Parent Topic: <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/GCPWORKS">GCPWORKS</a><hr>
<H3>Theory</H3>
GCPWorks only deals with non-systematic errors, which include those due
mostly to the variations in altitude and attitude (roll, pitch, and yaw)
of the sensor platform at the time the data was being acquired.
Measurement techniques to correct these errors involve the collection
of ground control points (GCPs) distributed evenly over the whole image.
The best GCPs are located at well-defined and easy to recognize points
on both the georeferenced (being registered to) and uncorrected (being registered)
data sets.  The displacements of these GCPs between the uncorrected and georeferenced
data sets are used in the correction of these errors.  A least squares
regression analysis is used to determine the coefficients for
two-coordinate transformation equations which relate the distorted image
to the desired true map projection.  The geometric correction is actually
carried out in a two-step process:
<P>
<UL>
<LI> Transformation of Pixel Coordinates:  Each pixel in the target (georeferenced)
image is transformed according to the warping polynomial
to determine a sampling location in the input (uncorrected) image.
</UL>
<UL>
<LI> Resampling:  Resampling is used to determine the pixel values to fill
into the georeferenced (output) image from the uncorrected (input) image.
</UL>
<ul>
<LI> <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/GCPWORKS|Theory|Polynomial+Transformations">Polynomial Transformations</a>
<ul>
<LI> <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/GCPWORKS|Theory|Polynomial+Transformations|Polynomial+Equations">Polynomial Equations</a>
<LI> <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/GCPWORKS|Theory|Polynomial+Transformations|Determining+the+Accuracy+of+the+Polynomial+Fit">Determining the Accuracy of the Polynomial Fit</a>
</ul>
<LI> <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/GCPWORKS|Theory|Thin+Plate+Spline">Thin Plate Spline</a>
<LI> <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/GCPWORKS|Theory|Satellite+Ortho+Model">Satellite Ortho Model</a>
<LI> <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/GCPWORKS|Theory|Resampling">Resampling</a>
<ul>
<LI> <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/GCPWORKS|Theory|Resampling|Nearest+Neighbour">Nearest Neighbour</a>
<LI> <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/GCPWORKS|Theory|Resampling|Bilinear+Interpolation">Bilinear Interpolation</a>
<LI> <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/GCPWORKS|Theory|Resampling|Cubic+Convolution">Cubic Convolution</a>
<LI> <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/GCPWORKS|Theory|Resampling|Sin(x)/x+8pt+and+16pt">Sin(x)/x 8pt and 16pt</a>
<LI> <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/GCPWORKS|Theory|Resampling|Resampling+Example">Resampling Example</a>
<ul>
<LI> <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/GCPWORKS|Theory|Resampling|Resampling+Example|Nearest+Neighbour">Nearest Neighbour</a>
<LI> <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/GCPWORKS|Theory|Resampling|Resampling+Example|Bilinear+Interpolation">Bilinear Interpolation</a>
<LI> <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/GCPWORKS|Theory|Resampling|Resampling+Example|Cubic+Convolution">Cubic Convolution</a>
</ul>
</ul>
<LI> <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/GCPWORKS|Theory|Mosaicking">Mosaicking</a>
<ul>
<LI> <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/GCPWORKS|Theory|Mosaicking|Mosaic+Cut+Line">Mosaic Cut Line</a>
<LI> <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/GCPWORKS|Theory|Mosaicking|Blending">Blending</a>
<LI> <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/GCPWORKS|Theory|Mosaicking|Colour+Balancing">Colour Balancing</a>
</ul>
<LI> <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/GCPWORKS|Theory|References">References</a>
</ul>
<hr>
Parent Topic: <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/GCPWORKS">GCPWORKS</a><br>
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