VectorField (vf) Resources

vfCopyData

The boolean resource vfCopyData allows you to control whether the VectorField object always copies the elements of the vfDataArray into a private memory area. If you set vfCopyData False, VectorField will not copy the vfXArray or the vfYArray data and will try to avoid making a copy of the vfDataArray data. You are then responsible for ensuring that the data memory locations for these arrays are preserved intact for the lifetime of the VectorField. In return, you may save dynamic memory space. Note that a number of circumstances require VectorField to copy the data regardless. These include supplying data of any type other than NhlTFloat, requesting that the data dimensions be exchanged, or setting a stride value greater than 1 in either the X or the Y dimension. Also, if you specify a data array subset and one or both of the coordinate array resources (vfXArray and/or vfYArray) is non-NULL, copies are made of the subsetted part of the coordinate array.

Default: True

vfDataArray

This resource specifies a 3-dimensional array containing the data comprising a vector field. You must specify either vfDataArray or the two resources vfUDataArray and vfVDataArray in order to create a VectorField object. The slowest varying dimension (first dimension in C, third dimension in Fortran) must contain two elements, representing the two components of the field. The first element represents the U data and the second the V data (before the effect of vfExchangeUVData is taken into account). The fastest varying dimension represents the X Axis of the data coordinate system; vfXC... VectorField resources always relate to this dimension. The middle dimension represents the data coordinate Y Axis; vfYC... resources always relate to this dimension.

Although the VectorField object always converts the data into type NhlTFloat before passing them along to recipient objects, it accepts data arrays containing data of any of the following types:

• NhlTByte
• NhlTCharacter
• NhlTShort
• NhlTInteger
• NhlTLong
• NhlTFloat
• NhlTDouble

Default: NULL

vfExchangeDimensions

When this boolean resource is set True, VectorField exchanges the X and Y dimensions of the data before passing them to the recipient object. Resouces associated with the X-Axis are applied to the Y-Axis of the output data and vice-versa. This will have the effect of turning the plot on its side when rendered by a plot object. Note that since the U and V components implicitly exist in the coordinate system that is exchanged, these arrays must be exchanged at the same time in order maintain an equivalent relationship between the elements of the field. You can do this by inverting the value of the resource vfExchangeUVData.

Whenever vfExchangeDimensions is True, VectorField must copy the data, regardless of the setting of the vfCopyData resource.

Default: False

vfExchangeUVData

When this boolean resource is set True, VectorField exchanges the roles of the U and V arrays. If you supply the data using the single array resource vfDataArray, the two elements of the slowest varying dimension are traded. If vfExchangeDimensions is set True, you must invert the current value of vfExchangeUVData in order to preserve the current relationship of the elements of the vector field. If vfPolarData is set True, then this resource controls which array is used for the magnitude and which for the angular direction.

Default: False

vfMagMaxV

By default the VectorField object sets vfMagMaxV to the largest vector magnitude computed from the individual vector components in the data arrays. However, if you set the value of this resource, VectorField assumes that the set value is, in fact, the maximum magnitude. You may set vfMagMaxV using any of the data types VectorField accepts for the vfDataArray resource.

Default: <dynamic>

vfMagMinV

By default the VectorField object sets vfMagMinV to the smallest vector magnitude computed from the individual vector components in the data arrays. However, if you set the value of this resource, VectorField assumes that the set value is, in fact, the minimum magnitude. You may set vfMagMinV using any of the data types VectorField accepts for the vfDataArray resource.

Default: <dynamic>

vfMissingUValueV

If vfSingleMissingValue is False and you set vfMissingUValueV to a non-NULL value, VectorField treats occurrences of its value in the U data array as representing an undefined data point. If left unset, VectorField assumes that all values in the U data array are valid.

If vfSingleMissingValue is True and you set vfMissingUValueV to a non-NULL value, VectorField treats occurrences of its value in either the U or V data arrays as representing an undefined data point. If vfMissingUValueV is not set, but vfMissingVValueV is set, then occurrences of the value of vfMissingVValueV in either array causes the data point to be treated as undefined. If neither vfMissingUValueV nor vfMissingVValueV is set, then VectorField assumes that all values in the U data array are valid.

