Lecture 2 Flashcards
Earths orbital revolution
an _____ path around the sun
____(angle) with the _____ plane
- An elliptical path around Sun
- Earth–Sun distance varies between aphelion &
perihelion points - 23.50 with the ecliptic plane
Celestial Coordinate system
North & South celestial pole - point in sky directly
above north/south pole on earth (zenith of north/south
pole & + 90o/- 90o respectively)
• Celestial equator – circle surrounding equator on
earth
• Ecliptic – pathfollowed by the sun through the sky over the course of the year.
declination
Declination – angle from celestial equator (0o
), positive going
UP, negative going Down
celestial Prime meridian
• Celestial Prime meridian – point where sun is located at the vernal equinox (spring)
Right ascension
Right ascension (RA)
– angle (degree) from celestial “prime meridian”
(equivalent of celestial longitude) 68
RA – typically expressed as a time going east – 0 to
24 hours is 3600
georeferencing
“To establish a relationship between page
coordinates on a planar map and known realworld
coordinates”.
Or other way
…..is the act of assigning geographic locations
to features of the spatial data that do not have
any real world coordinates
Geographic transformation
Transformation involves: _____, _____, ______, and ______ a dataset to a given set of
geographic or projected coordinates
“The process of converting a digitized map, satellite
image, or aerial photograph from one coordinate system
to another by using a set of control points and a
transformation equation”.
Transformation involves: scaling, rotation,
translation, and skew a dataset to a given set of
geographic or projected coordinates
3 steps in geographic tranformation
Step 1 updates the control points to real-world coordinates. Step 2 uses the control points to run a transformation. Step 3 creates the output by applying the transformation equations to the input features. h
Transformation methods are distinguished by the _______ properties it can preserve and the changes it allows
the changes could be
change of ____ and ____
change of _____
change in _____ and ______
Many mathematical models (equations)
Each method distinguished by the geometric
properties it can preserve and the changes it allows
The changes could be
Change of position and direction
Change of scale
Changes in shape and size
4 Commonly used tranformation methods
- Equiarea Transformation allows rotation and
preserves shape and size - Similarity Transformation allows rotation and
preserves shape but not size - Affine Transformation allows angular distortion
but preserves parallelism - Projective transformation allows both angular
and length distortion. So a rectangle to be
transformed into an irregular quadrilateral
EAT SAUSAGES AT PRISON
______ transformation method is most
commonly use
Affine transformation method is most
commonly use
Resampling of pixel values
Result of geometric transformation of a image is a
new image based on a given coordinate system
New image has no pixel values. These must be
filled through resampling
Resampling refers to filling of each pixel of new
image with a value derived from original image
Various methods exist
3 common resampling of pixel methods
Three common resampling methods:
1. Nearest neighbor resampling:
fills each pixel of the new image with the nearest
pixel value from the original image.
2. Bilinear interpolation method:
uses the average of the four nearest pixel values
from three linear interpolations.
3. Cubic convolution method:
uses the average of the 16 nearest pixel values
from five cubic polynomial interpolations.
NEVER BITE COCKS
Affine Transformation
X = Ax + By + C ……….. (1) Y = Dx + Ey + F ………...(2)
.x, y are input coordinates and X, Y are output
coordinates
.Coefficient C represents translation in the x
direction, and coefficient F the translation in
the y direction
.Coefficients A, B, D, and E are related to
rotation, skew, and scaling
Allows rotation, translation, skew, differential scaling while preserving line parallelism
Affine transformation Allows rotation, translation, skew,
differential scaling while preserving _____ _____
Allows rotation, translation, skew, differential scaling while preserving line parallelism
Affine Transformation properties
the equations requires at least ____ known points to
estimate its six coefficients. Points also known as ____’s
At least ____ known points are commonly used for
reducing problems with measurement errors and to
allow for a least-squares solution
From the ___ ____ ____ (RMS) error value is the
indicator for the goodness of control points that
derives from the least-square equation
The equations requires at least Three known points to
estimate its six coefficients.
