Polynomial Rectification

Rectification is the process of projecting the data onto a plane and making it conform to a map projection system.

Assigning map coordinates to the image data is called georeferencing.

Rectify a Landsat Image : Image to Image Rectification

You rectify a Landsat TM image of Atlanta, Georgia, using a georeferenced SPOT panchromatic image of the same area. The SPOT image is rectified to the State Plane map projection.

basic steps in rectifying the Landsat image

• display files
• start Geometric Correction Tool
• record GCPs
• compute a transformation matrix
• resample the image
• verify the rectification process

• Display tmAtlanta.img in Gray Scale of Layer 2
• Start GCP tool - Raster : Panchromatic : Transform&Orthocorrect : Control Points
• In the "Select Geometric Model" dialog, select Polynomial and then click OK.
• Collect Reference Points From : select "Image Layer (New Viewer)" and then click OK
• Select panAtlanta.img and then OK
• Polynomial model Parameters : close
  
  
  Selecting GCPs : You should choose points that are easily identifiable in both images, such as road intersections and landmarks.
  
  
• In order to make GCP #1 easier to see, right-hold in the Color column to the right of GCP #1 in the GCP Tool CellArray and select the color Yellow.
• click the Create GCP icon and select a GCP in the Input viewer.
• click the Create GCP icon and select a GCP at the corresponding location in the Reference viewer.
• Digitize at least two more GCPs in each Viewer (on tmAtlanta.img in the first Viewer and panAtlanta.img in the second Viewer) by repeating
  the above steps. The GCPs you digitize should be spread out across the image to form a large triangle (that is, they should not form a line).

Calculate Transformation Matrix from GCPs

• The Auto Calculation function is enabled by default in the GCP Tool. The Auto Calculation function computes the transformation in real time as you edit the GCPs or change the selection in the CellArray.
• Click "Display Model Property" icon and click Transformation tab. : The transformation matrix contains the coefficients for transforming the reference coordinate system to the input coordinate system.
• you can move a GCP in the Viewer while watching the transformation coefficients and errors change at the top of the GCP Tool.

Digitize Check Points - checking the accuracy of your transformation.

• In the last row of the CellArray, right-hold in each of the two Color columns and select Magenta.
• Edit => Set Point Type => Check
• Edit => Point Matching
• Correlation Threshold to .8 , and then press the Enter key on your keyboard.
• Click the Discard Unmatched Point checkbox to activate it.
• In the GCP Tool, click the Create GCP icon and then the Lock icon. Create five check points in each of the two Viewers, just as you did for
  the GCPs.

Resample the Image

• Click the Resample icon in the Geo Correction Tools.
• under Output File, enter the name tmAtlanta_georef.img
• Under Resample Method, click the dropdown list and select Bilinear Interpolation.
• Click Ignore Zero in Stats
• Click OK

Verify the Rectification Process

• Display the resampled image (tmAtlanta_georef.img) in the first Viewer.
• Display the reference image (panAtlanta.img) in the second Viewer.
  
  or
  
• Display both the resampled image (tmAtlanta_georef.img) and the reference image (panAtlanta.img) in the same Viewer
• Start Swipe in the quick menus

% In class assignment, do the same procedure as above with polynomial orer of 2 .