You may set vfMissingVValueV using any of the data types VectorField accepts for the vfDataArray resource.

Default: NULL

vfMissingVValueV

If vfSingleMissingValue is False and you set vfMissingVValueV to a non-NULL value, VectorField treats occurrences of its value in the V data array as representing an undefined value. If left unset, VectorField assumes that all values in the V data array are valid.

If vfSingleMissingValue is True and you set vfMissingVValueV to a non-NULL value, its value is ignored unless vfMissingUValueV is not set. If vfMissingUValueV is not set, VectorField treats occurrences of the value of vfMissingVValueV in either the U or V data arrays as representing an undefined data point. If neither vfMissingUValueV nor vfMissingVValueV is set, then VectorField assumes that all values in the U data array are valid.

You may set vfMissingVValueV using any of the data types VectorField accepts for the vfDataArray resource.

Default: NULL

vfPolarData

If this resource is set True, the arrays passed into VectorField are assumed to represent the vector field in terms of magnitude and angular direction rather than by orthogonal vector components. By default the U array is interpreted as the magnitude and the V array as direction. However, if the resource vfExchangeUVData is set True, the V array will be assumed to contain the magnitude and the U array the direction.

Default: False

vfSingleMissingValue

When this boolean resource is set True, VectorField assumes that any missing values in both the U and V arrays are represented by the same sentinel value. In this case, you need set only one of the resources vfMissingUValueV and vfMissingVValueV to indicate the sentinel missing value. If both are set, then the value given by vfMissingVValueV is ignored. When vfSingleMissingValue is set False, then the U and V array are examined separately for their individual missing values, as specified by the resources vfMissingUValueV and vfMissingVValueV.

Default: False

vfUDataArray

If vfDataArray is not set, then this resource and vfVDataArray must both be specified in order to create a VectorField object. Together, these resources specify the data defining a vector field using two arrays specifying the vector components. The fastest varying dimension (second dimension in C, first dimension in Fortran) represents the X Axis of the data coordinate system; vfXC... VectorField resources always relate to this dimension. The other dimension represents the data coordinate Y Axis; vfYC... resources always relate to this dimension.

You may set vfUDataArray using any of the data types VectorField accepts for the vfDataArray resource.

Default: NULL

vfUMaxV

By default the VectorField object sets vfUMaxV to the largest value in the U data array. However, if you set the value of this resource, VectorField does not process the array to find the maximum value. Instead it assumes that the set value is, in fact, the maximum value. You may set vfUMaxV using any of the data types VectorField accepts for the vfDataArray resource.

Default: <dynamic>

vfUMinV

By default the VectorField object sets vfUMinV to the smallest value in the U data array. However, if you set the value of this resource, VectorField does not process the array to find the minimum value. Instead it assumes that the set value is, in fact, the minimum value. You may set vfUMaxV using any of the data types VectorField accepts for the vfDataArray resource.

Default: <dynamic>

vfVDataArray

If vfDataArray is not set, then this resource and vfUDataArray must both be specified in order to create a VectorField object. Together, these resources specify the data defining a vector field using two arrays specifying the vector components. The fastest varying dimension (second dimension in C, first dimension in Fortran) represents the X Axis of the data coordinate system; vfXC... VectorField resources always relate to this dimension. The other dimension represents the data coordinate Y Axis; vfYC... resources always relate to this dimension.

You may set vfVDataArray using any of the data types VectorField accepts for the vfDataArray resource.

Default: NULL

vfVMaxV

By default the VectorField object sets vfVMaxV to the largest value in the V data array. However, if you set the value of this resource, VectorField does not process the array to find the maximum value. Instead it assumes that the set value is, in fact, the maximum value. You may set vfVMaxV using any of the data types VectorField accepts for the vfDataArray resource.

Default: <dynamic>

vfVMinV

By default the VectorField object sets vfVMinV to the smallest value in the V data array. However, if you set the value of this resource, VectorField does not process the array to find the minimum value. Instead it assumes that the set value is, in fact, the minimum value. You may set vfVMaxV using any of the data types VectorField accepts for the vfDataArray resource.

