Transformations between view and model coordinates
An important aspect of working with an ILcdGXYView
is the ability to transform between view coordinates and model coordinates.
For an introduction of the coordinate systems that are used internally by an 
This article describes in more detail how to transform view coordinates to model coordinates. A typical application of such a transformation is to find out which objects in a model are located under the mouse cursor. The cursor position is defined in view coordinates, and to find the corresponding domain objects, the application needs to transform the cursor’s position to model coordinates.
This transformation happens in two steps:

The first step is a transformation from view coordinates to world coordinates. This step is performed using an
ILcdGXYViewXYWorldTransformation
. 
The second step is to transform the world coordinates to model coordinates, using an
ILcdModelXYWorldTransformation
.
The most convenient way to obtain the appropriate transformation classes is through an ILcdGXYContext
. An ILcdGXYContext
is typically used by painters and editors, as described in Painting and editing domain objects in a GXY view.
In other situations, the class TLcdGXYContext
can be used to construct a context manually. TLcdGXYContext
must be provided with an ILcdGXYView
and an ILcdGXYLayer
. The context then provides immediate access to the transformations needed.
From view coordinates to world coordinates
To go from view to world coordinates, the ILcdGXYViewXYWorldTransformation
is obtained from the ILcdGXYContext
. You can then use either viewAWTPoint2worldSFCT()
or viewXYPoint2worldSFCT()
to transform from view coordinates to world coordinates. The former method
requires a Point
as input, the latter requires an ILcdPoint
. Both methods store the transformed result in a side effect parameter. Note that this parameter should be of type TLcdXYPoint
rather than TLcdLonLatPoint
, as the latter cannot represent coordinates with the large range that is usually required for world coordinates.
Note that the methods mentioned above operate on points. Equivalent methods enable you to transform bounding boxes: ILcdGXYViewXYWorldTransformation
has methods viewAWTBounds2worldSFCT()
and viewXYBounds2worldSFCT()
From world coordinates to model coordinates
Given the world coordinates, you can now obtain the ILcdModelXYWorldTransformation
from the ILcdGXYContext
and continue with the transformation to model coordinates. This is done using the worldPoint2modelSFCT()
method. The SFCT model point in this method should be an ILcdPoint
that can be used in the reference of the model to which you are transforming, a TLcdLonLatHeightPoint
for geodetic references or a TLcdXYZPoint
for other references.
Note that the methods mentioned above operate on points. An equivalent method enables you to transform bounding boxes: ILcdModelXYWorldTransformation
has a method worldBounds2modelSFCT()
From model coordinates to view coordinates
The methods discussed in the previous sections have counterparts that work in the opposite direction, which allows for the
transformation from model coordinates to view coordinates. Be aware however that an ILcdBounds
may be enlarged as a result of the transformation. Therefore, transforming a bounding box from view to model coordinates
and back may produce a result that differs significantly from the input.
Program: Transforming a bounding box from view to model coordinates, taken from samples.gxy.transformation
, shows how to transform an ILcdBounds
from view to model coordinates.
samples/gxy/transformation/mouseToGeodetic/TransformCoordinatesController
)
/**
* Computes a bounding box in model coordinates that corresponds to the given
* rectangle in view coordinates.
*
* @param aViewBounds The rectangle in view coordinates (pixels)
* @param aView the ILcdGXYView on which the rectangle is located
* @param aLayer the ILcdGXYLayer for whose model we're computing the bounds
* @return an ILcdBounds in model coordinates
* @throws TLcdOutOfBoundsException
* if the world to model transformation is unsuccessful
*/
private ILcdBounds getModelBoundsForViewBounds(
Rectangle aViewBounds,
ILcdGXYView aView,
ILcdGXYLayer aLayer
) throws TLcdOutOfBoundsException {
// The (2D) world coordinate system works with XY coordinates.
TLcdXYBounds worldBounds = new TLcdXYBounds();
// The model coordinate system isn't known. The model reference helps
// to create compatible bounds (e.g. XY or LonLat).
ILcdPoint modelPoint = aLayer.getModel().getModelReference().makeModelPoint();
ILcd3DEditableBounds modelBounds = modelPoint.getBounds().cloneAs3DEditableBounds();
// We use TLcdGXYContext to easily obtain the appropriate transformations.
TLcdGXYContext context = new TLcdGXYContext(aView, aLayer);
// Transform from view to world and from world to model coordinates.
// Various other methods are available on the transformations, for example to transform
// just points.
context.getGXYViewXYWorldTransformation().viewAWTBounds2worldSFCT(aViewBounds, worldBounds);
context.getModelXYWorldTransformation().worldBounds2modelSFCT(worldBounds, modelBounds);
return modelBounds;
}