The known points are also knows as tics/ground
control points (GCPs)
At least Four known points are commonly used for
reducing problems with measurement errors and to
allow for a least-squares solution
From the Root Mean Square (RMS) error value is the
indicator for the goodness of control points that
derives from the least-square equation.
Polynomial order in transformations
Describe 3 orders of polynomial
- 1st order polynomial (affine)
requires a minimum of 3 displacement links, but should have more
even though 3 gives RMSE=0!
is a homogeneous transformation: only shifts origin, scales and
rotates
straight lines will be preserved - 2nd order polynomial
requires 6 points (displacement links) minimum
is a differential transformation so it “warps” the raster
straightlines on raster may no longer be straight - 3rd order polynomial
requires 10 points minimum
Polynomials are global transformations which strive to achieve a best fit globally or
overall. Only 1st order with exactly 3 points will exactly match control points.
- ___ order polynomial (affine)
- 1st order polynomial (affine)
Root mean square error
The root mean square (RMS) error is a common measure of
the goodness of control points.
It measures the average deviation between the actual (true)
and estimated (digitized or selected) locations of control
points.
The RMS error is derived from the equation:
T OR F
Low acceptable RMS error does not always ensure the data accuracy
T
_____ ______ method is the most commonly used as
resampling techniques that fills each pixel of the new
image with the nearest pixel value from the original image.
Nearest neighbor method is the most commonly used as
resampling techniques that fills each pixel of the new
image with the nearest pixel value from the original image.
Reprojection
Reprojection:
.using data from different projection systems to bring into one system under same
point registration
Registration: bringing to points together that are on different projections/maps but represent the same location
When a map is scanned, an image is divided into individual pixels which are assigned a value based on ________
When a map is scanned, an image is divided into individual pixels which are assigned a value based on grayscale (gray colour level- 0 is black, higher #’s are lighter)
For artimus error you need _____ control points
4
GIS STORES two types of geographic information : _______ and ______
attribute
features
The functions of a GIS are _______, geodata _______, and geographic ________
visualization, management, analysis,
Geographic Data vs Data
(a collection of) facts about a geographic entity (Earth’s physical features, inhabitants, and phenomena) from which conclusions may be drawn
a collection of facts from which
conclusions may be drawn
Geographic Data model
the methods of representation of
geographical data into the computerized
geographic information system.
• The location of a geographic entity is linked
to a geometry (point, line, poly, or a pixel),
which refers to as spatial data.
• Then the geometry is linked to its attribute(s).
• An attribute could be quantitative or
qualitative.
Geographic data can be ______ or _______ data
spatial(features) and Attribute data
spatial–>Qualitative and Discrete
Attribute data–>Quantitative and Qualitative–>discrete and continuous
What is a node?
What is a polygon?
Nodes: connect multiple lines (start node and end node)
Polygon: all the lines connect together and enclose a shape
Continuous vs Discrete:
- Elevation
- Aspect
- Land Use
- Rainfall
- Vegatation Type
- Pollution
- Roads
- Wells
discrete: Land use, Vegetation type,
Roads, Wells
Continuous: Elevation, Aspect,
Pollutions, Rainfall
Spatial Data is split in two: _____ and ____
raster and vector
Vector Data model
- it uses points and their coordinates to
represent spatial features as points, lines, and
polygons
Dimensionality and property distinguish the
point, line, polygons - it organizes geometric objects and their spatial
relationships into digital data files that
computer can access, interpret, and process
Features are generally represented in Coordinates are most often pairs (x,y) or triplets
(x,y,z, where z represents a value such as elevation).
