Class LinearTransformBuilder
LinearTransformBuilder(int...)
constructor will be more efficient.
Otherwise a builder created by the LinearTransformBuilder()
constructor will be able to handle
randomly distributed coordinates.
Builders are not threadsafe. Builders can be used only once;
points cannot be added or modified after create(MathTransformFactory)
has been invoked.
The transform coefficients are determined using a least squares estimation method,
with the assumption that source positions are exact and all the uncertainty is in the target positions.
Linearizers
Consider the following situation (commonly found with netCDF files): the sources coordinates are pixel indices and the targets are (longitude, latitude) coordinates, but we suspect that the sources to targets transform is some undetermined map projection, maybe Mercator. A linear approximation between those coordinates will give poor results; the results would be much better if all (longitude, latitude) coordinates were converted to the right projection first. However, that map projection may not be known, but we can try to guess it by trialsanderrors using a set of plausible projections. That set can be specified byaddLinearizers(Map, int...)
.
If the create(MathTransformFactory)
method finds that one of the specified projections seems a good fit,
it will automatically convert all target coordinates to that projection.
That selected projection is given by linearizer()
. Since:
 0.5
 See Also:

Constructor Summary
ConstructorDescriptionCreates a new linear transform builder for randomly distributed positions.LinearTransformBuilder
(int... gridSize) Creates a new linear transform builder for source positions distributed on a regular grid. 
Method Summary
Modifier and TypeMethodDescriptionvoid
addLinearizers
(Map<String, MathTransform> projections, int... projToGrid) Adds transforms to potentially apply on target control points before to compute the linear transform.static LinearTransform
approximate
(MathTransform gridToCRS, Envelope domain) Returns a linear approximation of the given transform for the specified domain.double[]
Returns the Pearson correlation coefficients of the transform created bycreate(…)
.create
(MathTransformFactory factory) Creates a linear transform approximation from the source positions to the target positions.double[]
getControlPoint
(int[] source) Returns a single target coordinate for the given source coordinate, ornull
if none.Returns all control points as a map.int
Returns the number of dimensions in source positions.Returns the envelope of source points (keys of the map returned bygetControlPoints()
).int
Returns the number of dimensions in target positions.Returns the envelope of target points (values of the map returned bygetControlPoints()
).If target coordinates have been projected to another space, returns that projection.void
setControlPoint
(int[] source, double[] target) Sets a single matching control point pair.void
setControlPoints
(Map<? extends Position, ? extends Position> sourceToTarget) Sets all control point (source, target) pairs, overwriting any previous setting.void
setControlPoints
(MathTransform gridToCRS) Sets all control point (source, target) pairs, overwriting any previous setting.Returns a string representation of this builder for debugging purpose.

Constructor Details

LinearTransformBuilder
public LinearTransformBuilder()Creates a new linear transform builder for randomly distributed positions.Performance note
If the source coordinates are grid indices, then theLinearTransformBuilder(int...)
constructor will create a more efficient builder. 
LinearTransformBuilder
public LinearTransformBuilder(int... gridSize) Creates a new linear transform builder for source positions distributed on a regular grid. This constructor notifiesLinearTransformBuilder
that coordinate values of all source positions will be integers in the [0 …gridSize[0]
1] range for the first dimension (typically column indices), in the [0 …gridSize[1]
1] range for the second dimension (typically row indices), etc. The dimension of all source positions is the length of the givengridSize
array.An empty array is equivalent to invoking the noargument constructor, i.e. no restriction is put on the source coordinates.
 Parameters:
gridSize
 the number of integer coordinate values in each grid dimension. Throws:
IllegalArgumentException
 if a grid size is not strictly positive, or if the product of all values (∏gridSize
) is greater thanInteger.MAX_VALUE
. Since:
 0.8


Method Details

approximate
public static LinearTransform approximate(MathTransform gridToCRS, Envelope domain) throws FactoryException Returns a linear approximation of the given transform for the specified domain. The source positions are integer coordinates included in the given envelope. The target positions are the results of transforming source coordinates with the givengridToCRS
transform. Parameters:
gridToCRS
 the transform from source coordinates (grid indices) to target coordinates.domain
 domain of integer source coordinates for which to get a linear approximation. Returns:
 a linear approximation of given transform for the specified domain.
 Throws:
FactoryException
 if the transform approximation cannot be computed. Since:
 1.1
 See Also:

getSourceDimensions
public int getSourceDimensions()Returns the number of dimensions in source positions. This is the length of thesource
array given in argument toget
/setControlPoint(int[], …)
methods. This is also the number of dimensions of theDirectPosition
keys in theMap
exchanged byget
/setControlPoints(Map)
methods. Returns:
 the dimension of source points.
 Throws:
IllegalStateException
 if the number of source dimensions is not yet known. Since:
 0.8
 See Also:

getTargetDimensions
public int getTargetDimensions()Returns the number of dimensions in target positions. This is the length of thetarget
array exchanged byget
/setControlPoint(…, double[])
methods. This is also the number of dimensions of theDirectPosition
values in theMap
exchanged byget
/setControlPoints(Map)
methods. Returns:
 the dimension of target points.
 Throws:
IllegalStateException
 if the number of target dimensions is not yet known. Since:
 0.8
 See Also:

