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Geography 228 > Section 5 > Flashcards

Section 5 Flashcards

1
Q

What are the two types of geometric correction?

A

Image to image

Image to map/vectors

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2
Q

What is an internal geometric error?

A

Errors introduced by the remote sensing scanner or with earths rotation.

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3
Q

What is another term for internal geometric error?

A

Systematic distortions.

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4
Q

What are the six types of systematic distortions?

A 
Scan skew
Mirror scan velocity
Panoramic distortion
Platform velocity
Earth rotation
Perspective
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5
Q

What are external geometric errors?

A

Movements by the aircraft like altitude change

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6
Q

Name and define the two types of external geometric errors

A

Altitude changes, attitude changes (roll pitch yaw)

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7
Q

What does changing altitude effect?

A

The scale of an image

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8
Q

What is more likely to have an attitude change, satellites or airplanes?

A

Airplanes

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9
Q

What is a way to prevent attitude distortions?

A

Gyro-stabilization equipment

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10
Q

What is the roll of a plane? And how will this effect an image?

A

Side to side rotation of a plane (wings dipping) and it will cause compression and expansion in the pixels of left and right side of the image

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11
Q

What is the pitch of an airplane? And what does it do to images?

A

The nose or tail of a plane dipping and it causes expansion and contraction in the pixels on the top and bottom of an image

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12
Q

What is the yaw of an image? And how does this effect an image?

A

This is the rotation directionally and it changes the rotation of the pixels

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13
Q

What is image skew in a satellite?

A

As earth rotates as a satellite scans the earth the pixels won’t align properly

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14
Q

What is image to image geometric correction?

A

When you need to compare and image to another the master slave correction will be between two images taken in the same location

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15
Q

What is image to map geometric correction?

A

An image is tied to a map that has the same projection

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16
Q

What is rectification?

A

The linking of a slave image to a master image

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17
Q

What is resampling?

A

The transfer of data from the slave image to the new geometrically corrected images

18
Q

What is geometric correction?

A

Assigning coordinates to an image to make it comparable to another image

19
Q

What is a GCP and what are they used for?

A

Ground control points. They are used to correct the slave image to the master image

20
Q

True or false

GCPs should be clustered in the important part o an image

A

False they should be uniformly distributed

21
Q

What are the two rules of selecting GCPs?

A

Points should be permanent and distinctive

22
Q

What makes correcting images from airborne sensors more difficult?

A

Altitude can be different scan line to scan line

23
Q

What is a frame capture?

A

Aerial photo

24
Q

What formula checks the accuracy of the GCPs?

A

Root mean square error
RMS
This tells how off your points are from eachother

25
Q

When geometrically correcting an image what is the step after selecting GCPs?

A

Generating a new project based on these points

26
Q

What are three ways to generate a new project.

A

Conformal transformation
Affine transform (first order polynomial)
Higher order polynomial transformation

27
Q

What is a conformal transform?

A

A geometric correction used to translate an image in one coordinate system to another. Image must be geometrically correct

28
Q

Why is a conformal transform used? How many GCPs does it use?

A

Scale changes, rotation of images, translation to 3D. 2 GCPs

29
Q

What is a first order transformation/affine transformation?

A

Similar to conformal, but image can only be changed in the x and y directions.

30
Q

How many GCPs are needed for a first order polynomial?

A

3

31
Q

What is a high order polynomial transformation?

A

A geometric correction that does not preserve parallel lines or shape

32
Q

How many GCPs does a high order polynomial require?

A

6 or more

33
Q

What is another term for higher order polynomial?

A

Rubber sheeting. This allows for differing geometry

34
Q

What is the downside of higher order polynomial?

A

Edges of the image become unstable.

35
Q

What are the three types of image resampling?

A

Nearest neighbour
Bilinear interpolation
Cubic convolution

36
Q

What does the nearest neighbour resampling method do?

A

It preserves the true values of the original data. It is referred to as a zero order interpolator

37
Q

Describe a bilinear interpolation resampling method

A

It is referred to as a first order interpolator. This method changes the original values by averaging pixel values

38
Q

What is the advantage of using bilinear over NN?

A

There is a degree of smoothing to the image

39
Q

What is the disadvantage of bilinear?

A

The original data numbers are not preserved

40
Q

Describe how cubic convolution works.

A

It is an improvement on the bilinear in that more pixels are averaged to create new values

41
Q

How is cubic better than bilinear?

A

There is less blur to the image

42
Q

When is it better to use an NN resampling method?

A

When you will be taking measurements from the data

Geography 228 (10 decks)

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