Describe Point, line , and Polygon
Point
•No length, width or height, only location implied
•Defined by x, y coordinates
•Also called a node or vertex
Line
• defined by a set of connected points
• One-dimension, length, determined by the
distance between the end points
• Lines also known as edges, links
• Examples: roads, streams, contour lines
Polygon
• Two-dimension, length and width give area and
perimeter
• Boundary is defined by a set of lines
• Examples: political entities, water bodies
Raster Data Model
Cell - also known as pixel Cell value , Cell Size Rows, number, Columns, number Number of bands Attribute table in raster dataset
Raster data represent
points by a single cells,
lines by sequences of neighboring cells,
and
areas by collections of contiguous cells.
Some raster datasets contain attribute tables Typically cell values can represent or define a class, group, category, or membership
E.g.: a satellite image may have
undergone a classification
analysis to create a raster
dataset that defines land uses
Cell values can be Integer or Floating-point
In _____ data model what is integer and floating-point?
Integer: Number with no decimal digits Used for represent categorical data or discrete data e.g.: land use, forest category, soil type
Floating point: Number with decimal digits Used to represent continuous data Require more computer storage space e.g.: precipitation, slope, DEM
4 types of attribute data
1.Nominal
• data are qualitative only,
• no computation possible
. no data order
2.Ordinal
• qualitative or quantitative,
• represent an order of the
individuals
3.Interval
• quantitative only
• a zero entry simply represents a
position on a scale
4.Ration
• Interval type with a meaningful zero entry
• a ratio of two data values can be formed so one data value can be expressed as a ratio of the other.
NEVER ORDER INDIAN RICE
Metadata
The term refers to any data used to aid the
identification, description, quality, reference
information, entry information, distribution
information and data authority, etc. of geospatial
data.
Topology
Topology is a mathematical approach of
studying those properties of geometric objects
that remain invariant under certain
transformations such as bending or stretching.
i.e. topology remains constant through
distortion
When a map is stretched or distorted, some
properties of objects are changed:
Distance, Angles , Relative proximities
Some properties won’t change, Adjacencies and incidence Spatial relationships, such as "is contained in", "crosses" Types of spatial objects - areas remain areas, lines remain lines, points remain points These unchanged properties are called topological properties.
Topological Data and GIS
a spatial database is often called “topological”
if the topological relationships have been
computed, stored, and maintained. Such as,
connectedness of links at intersections
ordered set of lines (chains) forming each
polygon boundary
adjacency relationships between areas
Evolution of Vector Data
Model by ESRI systems In “Georelational Data Model” and “Object Oriented data model”
Describe all 4 within these two models
Georelational Data Model: First two
1980’s: PC Arc/Info Workstation Arc/Info began with a coverage data format
1990’s: ArcVIEW then used ‘shapefile’
Object Oriented data model: These two
2000’s:ArcGIS 8 & 9 then started using geodatabase
2010: ArcGIS 10.x continued with geodatabase
Georelational Data Model- coverage
Based on the georelational data model, an Arc/Info
Coverage has two components:
A set of graphic files for spatial data and
A set of INFO files for attribute data.
The label connects the two components through feature ID.
“Coverage” is the name of a GIS data layer in ESRI Arc/Info
data structure.
A “Coverage” in Arc/Info data structure is like a Folder, that
contain a number of files.
Some of the files represent spatial feature geometry,
Some files for attribute data, and
some others for holding other information, such as maximum
spatial extent, annotation, projection parameter, etc.
“Coverage” maintains topological properties in spatial data
structure
collection of multiple ‘coverage’ is called a __________
workspace
what is a tic file?
Tic file= use to pinpoint where info came from
Shapefile
Also known as ESRI ArcView Shapefiles.
Geographic features in a shapefile is also
represented by points, lines, or polygons (areas)
File-based based data
collection of graphic and info files
same file name but different extensions (suffixes)
The workspace may also contain dBASE tables,
which can store additional attributes that can be
joined to a shapefile’s features.
