin (bin, alias = "patient", verbose = FALSE) # density value on the skin contour, extracted from CT density <- get.value.from.mesh (mesh.patient, CT ,depth = 0) if (interactive()){ # Display of mesh, with RVV pal density[density < -1000] <- -1000 density[density > 1000] <- 1000 col <- pal.RVV(255)[cut (density, seq (-1000, 1000, length.out = 256), include.lowest=TRUE)] rgl::open3d () display.3D.mesh (mesh.patient, col = col) } ```

get.value.from.mesh function