Default: <dynamic>

vfXArray

If vfXArray is NULL, the coordinates of the X (fastest-varying) axis of the data grid are assumed to be regularly spaced, and the endpoints are determined by the values of vfXCStartV and vfXCEndV.

If vfXArray is set using a 1D array, its values represent sequential coordinate locations along the X-Axis (the fastest-varying dimension) of the data grid. The array must contain the same number of elements as this data array dimension. VectorField requires the coordinate array values to increase or decrease monotonically. If the coordinate array input does not have the right number of elements or is non-monotonic, VectorField issues a warning and restores vfXArray to its previous, possibly NULL, value. If the input array is valid, VectorField replaces the current value of vfXCStartV with the value of the first element of vfXArray, and the current value of vfXCEndV with the value of the last element.

If vfXArray is set using a 2D array, it must have the same dimension sizes as vfYArray and the two fastest varying dimensions of the data grid. Each element specifies the location along the X-Axis of a single data grid cell center. For 2D coordinates, there is no requirement that the coordinates be monotonic. However, if the coordinates provided are not well-ordered as expected by the 2D-coordinate tranvformation routines, errors will occur when the Draw method is called. If the array does not contain valid dimension sizes, VectorField issues a warning restores vfXArray to its previous, possibly NULL, value.

You can specify vfXArray using a one or two dimensional array of any of the types allowed for vfDataArray.

V4.1 Status Note 1

Default: NULL

vfXCActualEndF

When an ending location for a subset of the data is specified using vfXCEndSubsetV, this location might well fall between two data points. VectorField selects an ending index for the array subset such that the requested location is included within the subset. Thus the subset array, as delivered to the receiving object, may represent a slightly larger area of the data coordinate space than requested. In this case, the read-only resource vfXCActualEndF is set to the value of the actual ending location of the data subset along the X Axis.

When subsets are not specified, or are specified using the array indexing resources, vfXCActualEndF has the same value as vfXCEndSubsetV.

Default: <dynamic>

vfXCActualStartF

When a starting location for a subset of the data is specified using vfXCStartSubsetV, this location might well fall between two data points. In this case, VectorField selects a beginning index for the array subset such that the requested location is included within the subset. Thus the subset array, as delivered to the receiving object, may represent a slightly larger area of the data coordinate space than requested. The read-only resource vfXCActualStartF is set to the value of the actual starting location of the data subset along the X Axis.

When subsets are not specified, or are specified using the array indexing resources, vfXCActualStartF has the same value as vfXCStartSubsetV.

Default: <dynamic>

vfXCEndIndex

This resource specifies the larger of two indexes along the X-Axis data dimension. Valid values range from one greater than the value of vfXCStartIndex to one less than the size of the dimension. It is one of four resources used to specify a rectangular subset of the data using array indexes. This is the only form of subsetting VectorField supports when vfXArray and vfYArray are set using 2D coordinate arrays,

Unless vfXArray is set with a 2D array, explicitly setting vfXCEndSubsetV overrides any value set for vfXCEndIndex and causes it to be set to the smallest array index value such that the requested data coordinate location is included within the subset. Otherwise, if you set vfXCEndIndex, vfXCEndSubsetV will be set based on its value.

vfXCEndIndex retains its value when the data array changes, unless the X-Axis dimension size also changes. In this case, assuming neither vfXCEndSubsetV nor vfXCEndIndex is explicitly set at the same time, vfXCEndIndex is set to the size of the X-Axis dimension minus one.

Default: <dynamic>

vfXCEndSubsetV

vfXCEndSubsetV specifies the ending location along the X Axis of a rectangular sub-array of the data. It should be set to a value within the data coordinate extent as established by the values of vfXCStartV and vfXCEndV. If it is outside the coordinate extent, VectorField issues a warning and sets it to the value of vfXCEndV. If the values of vfXCStartSubsetV and vfXCEndSubsetV are oppositely directed from the direction established by vfXCStartV and vfXCEndV, VectorField issues a warning and exchanges their values. When you do not explicitly set a value for vfXCEndSubsetV:

• at initialization or when the X-Axis dimension size changes, if vfXCEndIndex is not set, vfXCEndSubsetV takes the value of vfXCEndV;
• else if vfXCEndIndex is set, or there is a change to vfXCStartV, vfXCEndV, or vfXArray, vfXCEndSubsetV takes the data coordinate value indexed by the value of vfXCEndIndex;
• else vfXCEndSubsetV retains its current value.