Geodatabase
3 feature geometry types
Geodatabase data model is an Object-based
data model
The Geodatabase model is a collection of
objects, properties and methods held in
a common file system
a Microsoft Access database
or a multiuser relational database
e.g.: Oracle, Microsoft SQL Server, or IBM DB2
Point feature: represented as single point
or multi-point set of points
Polyline feature: a line or a set of line
segments, which may or may not be
connected.
-User-shaped, Curves, Single / multi-part
Polygon feature: a set of one or many rings.
a ring is a set of connected, closed, nonintersecting
line segment.
-Single / multi-part
Polyline vs. line
-polyline feature instead of line because it can be a set of line segments which may or may not be connected
.lines all have to be connected somehow
Geodatasets in Geodatabase
Feature class
Stores spatial data of the same geometry type
Can be broken down into subtypes
Feature dataset
Stores feature data classes that share the same
coordinate system and area extent
Feature classes included in a feature dataset ‘share’
topological relationships with each other
Contains different theme layers, multiple dataset
Standalone feature class Feature class that is not included in a feature dataset
Feature Data set vs. Feature class
Feature dataset
Stores feature data classes that share the same
coordinate system and area extent
Feature classes included in a feature dataset ‘share’
topological relationships with each other
Contains different theme layers, multiple dataset
Feature class
Stores spatial data of the same geometry type
Can be broken down into subtypes
Spatio-temporal vs. Non-spatio-temporal
Spatial (absolute location, shape, size)
Temporal (time, duration, frequency)
Spatio-temporal (changes in a spatial description
over time, example change of extent)
Non-spatial (name, owner, quality, color, …………)
Non-spatio-temporal (changes in a non-spatial
descriptions over time, example change of colors)
General GIS Spatial/temporal info analysis
GIS provides data, tools, and methods that
enable the representation, description,
measurement, comparison, understanding
relationships, and modeling the past and
present of spatial phenomena and prediction
of future.
GIS Data Anlysis
Single-layer analysis
e.g.: how close each other, how different from
each other in pattern landuse classification
Multi-layer analysis
e.g.: change detection pre & post desaster,
spatial model Universal Soil Loss Equation
(USLE)
Integrated analysis
- both spatial and attribut data
- involves attributes, location and topology
Attribute Data Query
Attribute data query retrieves a data subset by
working with attribute data
Selection of attribute data or the data
query requires an ______
expression
ArcGIS uses SQL (Standard Query Language)
for query expressions
SQL (Structured Query Language)
designed for relational databases, by IBM in the 1970s,
and used by many commercial database management
systems
The basic syntax of SQL includes the following:
.select [ selects fields as a list]
.from [name of the table of the database]
.Where [specify the selection criteria]
Query expressions consist of ______ _____ and ______
Query expressions consist of Boolean
expressions and connectors
Boolean expressions: A simple Boolean expression contains two operands(Parcel.Pin and P101) and a logical operator(=) .ex: Parcel. PIN = ‘P101’ -Other operators [ =, , >=, <=, <>]
Connectors:
Boolean connectors are AND, OR, XOR, and
NOT are used in query functions and overlay
operations.
.Connect two or more expressions in a query
statement.
.NOT, AND, and OR are actually used in the
operations of Complement, Intersect, and
Union on sets in probability
Boolean Connector: “Not”
The blue shaded portion represents the complement
of data subset B–>contains elements of the set A that
do NOT belong to B
Boolean Connector: XOR
Everything in subset A and B except what is in both A and B
Boolean Connector: Or
The union of data subsets A and B
the set of elements that belongs to A OR B
Boolean Connector: and
The intersection of A and B
the set of elements that belongs to both A AND B
Spatial Data Query:
Uses a graphic, such as a circle, box, line or
polygon to select features that fall inside or are
intersected by the graphic
Examples:
.selecting restaurants within a radius of a hotel
.selecting land parcels that intersect a proposed
highway, or
.finding owners of land parcels within a proposed
nature reserve
Spatial Data Query: Feature Selection by ______
explain
Uses a GRAPHIC, such as a circle, box, line or
polygon to select features that fall inside or are
intersected by the graphic
Examples:
.selecting restaurants within a radius of a hotel
.selecting land parcels that intersect a proposed
highway, or
.finding owners of land parcels within a proposed
nature reserve
Feature Selection by Spatial Relationship
3 spatial relationships
Select features based on their spatial relationship
to other features
.In the same layer or in different layers
.Containment, intersect, proximity
Containment
.Select features that fall completely within features for
selection,
.E.g.: Schools within a particular county or state
parks within a particular state
Intersect
.Select features that intersect other features
.E.g.: Selecting land parcels that intersect a proposed road, urban areas that intersect a fault line
Proximity
.Select features within a specified distance of other
features
.E.g.: State parks within ten miles of an interstate highway
Vector Data Analysis
Vector data analysis uses the geometric objects
.What are those?