getSourceEnvelope
Returns the envelope of source points (keys of the map returned bygetControlPoints()
). The number of dimensions is equal togetSourceDimensions()
. This method returns the known minimum and maximum values (inclusive) for each dimension, not expanded to encompass full cell surfaces. In other words, the returned envelope encompasses only cell centers.If a grid size was
specified at construction time
, then those minimums and maximums are inferred from the grid size and are always integer values. Otherwise, the minimums and maximums are extracted from the control points and may be any floating point values. In any cases, the lower and upper values are inclusive. Returns:
 the envelope of source points (cell centers), inclusive.
 Throws:
IllegalStateException
 if the source points are not yet known. Since:
 1.0

getTargetEnvelope
Returns the envelope of target points (values of the map returned bygetControlPoints()
). The number of dimensions is equal togetTargetDimensions()
. The lower and upper values are inclusive. If a linearizer has been applied, then coordinates of the returned envelope are projected by that linearizer. Returns:
 the envelope of target points.
 Throws:
IllegalStateException
 if the target points are not yet known. Since:
 1.0

setControlPoints
Sets all control point (source, target) pairs, overwriting any previous setting. The source positions are all integer coordinates in a rectangle from (0, 0, …) inclusive togridSize
exclusive wheregridSize
is anint[]
array specified at construction time. The target positions are the results of transforming all source coordinates with the givengridToCRS
transform. Parameters:
gridToCRS
 the transform from source coordinates (grid indices) to target coordinates. Throws:
TransformException
 if a coordinate value cannot be transformed. Since:
 1.1
 See Also:

setControlPoints
public void setControlPoints(Map<? extends Position, ? extends Position> sourceToTarget) throws MismatchedDimensionExceptionSets all control point (source, target) pairs, overwriting any previous setting. The source positions are the keys in given map, and the target positions are the associated values. The map should not contain two entries with the same source position. Coordinate reference systems are ignored. Null positions are silently ignored. Positions with NaN or infinite coordinates cause an exception to be thrown.All source positions shall have the same number of dimensions (the source dimension), and all target positions shall have the same number of dimensions (the target dimension). However, the source dimension does not need to be the same than the target dimension. Apache SIS currently supports only one or twodimensional source positions, together with arbitrary target dimension.
If this builder has been created with the
LinearTransformBuilder(int...)
constructor, then the coordinate values of all source positions shall be integers in the [0 …gridSize[0]
1] range for the first dimension (typically column indices), in the [0 …gridSize[1]
1] range for the second dimension (typically row indices), etc. This constraint does not apply for builders created with theLinearTransformBuilder()
constructor. Parameters:
sourceToTarget
 a map of source positions to target positions. Source positions are assumed precise and target positions are assumed uncertain. Throws:
IllegalStateException
 ifcreate(…)
has already been invoked.IllegalArgumentException
 if the given positions contain NaN or infinite coordinate values.IllegalArgumentException
 if this builder has been created for a grid but some source coordinates are not indices in that grid.MismatchedDimensionException
 if some positions do not have the expected number of dimensions. Since:
 0.8

getControlPoints
Returns all control points as a map. Values are source coordinates and keys are target coordinates. The map is unmodifiable and is guaranteed to contain only nonnull keys and values. The map is a view: changes in this builder are immediately reflected in the returned map.If
linearizer()
returns a nonempty value, then the values in the returned map are projected using that linearizer. This may happen only aftercreate(…)
has been invoked. Returns:
 all control points in this builder.
 Since:
 1.0

setControlPoint
public void setControlPoint(int[] source, double[] target) Sets a single matching control point pair. Source position is assumed precise and target position is assumed uncertain. If the given source position was already associated with another target position, then the old target position is discarded.Performance note
Current implementation is efficient for builders created for a grid but inefficient for builders created for randomly distributed points. In the latter case, thesetControlPoints(Map)
method is a more efficient alternative. Parameters:
source
 the source coordinates. If this builder has been created with theLinearTransformBuilder(int...)
constructor, then for every index i thesource[i]
value shall be in the [0 …gridSize[i]
1] range inclusive. If this builder has been created with theLinearTransformBuilder()
constructor, then no constraint apply.target
 the target coordinates, assumed uncertain. Throws:
IllegalStateException
 ifcreate(…)
has already been invoked.IllegalArgumentException
 if this builder has been created for a grid but some source coordinates are out of index range, or iftarget
contains NaN of infinite numbers.MismatchedDimensionException
 if the source or target position does not have the expected number of dimensions. Since:
 0.8