Since the data grid consists of data located at discrete points, the location specified by vfXCEndSubsetV might well fall between two data points. In this case, VectorField selects an ending index for the array subset such that the requested location is included within the subset. Thus the subset array, as delivered to the receiving object, may represent a slightly larger area of the data coordinate space than requested. Get the value of the read-only resource vfXCActualEndF in order to find the exact end of the subset along the X Axis. You may set vfXCEndSubsetV using any of the data types that VectorField accepts for the vfDataArray resource.

If vfXArray is set with a valid 2D coordinate array, VectorField ignores any value set for vfXCEndSubsetV. If a subset has been set using the indexing resources, vfXCEndSubsetV is set to the maximum value found within the specified subset of vfXArray. Otherwise vfXCEndSubsetV is set to the same value as vfXCEndV.

Default: <dynamic>

vfXCEndV

Ordinarily, this resource specifies the location along the X Axis of the last element of the fast-varying dimension of the data.If the array resource vfXArray is NULL, you can set vfXCEndV to any value (presumably meaningful in the context of the your data). If vfXCStartV is greater than vfXCEndV, the direction of the data locations along the X Axis is opposite the direction of the positive X Axis. If vfXArray is NULL and vfXCEndV is not specified, VectorField sets vfXCEndV to the size of the fast-varying data dimension minus one. You may set vfXCEndV using any of the data types VectorField accepts for the vfDataArray resource.

If you set vfXArray with a valid 1D or 2D array, VectorField ignores any value set for vfXCEndV. If vfXArray is one-dimensional, vfXCEndV is set to the value of its last element. If vfXArray is two-dimensional, vfXCStartV is set to the maximum value found in all elements of the array. In this case, it could correspond to any element of the data array.

Default: <dynamic>

vfXCStartIndex

This resource specifies the smaller of two indexes along the X-Axis dimension. Valid values range from 0 to one less than the value of vfXCEndIndex. It is one of four resources used to specify a rectangular subset of the data using array indexes. This is the only form of subsetting VectorField supports when vfXArray and vfYArray are set using 2D coordinate arrays,

Unless vfXArray is set with a 2D array, explicitly setting vfXCStartSubsetV overrides any value set for vfXCStartIndex and causes it to be set to the largest array index value such that the requested data coordinate location is included within the subset. Otherwise, if you set vfXCStartIndex, vfXCStartSubsetV will be set based on its value.

vfXCStartIndex retains its value when the data array changes, unless the X-Axis dimension size also changes. In this case, assuming neither vfXCStartSubsetV nor vfXCStartIndex is explicitly set at the same time, vfXCStartIndex is set to 0.

Default: 0

vfXCStartSubsetV

vfXCStartSubsetV specifies the starting location along the X Axis of a rectangular sub-array of the data. vfXCStartSubsetV should be set to a value within the data coordinate extent as established by the values of vfXCStartV and vfXCEndV. If vfXCStartSubsetV is outside the coordinate extent, VectorField issues a warning and sets it to the value of vfXCStartV. If the values of vfXCStartSubsetV and vfXCEndSubsetV are oppositely directed from the direction established by vfXCStartV and vfXCEndV, VectorField issues a warning and exchanges their values. When you do not explicitly set a value for vfXCStartSubsetV:

• at initialization or when the X-Axis dimension size changes, if vfXCStartIndex is also not set, vfXCStartSubsetV takes the value of vfXCStartV;
• else if vfXCStartIndex is set, or there is a change to vfXCStartV, vfXCEndV, or vfXArray, vfXCStartSubsetV takes the data coordinate value indexed by the value of the vfXCStartIndex resource;
• else vfXCStartSubsetV retains its current value.

Since the data grid consists of data located at discrete points, the location specified by vfXCStartSubsetV might well fall between two data points. In this case, VectorField selects a beginning index for the array subset such that the requested location is included within the subset. Thus the subset array, as delivered to the receiving object, may represent a slightly larger area of the data coordinate space than requested. Get the value of the read-only resource vfXCActualStartF in order to find the exact start of the subset along the X Axis. You may set vfXCStartSubsetV using any of the data types that VectorField accepts for the vfDataArray resource.