-point, line, and polygon.
.The accuracy of analysis results depends on
-the accuracy of these objects in terms of location and
shape.
Topology is an important factor for some vector
data analysis such as buffering and overlay.
Buffering: Vector Data Analysis
.is based on the concept of proximity
.is a single layer operation
.creates two areas:
1. within a specified distance of selected features —-buffer zone
2. the other area that is beyond the buffer zone
.Buffering around points, lines, and areas:
3 Variations in Buffering for Vector Data Analysis
- distance can vary according to the values of a
given field - buffering around line features can be either on the
left side or on the right side - boundaries of buffer zones may remain intact
so that each buffer zone is a separate polygon
Methods of Overlay In vector Data
Relationship–>containment and overlaps
Multi-layer operation
-layer must be spatially registered
-based on same coordinate system
An important consideration in a overlay operation
is the feature types.
Two groups
1. Uses two polygon feature layers
2. Uses one polygon feature layer and the other point
or polyline-feature layers
polygon-on-polygon
point-in-polygon
line-in-polygon
Overlay
Combines the geometries and attributes of two
feature layers to create a single output layer with a
modified set of attribute table.
Each feature on the output contains a combination
of attributes from the input layers
Vector:
polygon-on-polygon
point-in-polygon
line-in-polygon
For overlay you always use ______ as the overlay theme. Output is the same as input!
Polygon
Input: Point= Output: Point
Boolean Operators: Overlay
AND: True for all areas that meet both criterion
ex: which areas are steep and forested
OR: True for all areas that meet atleast one of the two criterion
ex:which areas are steep or forested
XOR: True for all areas that meet ONLY one of the two criterion. Cannot be BOTH
ex: which areas are either steep or forested
NOT: True for all areas that meet the first criterion but not the second
ex: which areas are forested but not steep
Match name with associated boolean operator
Intersect=____
Union=_____
Symmetrical Difference or Difference= ____
Identity or Minus=_____
- Intersect if it uses the AND connector
- Union if it uses the OR connector
- Symmetrical Difference or
Difference if uses the XOR connector - Identity or Minus
Explain Dissolve(_____ _____)
Identical to spatial merge
Removes boundaries between polygons
or nodes between arcs
Features with same attributes are dissolved
Underlapping
“Under-lapping” features from input layer are erased
Order of input layer and overlay layer is important
clip
“Cookie cutter” Only input theme features and attributes exist in output Polygon on polygon, line, or point
Eliminate
It merges the selected polygons with neighbouring
polygons keeping the largest shared border or the
largest area
“Eliminate” is used most often to remove sliver polygons created in an overlay of two layers
Append
Append combines features from two or more
layers into a single output layer
It does not calculate new topological
relationships between the resulting features.
T OR F
Appending calculates new topological relationships between the resulting features
FALSE
Split
Split creates output layer by overlaying two sets of features. Split performs a series of Clip operations, one for each output layer. Each output layer contains only those portions of input layer features that are overlapped by the specified polygons of the Split Layer.
