ArcGIS Pro 2.8 API Reference Guide
Transform2D Method (IGeometryEngine)
Example 

ArcGIS.Core.Geometry Namespace > IGeometryEngine Interface : Transform2D Method
The array of coordinates to be transformed.
The projection transformation specifying the input and output spatial references and possibly the geographic transformations to use for the transformation.
The array of transformed coordinates. If it is null or the length is less than the length of inCoordinates, then a new array will be allocated.
(Optional) The boolean value specifying whether to remove clipped coordinates or not. If true, the coordinates outside of the horizon will be removed from the output array, and the number of initialized elements in the output array is the number of coordinates transformed which may be less than the number of elements in inCoordinates. If false, all coordinates are preserved, the clipped out coordinates are set to NaN in the output array, and the number of elements in the output array is equal to the number of elements in inCoordinates. The default value is false.
Transforms an array of 2D coordinates. Returns an array of transformed 2D coordinates.
Syntax

Parameters

inCoordinates
The array of coordinates to be transformed.
projectionTransformation
The projection transformation specifying the input and output spatial references and possibly the geographic transformations to use for the transformation.
outCoordinates
The array of transformed coordinates. If it is null or the length is less than the length of inCoordinates, then a new array will be allocated.
removeClippedCoordinates
(Optional) The boolean value specifying whether to remove clipped coordinates or not. If true, the coordinates outside of the horizon will be removed from the output array, and the number of initialized elements in the output array is the number of coordinates transformed which may be less than the number of elements in inCoordinates. If false, all coordinates are preserved, the clipped out coordinates are set to NaN in the output array, and the number of elements in the output array is equal to the number of elements in inCoordinates. The default value is false.

Return Value

The number of transformed coordinates.
Exceptions
ExceptionDescription
Input parameter, inCoordinates, is null.
ProjectionTransformation is null.
Remarks
This method should be applied to batches of coordinates for fast projection.
Example
// Not all of the input points are transformed as some of them are outside of the GCS horizon.
Coordinate2D[] inCoords2D = new Coordinate2D[]
{
  new Coordinate2D(-1, -1),
  new Coordinate2D(-2, -5),
  new Coordinate2D(-5, -11),
  new Coordinate2D(-10, -19),
  new Coordinate2D(-17, -29),
  new Coordinate2D(-26, -41),
  new Coordinate2D(-37, -5),
  new Coordinate2D(-50, -21),
  new Coordinate2D(-65, -39),
  new Coordinate2D(-82, -9)
};

int arraySize = inCoords2D.Length;

ProjectionTransformation projTrans = ProjectionTransformation.Create(SpatialReferences.WGS84, SpatialReferenceBuilder.CreateSpatialReference(24891));

Coordinate2D[] outCoords2D = new Coordinate2D[arraySize];

// transform and choose to remove the clipped coordinates
int numPointsTransformed = GeometryEngine.Instance.Transform2D(inCoords2D, projTrans, ref outCoords2D, true);

// numPointsTransformed = 4
// outCoords2D.Length = 4

// outCoords2D[0] = {5580417.6876455201, 1328841.2376554986}
// outCoords2D[1] = {3508774.290814558, -568027.23444226268}
// outCoords2D[2] = {1568096.0886155984, -2343435.4394415971}
// outCoords2D[3] = {57325.827391741652, 1095146.8917508761}

// transform and don't remove the clipped coordinates
numPointsTransformed = GeometryEngine.Instance.Transform2D(inCoords2D, projTrans, ref outCoords2D, false);

// numPointsTransformed = 4
// outCoords2D.Length = 10

// outCoords2D[0] = {double.Nan, double.Nan}
// outCoords2D[1] = {double.Nan, double.Nan}
// outCoords2D[2] = {double.Nan, double.Nan}
// outCoords2D[3] = {double.Nan, double.Nan}
// outCoords2D[4] = {double.Nan, double.Nan}
// outCoords2D[5] = {double.Nan, double.Nan}
// outCoords2D[6] = {5580417.6876455201, 1328841.2376554986}
// outCoords2D[7] = {3508774.290814558, -568027.23444226268}
// outCoords2D[8] = {1568096.0886155984, -2343435.4394415971}
// outCoords2D[9] = {57325.827391741652, 1095146.8917508761}
Requirements

Target Platforms: Windows 10, Windows 8.1

See Also

Reference

IGeometryEngine Interface
IGeometryEngine Members