Section 5

Question 1

What are the two types of geometric correction?

Answer 1

Image to image

Image to map/vectors

Question 2

What is an internal geometric error?

Answer 2

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

Question 3

What is another term for internal geometric error?

Answer 3

Systematic distortions.

Question 4

What are the six types of systematic distortions?

Answer 4

Scan skew
Mirror scan velocity
Panoramic distortion
Platform velocity
Earth rotation
Perspective

Question 5

What are external geometric errors?

Answer 5

Movements by the aircraft like altitude change

Question 6

Name and define the two types of external geometric errors

Answer 6

Altitude changes, attitude changes (roll pitch yaw)

Question 7

What does changing altitude effect?

Answer 7

The scale of an image

Question 8

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

Answer 8

Airplanes

Question 9

What is a way to prevent attitude distortions?

Answer 9

Gyro-stabilization equipment

Question 10

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

Answer 10

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

Question 11

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

Answer 11

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

Question 12

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

Answer 12

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

Question 13

What is image skew in a satellite?

Answer 13

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

Question 14

What is image to image geometric correction?

Answer 14

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

Question 15

What is image to map geometric correction?

Answer 15

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

Question 16

What is rectification?

Answer 16

The linking of a slave image to a master image

Question 17

What is resampling?

Answer 17

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

Question 18

What is geometric correction?

Answer 18

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

Question 19

What is a GCP and what are they used for?

Answer 19

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

Question 20

True or false

GCPs should be clustered in the important part o an image

Answer 20

False they should be uniformly distributed

Question 21

What are the two rules of selecting GCPs?

Answer 21

Points should be permanent and distinctive

Question 22

What makes correcting images from airborne sensors more difficult?

Answer 22

Altitude can be different scan line to scan line

Question 23

What is a frame capture?

Answer 23

Aerial photo

Question 24

What formula checks the accuracy of the GCPs?

Answer 24

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

Question 25

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

Answer 25

Generating a new project based on these points

Question 26

What are three ways to generate a new project.

Answer 26

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

Question 27

What is a conformal transform?

Answer 27

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

Question 28

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

Answer 28

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

Question 29

What is a first order transformation/affine transformation?

Answer 29

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

Question 30

How many GCPs are needed for a first order polynomial?

Answer 30

3

Question 31

What is a high order polynomial transformation?

Answer 31

A geometric correction that does not preserve parallel lines or shape

Question 32

How many GCPs does a high order polynomial require?

Answer 32

6 or more

Question 33

What is another term for higher order polynomial?

Answer 33

Rubber sheeting. This allows for differing geometry

Question 34

What is the downside of higher order polynomial?

Answer 34

Edges of the image become unstable.

Question 35

What are the three types of image resampling?

Answer 35

Nearest neighbour Bilinear interpolation Cubic convolution

Question 36

What does the nearest neighbour resampling method do?

Answer 36

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

Question 37

Describe a bilinear interpolation resampling method

Answer 37

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

Question 38

What is the advantage of using bilinear over NN?

Answer 38

There is a degree of smoothing to the image

Question 39

What is the disadvantage of bilinear?

Answer 39

The original data numbers are not preserved

Question 40

Describe how cubic convolution works.

Answer 40

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

Question 41

How is cubic better than bilinear?

Answer 41

There is less blur to the image

Question 42

When is it better to use an NN resampling method?

Answer 42

When you will be taking measurements from the data