Raster Data Analysis
Raster data model
-a regular grid to cover space
-value in each cell represents a characteristic
Popular use in application model
Various type of raster data (GRID, DEM, DRG…)
Software package defines what type raster data can
be analyzed–>required conversion
large variety of analysis operations
Map Algebra is used for ____ data analysis
RASTER
Algebraic operations in
a single layer or
multiple raster layers
output is a single layer
Statistics (max, min, range, mean, median, mode, sd..) of the input layers cell values to the output layer
Majority, minority, or unique value of the input layers cellvalues to the output layer
Multi-layer analyses are Similar to the vector overlay
operations
In map algebra explain how to get the MAJORITY and MEAN
Majority: most common number from input layers
Mean: average all inputs
Two types of energy used in remote sensing
Incident energy-from sun
Reflected energy-from ground by up to sattelite
Remote sensing can be done at 4 positions:
Ground observation
Low altitude
High Altitude
Satellite
Camera
Cameras are framing systems which acquire a
near-instantaneous “snapshot” of an area (A), of
the surface.
Camera systems are passive optical sensors
that use a lens (B) (or system of lenses
collectively referred to as the optics) to form an
image at the focal plane (C), the plane at which
an image is sharply defined.
Things to consider for determining what makes
one photograph different from another
-The film
-Focal length
-Scale
-Look direction and angle
optics
system of camera lenses
focal plane
focal plane (C), the plane at which an image is sharply defined.
Stereoscopic analysis
Stereoscopy, sometimes called stereoscopic imaging, is a technique used to enable a three-dimensional effect, adding an illusion of depth to a flat image. Stereopsis, commonly (if imprecisely) known as depth perception, is the visual perception of differential distances among objects in one’s line of sight.
7 Recognition elements for ariel images:
shape, size, pattern, shadow, tone/colour, texture, site/association
SSPSTTS
Photos taken from ______ are the most widely used because:
Photographs taken from aircraft remain the most widely used source of imagery for large-scale mapping. Because: aerial photographs are usually high resolution, have a simple geometry they can easily interpreted with the unaided eye or simple instruments
Describe how camer generally works
All cameras rely on the same essential features:
– Light enters a darkened enclosure (camera, from the
Latin word for room) through a small aperture, the size
of which can often be controlled mechanically
– A shutter is opened and closed to admit light for a
specified period of time
– Inside the camera, a glass lens gathers and
concentrates the light, focusing it on a light sensitive
field at the back of the camera
• Traditionally - the film
• Today, in digital cameras, employ arrays of detectors to record incident energy levels
Camera Film:
• The films are basically coating of light
sensitive emulsion over a base material,
• Most air photo missions are flown using
black & white films, however Infrared,
colour, and colour infrared (CIR) film are
sometimes used for special projects
Panchromatic
• Panchromatic: films are sensitive to light from 0.3 μm to 0.7 μm that covers ultraviolet (UV) and visible (VIS) portion of the EM spectrum, good for infrastructure mapping.
Infrared
• Infrared: Infrared films response to light from 0.3 μm to 0.9 μm,
which covers UV, VIS and Near Infrared (NIR) portion
Infrared films are useful for detecting differences in vegetation
cover, due to its sensitivity to IR reflectance
Water becomes darker in IR Image than that in Panchromatic
image. Exposed soil is brighter in IR image than that in
Panchromatic image
EM RADIATION:
EM radiation is the carrier of electro-magnetic energy by transmitting the oscillation of the electric and magnetic fields through space or matter.
Shorter the wavelength = _____ the frequency
HIGHER
_______ the wavelength = lower the frequency
longer
Human eye has a spectral sensitivity from __um to __um which is termed _______ wavelength of the EM spectrum
The spectral sensitivity of the human eye is
from about 0.4 to 0.7 μm which is termed as
visible wavelength of EM spectrum.
• The main classes of visible wavelength are:
• blue is about 0.4 to 0.5 μm
• green is about 0.5 to 0.6 μm
• red is about 0.6 to 0.7 μm
Main Classes of visible wavelength and um’s
- blue is about 0.4 to 0.5 μm
- green is about 0.5 to 0.6 μm
- red is about 0.6 to 0.7 μm
LIDAR
LIDAR: gives more elevation information than digital
HEAT IS _______ WAVELENGTH AND CAN PASS THROUGH WALLS WHILE LIGHT IS ______ WAVELENGTH AND CANNOT
LONGER
SHORTER
Two important parts of photos from camera
Principal Point
Field of view
. Principal point: most central point of photo
. Field of view: total area captured by camera
Two general types of Black and White film
Panchromatic, Infrared
Colour film
involves the use of a three layer film with each layer
is sensitive to different ranges of light
.Usually the top layer sensitive to Blue light, and
second and the third layers sensitive to the Green
and Red respectively
.However, the second and the third layer also sensitive to the Blue light,
therefore a filter is used in between the first and the second layer to
blocking the penetration of Blue light
.These photos appear to us as the same way that our eyes see the
environment (i.e. trees appear green, etc.)
.Major advantage of colour film is that the human eye can discriminate
many more shades of colour than the tones of grey
Colour infrared film
…was developed during WWII to detect painted
targets that were camouflaged to look like
vegetation and cannot be detected by the color
photography
……also involves a three layer film where keeping
the red and green sensitive layer, the blue light
sensitive layer is replaced by the NIR light sensitive
layer
It produces photograph with non natural color. In the process photograph, taken in color infrared, features showing high intensity of Green appears as blue and Red appears green, and feature that has high reflectance in NIR band that appears as Red
–> vegetation appears as red
Why choose Colour Infrared over natural colour?
excellent haze penetration characteristics than normal color film because the shorter wavelengths are not recorded
good used for mapping forest and agricultural areas and detection of vegetation stress caused by insect damage, disease, flooding, or other factors
Water, which absorbs NIR strongly and appears blue to black, which clearly delineates the waters edge and makes it easier to map.
Even streams partially obscured by vegetation are much more easily distinguished on color infrared film than on normal color imagery
Comparison of Different Films: Advantages of each
- Advantages Panchromatic B&W and Normal color over infrared film:
- Advantages of Infrared over Panchromatic B&W and normal Color :
- Advantage of normal Color over Panchromatic B&W :
- Advantages of Panchromatic B&W over normal Color:
1.Advantages Panchromatic B&W and Normal color over infrared film:
More natural to the eye
Better resolution
Better penetration over water
2.Advantages of Infrared over Panchromatic B&W and normal Color :
Better penetration of haze
Emphasizes water and wet areas
Good differentiation between hard wood and conifers
Good differentiation between healthy and diseased trees
3.Advantage of normal Color over Panchromatic B&W :
Human can discriminate 20,ooo – 5 million shades of color, but only
about 200 shades of grey
- Advantages of Panchromatic B&W over normal Color:
Color film is more expensive to process
Resulting images on color prints are usually not as sharp as on B&W prints
2 main types of photography: angle of photos and description
Vertical :
.Camera optical axis < 3 degrees off vertical
Oblique: 2 types
•Camera optical axis > 3 degrees off vertical
High oblique=horizon visible
Low oblique=horizon not visible
Some advantages of vertical aerial
photography
• Vertical photographs present approximately uniform
scale throughout the photo
• Constant scale allows the determination of directions
(i.e., bearing or azimuth) in the same manner as a map
and easier to interpret
• Minimal mathematical correction required to use
photogrammetrically
• Stereoscopic study is also more effective on vertical
than on oblique photographs
• They may be used as a map if a coordinate system
and legend information are added
Some advantages of oblique aerial
photography
• Oblique photographs covers much more ground area
• Area frequently covered by cloud layer may have
enough clearance for oblique coverage
• Have a more natural view because we are accustomed to seeing objects obliquely with perspective
• Objects that are tall may be visible
• Determination of feature elevations more accurate
• They may be acquired from inexpensive cameras
Photogrammetry
• Photogrammetry is the art and science of
making accurate measurements of objects by
means of aerial photography (Jensen, 2006);
• or is the technique of obtaining reliable
measurements of objects from their
photographic images.
• Some of the important measurements that can be
obtained from a single vertical aerial photograph using
either analog or digital photogrammetric techniques
include:
Scale of the photography
Object height (buildings, tree crowns…)
Object length
Area of an object or polygon
Perimeter of an object or polygon, and
Grayscale tone or color of an object
Stereo Viewing
Successive photo pairs display the overlap region
from different perspectives and can be viewed through a device called a stereoscope to see a three
-dimensional view of the area, called a stereo
model.
Many applications of aerial photography use stereoscopic coverage and stereo viewing.
Finding scale in Aeriel Photography: 2
1.Finding scale from the known features:
• Scale is the ratio of the distance between two points on a photo to the actual distance between the same two points on the ground (i.e. 1 unit on the photo equals “x” units on the ground)
• If a 1 km stretch of highway covers 4 cm on an air photo, the scale is calculated as follows:
-Photo distance/ground distance=scale
2.• Another method uses the ratio between the camera’s focal length and the plane’s altitude above the ground being photographed.
• If a camera’s focal length is 152 mm, and the plane’s altitude Above Ground Level (AGL) is 7 600 m, using the same equation as above, the scale would be:
-Focal length/Height Above Ground= Scale
Scale(RF)=f(focal point)/H(height above ground)=f/A-h
Height above ground= Altitude-h(Terrain Elevation)
REMEMBER TO USE THE SAME UNITS(mm or cm not both)
Scale(RF)=__/__
Height Above ground= _____-_______
Scale(RF)=f(focal point)/H(height above ground)=f/A-h
Height above ground= Altitude-h(Terrain Elevation)
Determining scale:
Example 1: f = 152.4 mm, H = 3,000 m
Example 2: f = 152.4 mm,
A = 12,000 m, h = 2,000 m
Scale = 0.1524 m / 3,000 m
= 1/19,685 => 1/19,700
Scale = 0.1524 m / (12,000 - 2000) m = 1/65,616 => 1/65,600
Relief Displacement
.is the shift in an object’s image position caused by its elevation above a particular datum
Scale is not constant across uncorrected air photos,
.Scale decreases towards the lower elevation areas of the landscape captured on a photograph .
Any point will be displaced outward from the Principal Point relative to any lower point in the area.
Orthorectification to remove the relief
displacement and correction of scale
_______ to remove the relief
displacement and correction of scale
Orthorectification to remove the relief displacement and correction of scale
Relief displacement radiates out from Nadir (PP)
Objects at the Nadir do not have any displacement
______(Principal Point)
Nadir
the point on the celestial sphere directly below an observer.
Length, example a shadow, can be found
The length, L, can be found by taking the length of the
shadow measured on a photo (0.10 inches) and
multiplying it by the photo scale (1:4000). So, 0.10 inches on the photo is 400 inches in the real world, or 33.33 feet.
So, if you know the time and date of the photograph
and figure out what was the sun`s angle, the
height of the object can be measured.
Figuring out Sun Angle:
A 30 meter tall building can cast a 5 meter long shadow. What is the angle of elevation of the sun?
tan (-1)a=h/L
Tan-1a=30/5=6
Tan-1a(6)
=80.53 degrees
PAY ATTENTION TO UNITS
Figuring out Length of the shadow:
• The length, L, can be found by taking the length of the shadow measured on a photo (0.10 inches) and
multiplying it by the photo scale (1:4000). So, 0.10 inches on the photo is 400 inches in the real world, or 33.33 feet.
PAY ATTENTION TO UNITS
Match images through stereoscope using ______/_____ POINTS
-as you move away from points things get distorted
PRINCIPAL/FOCAL
