SGS 1633 REMOTE SENSING TECHNOLOGY 1

LAB REPORT 1

LECTURER :

PROF MOHD IBRAHIM SEENI MOHD

PREPARED BY:

MOHD FARID BIN FAUZI900707-03-5463

AG0900901-SGS 2009/10

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1.0 TITLEGeometric Correction

2.0 OBJECTIVES2.1 To correct the satellite data so that it is true to scale and

projection.2.2 To enhance the data in the correct position based on the real

place or map magnetic direction.2.3 Analysing all image resampling data using different method.

3.0 METHODOLOGY3.1 First, Click PCI Geomatica V9.1 program and select GCP Works.3.2 We have to select 4 different setups for GCP Works.

i. In Processing Requirements column, select Full Processing.ii. In Mathematical Model column, select Polynomial.

iii. In Source of GCP column, select User Entered Coordinates.iv. Click on accept button at last and the PCI GCP Works V9.1.0

window will be shown.3.3 Then in PCI GCPWorks V9.1.0 window,

i. Click on Select Uncorrected Image.

Figure 1: The uncorrected satellite imageii. Choose the uncorrected image which we need to correct.

iii. In the Database Channels, choose the best combination of channels which enable us to get a clear image.

iv. After select the channels, click Load & Close.3.4 Next, click on Define Goereferencing Units.

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i. Change Meter to Long/Lat.ii. Click on Earth Model button.

iii. Select D085 - Kertau 1948 [West Malaysia & Singapore] for Datum.

iv. Then select E012 – WGS 84 for ellipsoid.v. After select the datum and ellipsoid, click on accept button.

3.5 After that, click on Collect GCPs.i. Select a coordinate on the image and key in the coordinate

on the GCP menu.ii. Key in the Longitude and Latitude on that point and click on

Accept as GCP button to accept it as control point.iii. Repeat this 2 process for others coordinates until the last

coordinate.iv. Save and close the GCP after finished key in all coordinates.

GCPs LONGITUD

LATITUD

1 103˚36’29.86”

1˚39’40.81’’

2 103˚40’13.33”

1˚38’14.60’’

3 103˚39’09.58”

1˚36’19.20’’

4 103˚48’05.17”

1˚36’25.63’’

5 103˚48’53.37”

1˚34’13.05’’

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6 103˚54’46.03”

1˚33’16.16’’

7 103˚37’25.11”

1˚31’17.09’’

8 103˚39’33.76”

1˚32’53.71’’

9 103˚41’05.57”

1˚30’00.19’’

10 103˚43’05.50”

1˚29’29.86’’

11 103˚46’11.30”

1˚31’27.98’’

12 103˚49’14.46”

1˚31’15.59’’

13 103˚52’04.82”

1˚28’02.73’’

14 103˚35’29.15”

1˚26’51.13’’

15 103˚39’14.35”

1˚25’41.82

16 103˚46’05.28”

1˚27’26.27’’

17 103˚46’46.60”

1˚27’58.36’’

3.6 Then, click on Perform Registration to Disk to start the re-sampling of the image.

i. Click on New Output File and type a name for the file.ii. In New File Type Selector window, select PCIDSK(.pix) as file

format.iii. Under Number of Channels column, change to 7 Channels

with 8-bit signed.iv. Select Band Interleaved as Format Options.v. Under Geo-Referencing Information, change Use pixel/lines

and bounds to Used pixel/lines and resolution.vi. Change the pixel size to 0d00’01.000” for X and Y column.

vii. Click on Create.viii. Select Default and drag the Memory (MB) slide to 32.0.

ix. Click on Perform Registration button.x. Close all the related windows.

3.7 Lastly, on Geomatica Toolbar V9.1.0, select Image Works Configuration.

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i. Click Use Image File, select the new image file.ii. Under File Information, change the Y dimension to maximum

scale .iii. Change also Image Planes to 7.iv. Click Accept & Load to view the corrected image.

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4.0 RESULT

The above figure shown all Ground Control Points(GCPs) and the following figure below shows the coefficients which calculated using 1st Degree Polynomial.

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This is the coefficient that being calculated using 2nd Degree Polynomial.

Forwardx ‘ = -373990.1 +3528.7x +783.9292y -2.107199xy +0.8769021x2 +3.283271y2

y’ = 40196.67 -168.303x +3490.923y +0.4506205xy -1.572458x2 +2.07147y2

Backward:x = 103.5835 +0.0002637396x -4.143648e-005y +3.163749e-011xy -1.616482e-011x2 -6.710729e-011y2

y = -1.667018 +3.696235e-005x +0.0002774233y -2.649279e-011xy +2.662779e-011x2 -5.227675e-011y2

This is the coefficient that being calculated using 3rd Degree Polynomial.

Forward:x ‘ = -229743.1 +1485.46x +147592.2y -2842.357xy +0x2 -404.3998y2 +13.6907x2 y

+0.7899071xy2 +0.06887933x3 -70.67193y3

y’ = 36915.28 -320.471x -26997.54y +279.8739xy +0x2 -10428.3y2 +0.1489505x2 y

+101.1137xy2 +0.0019725x 3 +11.24569y3

Backward:x’ = 103.5835 +0.0002636583x -4.119007e-005y -1.000802e-010xy +7.989206e-011x2 -7.064835e-010y2

-1.413018e-013x2 y +4.411238e-013xy2 -6.844629e-015x3 +3.558562e-013y3

y’ = -1.667008 +3.697817e-005x +0.0002771613y +6.523898e-010xy -1.108128e-010x2 +2.803846e-010y

-1.611679e-013x2 y -6.387019e-013xy2 +7.149368e-014x3 -5.703968e-014y3

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After all the points have been entered, the image then corrected by 2nd degree polynomial and nearest interpolation. The figure below is the image overview after Geometrical Correction.

