Georeference Tiepoints editor

Transformation

 

When editing a georeference tiepoints, select the transformation method with which the relation between Row and Column values and the XY-coordinates of your tiepoints should be calculated.

Dialog box options:

Select one of the transformation methods:

 

Conformal:

Plane, minimum of 2 tiepoints required;

Xout = aX + bY + c1

Yout = bX - aY + c2

Affine:

Plane; recommended; minimum of 3 tiepoints required;

Xout = a11X + a12Y + b1

Yout = a12X + a22Y + b2

Second order bilinear:

Second degree linear surface; minimum of 4 tiepoints required;

Xout = a1 + b1X + c1Y + d1XY

Yout = a2 + b2X + c2Y + d2XY

Full second order:

Full second degree polynomial surface; minimum of 6 tiepoints required;

Xout = a1 + b1X + c1Y + d1XY + e1X2 + f1Y2

Yout = a2 + b2X + c2Y + d2XY + e2X2 + f2Y2

Third order:

Third degree polynomial surface; minimum of 10 tiepoints required;

Xout = a1 + b1X + c1Y + d1XY + e1X2 + f1Y2 + g1 X3 + h1 X2Y + i1XY2 + j1 Y3

Yout = a2 + b2X + c2Y + d2XY + e2X2 + f2Y2 + g2 X3 + h2 X2Y + i2XY2 + j2 Y3

Projective:

Recommended for oblique vector maps; minimum of 4 tiepoints required;

Xout = (aX + bY + c) / (gX + hY +1)

Yout = (dX + eY + f) / (gX + hY + 1)

The transformation method and calculated sigma are visible at the top of the tiepoints table.

Tip:

For each transformation method, a certain number of tiepoints is mathematically required. It is advised to always add more tiepoints than the absolute minimum number required.

See also: