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Transform a feature

In the Modify Features pane, Transform Transform applies a geometric transformation to features using control points you create as two-point links in the map. The result is a best-fit transformation between the links. You can transform features that are visible and editable, including datasets that have no internal coordinate system such as CAD drawings or raster images.

When you create a link, the best practice is to snap the origin point to an edge or a vertex on the feature you are transforming and snap the destination point to the corresponding edge or vertex on the destination feature. By default, all links are automatically drawn on the Links layer. The required number of links depends on the transformation method.

Affine transformation

To perform an affine transformation, click Transform Transform, choose Affine, and select the feature. Create at least three links, and click Transform. Features are scaled, rotated, translated, reflected, and skewed. Angles and lengths are not preserved. Straight lines and ratios between distances along a straight line are preserved, and parallel lines remain parallel.

  1. On the Edit tab in the Features group, click Modify Modify Features.

    The Modify Features pane appears.

  2. Expand Alignment and click Transform Transform.

    The tool opens in the pane.

  3. Click the Selected features tab, click Select Select, and select the feature you want to transform.
    • To select all features on a layer, click the Layers tab, and select the layer.
  4. On the Edit tab in the Snapping group, enable your snapping preferences.
    • Press and hold the Spacebar to temporarily turn snapping off.
  5. Click the Transformation Method drop-down arrow, and click Affine.
  6. Click Add new links New Displacement Link, click the origin point on the map, and click the destination point.
    • Create at least three links.

    The RMS error displays at the top of the pane.

  7. To delete one or more links, do the following:
    • Click Select Select, select the link, and press the Delete key or right-click and click Delete on the context menu.
    • In the pane, click Delete all links Delete.
  8. Click Transform.

    The position, size, and orientation of the selected features are transformed.

Affine equation

x’ = Ax + By + C
y’ = Dx + Ey + F

where:

A = Sx cos rB = (Sy / cos s) sin(s - r)
C = DxD = Sx sin rE = (Sy / cos s) cos(s - r)
F = DySx, Sy = Scaling factors (can be negative)
Dx, Dy = Translation distances in x and y directions (can be negative)
s = Skew angle of shearing along x-axis, measured from y-axis (-pi/2 < s < pi/2)
r = Rotation angle in radians, measured counterclockwise from x-axis (- pi < r <= pi)

Similarity transformation

To perform a similarity transformation, click Transform Transform, choose Similarity, and select the feature. Create at least two links, and click Transform. Features are scaled uniformly, rotated, translated, and reflected. The relative shape of the feature is preserved, making this a good choice for CAD drawings and other file based data that should be skewed. Straight lines and ratios between distances along a straight line remain unchanged, and parallel lines remain parallel.

  1. On the Edit tab in the Features group, click Modify Modify Features.

    The Modify Features pane appears.

  2. Expand Alignment and click Transform Transform.

    The tool opens in the pane.

  3. Click the Selected features tab, click Select Select, and select the feature you want to transform.
    • To select all features on a layer, click the Layers tab, and select the layer.
  4. On the Edit tab in the Snapping group, enable your snapping preferences.
    • Press and hold the Spacebar to temporarily turn snapping off.
  5. Click the Transformation Method drop-down arrow, and click Similarity.
  6. Click Add new links New Displacement Link, click the origin point on the map, and click the destination point.
    • Create at least two links.

    The RMS error displays at the top of the pane.

  7. To delete one or more links, do the following:
    • Click Select Select, select the link, and press the Delete key or right-click and click Delete on the context menu.
    • In the pane, click Delete all links Delete.
  8. Click Transform.

    The position, size, and orientation of the selected features are transformed.

Similarity equation

x' = Ax + By + Cy' = -Bx + Ay + F

where:

A = s * cos tB = s * sin tC = Translation in x direction
F = Translation in y direction
s = Scale change (same in x and y directions)
t = Rotation angle, measured counterclockwise from the x-axis

Transformation links and the RMS error

Transformation links define a from-to order that scale, rotate, translate, and in some cases skew, the selected features to fit the destination control points.

Transformations

Each link generates a residual error that measures the fit between the location of the destination control point and the actual transformed location.

Residual errors

The root mean square (RMS) error that displays in the pane is a calculation of the sum of residual errors generated by each link.

RMS equation

The RMS error reports the overall fitness of a transformation. In general terms, a high RMS error value indicates that the source control points and their transformed locations do not correspond to the same relative locations. RMS errors vary depending on the accuracy of the original data and the scale of the source map.

Note:

In some cases, a high RMS error can indicate that a large amount of stretching or skewing of your data has occurred. Your particular requirements ultimately determine what an acceptable RMS error is. When an RMS error is determined to be too high, you can adjust the error by removing links and adding new control points.