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This is the overview of the corrected image with bilinear interpolation and 2nd degree polynomial after Geometric Correction.

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The figure below is the image overview after Geometrical Correction by using 2nd degree polynomial and nearest interpolation.

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5.0 ANALYSING DATA

For this practical, the satellite image data from Landsat TM have been used. This data being used as to done Geometric Correction. This raw image is a distorted image. All images taken from satellite contain distortion and error. This distortion was cause by the perspective of the sensor optics; the motion of the scanning system; the motion of the platform; the platform altitude, attitude and velocity change; the terrain relief and the curvature and rotation of the earth. There many type of distortion such as radial distortion, tangential distortion, step-wise distortion, scale error, projection distortion, skew, along track scale error and scan line scale error. Geometric correction is done in order to achieve as close as possible between geometry representation of image and the real place on the earth. The first aspect that we should consider while doing this practical is to achieve a low Root Mean Square (RMS) error.

Refer to my report, I had achieve a RMS error of 2.90 and 2.77 for the coordinates X and Y respectively in First Degree Polynomial. While in the Second Degree Polynomial, the RMS error of coordinates X and Y are 0.71 and 0.92. Theoretically, the RMS error for Second Degree Polynomial should be less than First Degree Polynomial due to Second Degree Polynomial is used to achieve more accurate result. In professional use of the image, the particular image should contain RMS error less than 2.00 to give a precise analysis.

As to get better result, we must consider the points keyed-in the software. These GCPs should key in with well define and well distributed points in the image. The meaning of well define point is the location which will not be effect by any changes over a long time. The example of well define point is the road junction. The GCPs have to well distribute too on the image. Don’t put the all GCPs in nearest place or focus in certain place only. We must spread all the points to get the actual result.

The point that measured also must be exactly the same with the point on the ground. Make sure that the point is determined correctly. Do not ever put the point in different pixel if want to get better result. As prevention, zoom the image as large as there will not be a mistake done.

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Geometric correction was done by using polynomial function. This polynomial function is important to gain the corrected image as well as on the ground. We can use either 1st, 2nd, 3rd, 4th degree or so on but mostly people use 2nd and 3rd degree polynomials.

First Degree PolynomialX1 = a0 + a1x + a2y

Y1 = b0 + b1X + b2y

Second Degree Polynomial

X1 = a0 + a1x + a2y + a3xy + a4x2 + a5y2

Y1 = b0 +b1x + b2y + b3xy + b4x2 + b5y2

Third Degree Polynomial

X1 = a0 + a1x + a2y + a3xy + a4x2 + a5y2 + a6x2y + a7xy2 + a8x3 + a9y3

Y1 = b0 + b1x + b2y + b3xy + b4x2 + b5y2 + b6x2y + b7xy2 + b8x3 + b9y3

where:

X1,and Y1 are coordinate points from the corrected image,

x and y are coordinates from the original image.

First Degree Polynomial n ≥ 3Second Degree Polynomial n ≥ 6

Third Degree Polynomial n ≥ 10

3, 6 and 10 is the minimum GCPs that you should have if using 1st, 2nd

and 3rd degree polynomial but do not use exactly those number of GCPs because you may also get result (with no residual) but you cannot ensure whether your points are right or wrong.

1st degree polynomial is the simplest geometric correction. As we using higher degree of polynomials such as 2nd, 3rd, 4th, 5th and so on, we can get almost accurate result. But people always use whether 2nd

0r 3rd degree because it is most accurate than first degree and does not need more GCPs.

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The last part of geometric correction is resampling. This process is function as moving the pixel of the original image to the corrected image based on the algorithms above. This process will perform an image after the transformation. There are 3 types of resampling method named Nearest Neighbour, Bilinear Interpolation, and Cubic Convolution.

Method Technique Advantages DisadvantagesNearest Neighbour

Transfer of output pixel to the input pixel which nearest with it.

- Minimum lost of the extremes and subtleties of the image.- Fast computation.

- Resampling to smaller grid size.- “Stair stepped” effect occur around diagonal lines and curves.

Bilinear Interpolation

First-order interpolation between four adjacent input pixel.

- Spatially more accurate than nearest neighbour.- Result are smoother, without “stair stepped” effect that occur in nearest neighbour.

- Edges are smoothed and some extremes of the data file are lost.

Cubic Convolution

Cubic function based on 16 input pixel.

-Most accurate resampling method.- Effecting the image by sharpen the image and smooth out noise.

- Slow computation.- Most expensive method.

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This is the effect if we put GCPs wrongly. This is resampling image overview by bad distribution of GCPs.

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6.0 CONCLUSION6.1 Every image taken from satellite sensor has geometric error.6.2 Geometric correction done to make the image true to scale and

true in direction which exactly the same with the ground.6.3 We must put the GCPs point carefully to reduced the residual.6.4 We must have more than minimum GCPs for each degree

polynomial to prevent undefined residual or error.6.5 Resampling image must not folded.

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