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Geometric rectification

Homework 5

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Description Objective: geometrically rectify a portion (2km*2km) of SPOT image

over West Lafayette area Reference (GCP): to be measured from the USGS digital ortho quad

(DOQ). DOQ is used as the reference image Methodology: see the example Requirements:

at least 10 GCP and 6 check points need to be measured 10 meter spatial resolution for the rectified image Use and compare affine, polynomial (2nd order), projective transform

(2nd order) methods Data: ftp://ftp.ecn.purdue.edu/jshan/ce497URS/ Hand in: a report including (max. 3 pages, 12 font, 1.5 line spacing)

A brief description of the principles of the used methods Compare the results from different methods The rectified image with coordinate grid and scale info in Letter

format Show and discuss your selected GCP and their residuals Show and discuss your check points and their differences Discuss and summarize your findings

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Where to get help ? – pdf’s

FieldGuide: photogrammetry principles

TourGuide: step-by-step tutorial by modules

OrthBASE: orientation, matching, triangulation, DEM generation

StereoAnalyst: feature collection, stereo map compilation

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For the “geometric rect.” project, Read:

Field

Gu

ide: V

ol. 1

One-line manual :

TourGuide: step by step

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A worked example – tutorial

Landsat image is to be rectified

based on SPOT image, Atlanta

6

Choose one desired band to display

Image to be rectified – Landsat TM

To display only one band, use Raster > Band Combinations dialogue box as below

CE497 Urban Remote Sensing, Jie Shan

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Reference image – SPOT Pan

Load the SPOT Pan image in a separate viewer.

This image will be used as a reference image, i.e., any location on this image can be used as (2-D) ground control.

D:\IMAGINE\examples\panAtlanta.img

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Steps for geometric rectification

In the first view (the image to be rectified), run Raster > Geometric Correction command

Choose Polynomial in the Select Geometric Model dialogue box, select the polynomial order then click OK.

Click Close for now as below. (will make selection later)

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Steps for geometric rectification

Choose OK in the right window (Existing Viewer is checked)

At the following prompt, Click the second viewer (the oneto be used as reference). This steplet you choose the reference image.

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Steps for geometric rectification

Measure GCP. Note measure the 1st image (image to be rectified) first, and then the 2nd image (the reference image)

1st and 2nd polynomials can be tested. Rarely go beyond 2nd order. However, you can test what happens if so is chosen.

Measure a number of check points to evaluate the quality of rectification (set the point type from the “GCP Tool” menu: edit > set point type > check)

Analyze the error distribution and decide if more GCPs are needed and where.

Produce the image map using the resample tool. Check the on-line TourGuide for details.

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Options for Projective Transform Model

At least 9 GCPs are required to solve the 2D model (using the same denomination for x and y –default option-)

Choose “Projective Transform” in the “Set Geometric Model” dialogue box, select the RPC order, check “2D Dimension Projective Model” option and make sure that the “Use same denominator for x and y” option is checked.

Click Close