If vfXArray is set with a valid 2D coordinate array, VectorField ignores any value set for vfXCStartSubsetV. If a subset has been set using the indexing resources, vfXCStartSubsetV is set to the minimum value found within the specified subset of vfXArray. Otherwise vfXCStartSubsetV is set to the same value as vfXCStartV.

Default: <dynamic>

vfXCStartV

Ordinarily, this resource specifies the location along the X Axis of the first element of the fast-varying dimension of the data. If the array resource vfXArray is NULL, you can set vfXCStartV to any value (presumably meaningful in the context of the your data). If vfXCStartV is greater than vfXCEndV, the direction of the data locations along the X Axis is opposite the direction of the positive X Axis. If vfXArray is NULL and vfXCStartV is not specified, VectorField sets vfXCStartV to the value 0. You may set vfXCStartV using any of the data types VectorField accepts for the vfDataArray resource.

If you set vfXArray with a valid 1D or 2D array, VectorField ignores any value set for vfXCStartV. If vfXArray is one-dimensional, vfXCStartV is set to the value of its first element. If vfXArray is two-dimensional, vfXCStartV is set to the minimum value found in all elements of the array. In this case, it could correspond to any element of the data array.

Default: <dynamic>

vfXCStride

When vfXCStride has a value greater than one, the VectorField object creates a new array containing only columns indexed along the X dimension by successive multiples (starting with 0) of the vfXCStride value added to the starting index. The starting index is based on the current state of the applicable subsetting resources; it is 0 if no array subsetting is in effect. The resulting array is passed to the receiving plot object.

Note that if ending index minus starting index is not an exact multiple of the vfXCStride value, then the data coordinate range may be reduced slightly.

The vfXCStride resource is currently ignored if vfXArray and vfYArray contain 2D coordinate arrays.

Default: 1

vfYArray

If vfYArray is NULL, the coordinates of the Y (the second fastest-varying) axis of the data grid are assumed to be regularly spaced, and the endpoints are determined by the values of vfYCStartV and vfYCEndV.

If vfYArray is set using a 1D array, its values represent sequential coordinate locations along the Y-Axis (the second fastest-varying dimension) of the data grid. The array must contain the same number of elements as this data array dimension. VectorField requires the coordinate array values to increase or decrease monotonically. If the coordinate array input does not have the right number of elements or is non-monotonic, VectorField issues a warning and restores vfYArray to its previous, possibly NULL, value. equally-spaced along the Y Axis between the current values of vfYCStartV and vfYCEndV. If the input array is valid, VectorField replaces the current value of vfYCStartV with the value of the first element of vfYArray, and the current value of vfYCEndV with the value of the last element.

If vfYArray is set using a 2D array, it must have the same dimension sizes as vfXArray and the two fastest varying dimensions of the data grid. Each element specifies the location along the Y-Axis of a single data grid cell center. For 2D coordinates, there is no requirement that the coordinates be monotonic. However, if the coordinates provided are not well-ordered as expected by the 2D-coordinate tranvformation routines, errors will occur when the Draw method is called. If the array does not contain valid dimension sizes, VectorField issues a warning restores vfYArray to its previous, possibly NULL, value.

You can specify vfYArray using a one or two dimensional array of any of the types allowed for vfDataArray.

V4.1 Status Note 1

Default: NULL

vfYCActualEndF

When an ending location for a subset of the data is specified using vfYCEndSubsetV, this location might well fall between two data points. In this case, VectorField selects an ending index for the array subset such that the requested location is included within the subset. Thus the subset array, as delivered to the receiving object, may represent a slightly larger area of the data coordinate space than requested. The read-only resource vfYCActualEndF is set to the value of the actual ending location of the data subset along the Y Axis.

When subsets are not specified, or are specified using the array indexing resources, vfYCActualEndF has the same value as vfYCEndSubsetV.