getControlPoint
public double[] getControlPoint(int[] source) Returns a single target coordinate for the given source coordinate, ornull
if none. This method can be used for retrieving points set by previous calls tosetControlPoint(int[], double[])
orsetControlPoints(Map)
.If
linearizer()
returns a nonempty value, then the returned values are projected using that linearizer. This may happen only if this method is invoked aftercreate(…)
.Performance note
Current implementation is efficient for builders created for a grid but inefficient for builders created for randomly distributed points. Parameters:
source
 the source coordinates. If this builder has been created with theLinearTransformBuilder(int...)
constructor, then for every index i thesource[i]
value shall be in the [0 …gridSize[i]
1] range inclusive. If this builder has been created with theLinearTransformBuilder()
constructor, then no constraint apply. Returns:
 the target coordinates associated to the given source, or
null
if none.  Throws:
IllegalArgumentException
 if this builder has been created for a grid but some source coordinates are out of index range.MismatchedDimensionException
 if the source position does not have the expected number of dimensions. Since:
 0.8

addLinearizers
Adds transforms to potentially apply on target control points before to compute the linear transform. This method can be invoked when the source to target transform would possibly be more linear if target was another space than the current one. If linearizers have been specified, then thecreate(MathTransformFactory)
method will try to apply each transform on target coordinates and check which one get the best correlation coefficients.Exactly one of the specified transforms will be selected. If applying no transform is an acceptable solution, then an identity transform should be included in the given
projections
map. The transform selected byLinearTransformBuilder
will be given bylinearizer()
.Linearizers are specified as a collection of
MathTransform
s from current target coordinates to some other spaces where sources to new targets transforms may be more linear. Keys in the map are arbitrary identifiers. Values in the map should be nonlinear transforms;LinearTransform
s (other than identity) should be avoided because they will consume processing power for no correlation improvement.Error handling
If aTransformException
occurred or if some transform results were NaN or infinite, then theMathTransform
that failed will be ignored. If all transforms fail, then aFactoryException
will be thrown by thecreate(…)
method.Dimensions mapping
TheprojToGrid
argument mapsprojections
dimensions to target dimensions of this builder. For example ifprojToGrid
array is{2,1}
, then coordinate values in target dimensions 2 and 1 of this grid will be used as source coordinates in dimensions 0 and 1 respectively for all given projections. Likewise, the projection results in dimensions 0 and 1 of all projections will be stored in target dimensions 2 and 1 respectively of this grid.The
projToGrid
argument can be omitted or null, in which case {0, 1, 2 …getTargetDimensions()
 1} is assumed. All givenprojections
shall have a number of source and target dimensions equals to the length of theprojToGrid
array. It is possible to invoke this method many times with differentprojToGrid
argument values. Parameters:
projections
 projections from current target coordinates to other spaces which may result in more linear transforms.projToGrid
 the target dimensions to project, or null or omitted for projecting all target dimensions in same order. Throws:
IllegalStateException
 ifcreate(…)
has already been invoked.MismatchedDimensionException
 if a projection does not have the expected number of dimensions. Since:
 1.0
 See Also:

create
Creates a linear transform approximation from the source positions to the target positions. This method assumes that source positions are precise and that all uncertainties are in target positions. If linearizers have been specified, then this method will project all target coordinates using one of those linearizers in order to get a more linear transform. If such projection is applied, thenlinearizer()
will return a nonempty value after this method call.If this method is invoked more than once, the previously created transform instance is returned.
 Specified by:
create
in classTransformBuilder
 Parameters:
factory
 the factory to use for creating the transform, ornull
for the default factory. TheMathTransformFactory.createAffineTransform(Matrix)
method of that factory shall returnLinearTransform
instances. Returns:
 the fitted linear transform.
 Throws:
FactoryException
 if the transform cannot be created, for example because the source or target points have not be specified. Since:
 0.8

linearizer
If target coordinates have been projected to another space, returns that projection. This method returns a nonempty value ifaddLinearizers(Map, int...)
has been invoked with a nonempty map, followed by acreate(MathTransformFactory)
call. In such case,LinearTransformBuilder
selects a linearizer identified by the returned key  value entry. The entry key is one of the keys of the maps given toaddLinearizers(…)
. The entry value is the associatedMathTransform
, possibly modified as described in the axis order section below.The envelope returned by
getTargetEnvelope()
and all control points returned bygetControlPoint(int[])
are projected by the selected transform. Consequently, if the target coordinates of original control points are desired, then the transform returned bycreate(…)
needs to be concatenated with the inverse of the transform returned by thislinearizer()
method.Axis order
The source coordinates expected by the returned transform are the control points target coordinates. The returned transform will contain an operation step performing axis filtering and swapping implied by theprojToGrid
argument that was given to theaddLinearizers(…, projToGrid)}
method. Consequently, if theprojToGrid
argument was not an arithmetic progression, then the transform returned by this method will not be one of the instances given toaddLinearizers(…)
. Returns:
 the projection applied on target coordinates before to compute a linear transform.
 Since:
 1.1

correlation
public double[] correlation()Returns the Pearson correlation coefficients of the transform created bycreate(…)
. The closer those coefficients are to +1 or 1, the better the fit. This method returnsnull
ifcreate(…)
has not yet been invoked. If nonnull, the array length is equal to the number of target dimensions. Returns:
 estimation of Pearson correlation coefficients for each target dimension,
or
null
ifcreate(…)
has not been invoked yet.

toString
Returns a string representation of this builder for debugging purpose. Current implementation shows the following information: Number of points.
 Linearizers and their correlation coefficients (if available).
 The linear transform (if already computed).