Default: <dynamic>

vfYCActualStartF

When a starting location for a subset of the data is specified using vfYCStartSubsetV, this location might well fall between two data points. In this case, VectorField selects a beginning index for the array subset such that the requested location is included within the subset. Thus the subset array, as delivered to the receiving object, may represent a slightly larger area of the data coordinate space than requested. The read-only resource vfYCActualStartF is set to the value of the actual starting location of the data subset along the Y Axis.

When subsets are not specified, or are specified using the array indexing resources, vfYCActualStartF has the same value as vfYCStartSubsetV.

Default: <dynamic>

vfYCEndIndex

This resource specifies the larger of two indexes along the Y-Axis data dimension. Valid values range from one greater than the value of vfYCStartIndex to one less than the size of the dimension. It is one of four resources used to specify a rectangular subset of the data using array indexes. This is the only form of subsetting VectorField supports when vfXArray and vfYArray are set using 2D coordinate arrays,

Unless vfYArray is set with a 2D array, explicitly setting vfYCEndSubsetV overrides any value set for vfYCEndIndex and causes it to be set to the smallest array index value such that the requested data coordinate location is included within the subset. Otherwise, if you set vfYCEndIndex, vfYCEndSubsetV will be set based on its value.

vfYCEndIndex retains its value when the data array changes, unless the Y-Axis dimension size also changes. In this case, assuming neither vfYCEndSubsetV nor vfYCEndIndex is explicitly set at the same time, vfYCEndIndex is set to the size of the Y-Axis dimension minus one.

Default: <dynamic>

vfYCEndSubsetV

vfYCEndSubsetV specifies the ending location along the Y Axis of a rectangular sub-array of the data. It should be set to a value within the data coordinate extent as established by the values of vfYCStartV and vfYCEndV. If it is outside the coordinate extent, VectorField issues a warning and sets it to the value of vfYCEndV. If the values of vfYCStartSubsetV and vfYCEndSubsetV are oppositely directed from the direction established by vfYCStartV and vfYCEndV, VectorField issues a warning and exchanges their values. When you do not explicitly set a value for vfYCEndSubsetV:

• at initialization or when the Y-Axis dimension size changes, if vfYCEndIndex is not set, vfYCEndSubsetV takes the value of vfYCEndV;
• else if vfYCEndIndex is set, or there is a change to vfYCStartV, vfYCEndV, or vfYArray, vfYCEndSubsetV takes the data coordinate value indexed by the value of vfYCEndIndex;
• else vfYCEndSubsetV retains its current value.

Since the data grid consists of data located at discrete points, the location specified by vfYCEndSubsetV might well fall between two data points. In this case, VectorField selects an ending index for the array subset such that the requested location is included within the subset. Thus the subset array, as delivered to the receiving object, may represent a slightly larger area of the data coordinate space than requested. Get the value of the read-only resource vfYCActualEndF in order to find the exact end of the subset along the Y Axis. You may set vfYCEndSubsetV using any of the data types that VectorField accepts for the vfDataArray resource.

If vfYArray is set with a valid 2D coordinate array, VectorField ignores any value set for vfYCEndSubsetV. If a subset has been set using the indexing resources, vfYCEndSubsetV is set to the maximum value found within the specified subset of vfYArray. Otherwise vfYCEndSubsetV is set to the same value as vfYCEndV.

Default: <dynamic>

vfYCEndV

Ordinarily, this resource specifies the location along the Y Axis of the last element along the slower-varying dimension of the data. If the array resource vfYArray is set and found to be valid, VectorField overwrites the current value of vfYCStartV, replacing it with the value of the last element of vfYArray. Otherwise, you can set vfYCStartV to any value (presumably meaningful in the context of the your data). If vfYCStartV is greater than vfYCEndV, the direction of the data locations along the Y Axis is opposite the direction of the positive Y Axis. If vfYArray is NULL or invalid and vfYCEndV is not specified, VectorField sets vfYCEndV to the size of the slower-varying data dimension minus one. You may set vfYCEndV using any of the data types VectorField accepts for the vfDataArray resource.

If you set vfXArray with a valid 1D or 2D array, VectorField ignores any value set for vfXCEndV. If vfXArray is one-dimensional, vfXCEndV is set to the value of its last element. If vfXArray is two-dimensional, vfXCStartV is set to the maximum value found in all elements of the array. In this case, it could correspond to any element of the data array.

Default: <dynamic>

vfYCStartIndex

This resource specifies the smaller of two indexes along the Y-Axis dimension. Valid values range from 0 to one less than the value of vfYCEndIndex. It is one of four resources used to specify a rectangular subset of the data using array indexes. This is the only form of subsetting VectorField supports when vfXArray and vfYArray are set using 2D coordinate arrays,

Unless vfYArray is set with a 2D array, explicitly setting vfYCStartSubsetV overrides any value set for vfYCStartIndex and causes it to be set to the largest array index value such that the requested data coordinate location is included within the subset. Otherwise, if you set vfYCStartIndex, vfYCStartSubsetV will be set based on its value.

vfYCStartIndex retains its value when the data array changes, unless the Y-Axis dimension size also changes. In this case, assuming neither vfYCStartSubsetV nor vfYCStartIndex is explicitly set at the same time, vfYCStartIndex is set to 0.

Default: 0

vfYCStartSubsetV

vfYCStartSubsetV specifies the starting location along the Y Axis of a rectangular sub-array of the data. It should be set to a value within the data coordinate extent as established by the values of vfYCStartV and vfYCEndV. If it is outside the coordinate extent, VectorField issues a warning and sets it to the value of vfYCStartV. If the values of vfYCStartSubsetV and vfYCEndSubsetV are oppositely directed from the direction established by vfYCStartV and vfYCEndV, VectorField issues a warning and exchanges their values. When you do not explicitly set a value for vfYCStartSubsetV:

• at initialization or when the Y-Axis dimension size changes, if vfYCStartIndex is not set, vfYCStartSubsetV takes the value of vfYCStartV;
• else if vfYCStartIndex is set, or there is a change to vfYCStartV, vfYCEndV, or vfYArray, vfYCStartSubsetV takes the data coordinate value indexed by the value of vfYCStartIndex;
• else vfYCStartSubsetV retains its current value.

Since the data grid consists of data located at discrete points, the location specified by vfYCStartSubsetV might well fall between two data points. In this case, VectorField selects a beginning index for the array subset such that the requested location is included within the subset. Thus the subset array, as delivered to the receiving object, may represent a slightly larger area of the data coordinate space than requested. Get the value of the read-only resource vfYCActualStartF in order to find the exact start of the subset along the Y Axis. You may set vfYCStartSubsetV using any of the data types that VectorField accepts for the vfDataArray resource.

If vfYArray is set with a valid 2D coordinate array, VectorField ignores any value set for vfYCStartSubsetV. If a subset has been set using the indexing resources, vfYCStartSubsetV is set to the mimimum value found within the specified subset of vfYArray. Otherwise vfYCStartSubsetV is set to the same value as vfYCStartV.

Default: <dynamic>

vfYCStartV

Ordinarily, this resource specifies the location along the Y Axis of the first element of the slow-varying dimension of the data. If the array resource vfYArray is NULL, you can set vfYCStartV to any value (presumably meaningful in the context of the your data). If vfYCStartV is greater than vfYCEndV, the direction of the data locations along the Y Axis is opposite the direction of the positive Y Axis. If vfYArray is NULL and vfYCStartV is not specified, VectorField sets vfYCStartV to the value 0. You may set vfYCStartV using any of the data types VectorField accepts for the vfDataArray resource.

If you set vfYArray with a valid 1D or 2D array, VectorField ignores any value set for vfYCStartV. If vfYArray is one-dimensional, vfYCStartV is set to the value of its first element. If vfYArray is two-dimensional, vfYCStartV is set to the minimum value found in all elements of the array. In this case, it could correspond to any element of the data array.

Default: <dynamic>

vfYCStride

When vfYCStride has a value greater than one, the VectorField object creates a new array containing only rows indexed along the Y dimension by successive multiples (starting with 0) of the vfYCStride value added to the starting index. The starting index is based on the current state of the applicable subsetting resources; it is 0 if no array subsetting in effect. The resulting array is passed to the receiving plot object.

Note that if ending index minus starting index is not an exact multiple of the vfYCStride value, then the data coordinate range may be reduced slightly.

The vfYCStride resource is currently ignored if vfXArray and vfYArray contain 2D coordinate arrays.

Default: 1