Photograph interpretation

Photograph are the true image pictures showing truly appearance of the earth’s surface objectives on the flat bodies of special pieces of paper taken with the use of a camera and chemically printed. Or

Are the pictorial representations of the remote sensed data recorded on film in a camera then chemically printed on special pieces of paper.

With respect to the definition given, photography is produced as the image of the object captured and recorded with a camera on a light sensitive film. The film by then is developed in a developer machine to remove darkness in it to develop brightness of object’s image. The image in the film by then printed on a special paper using chemicals to develop clear true image pictures. The camera recording the images of objectives can be mounted on the ground or aerial platform.

A person who takes photography with the use of a camera is called photographer; and the art of producing these pictures is known as photography.

Photographers have potential significance in geographical studies in a number of ways. For in stance; they are used to asses the geographical facts of respective areas. Alternatively used to make storage (recording) of the geographical details of pieces. It has to bear in mind that, land details change with time,But a photography once produced remains unchanged. Some of the geographical details that can be assessed from photographs include; relief, land use, drainage features, settlement and vegetation.

TYPES OF PHOTOGRAPH ON GEOGRAPHICAL PHENOMENAL.

Photographs are not all the same as images of objects on them observed to have varied appearance. The varied appearance of image objects are determined by the orientation of the camera axis (Photographic views). Thus; photographs are classified according to the appearance of the images on them relatively to the orientation of the photographic views. Also; photographs are classified by considering the nature of platform from which the camera and photographic view has been mounted and set. By regarding the two categorizing factors, the numerous photographs are broadly classified into the following types. ·

1. Horizontal/ground photographs.

2. Vertical aerial photographs.

3. Oblique photographs.

4. Satellite photographs.

GROUND (HORIZONTAL) PHOTOGRAPHS

These are the photographic prints of which whose images have been captured and recorded on film as photographic views horizontally set with camera mounted on the platform of the ground I e the photographic view by camera towards the object is from the surface level of ground the camera is placed fixed on a tripled stand very close to the ground comparatively Ground photographs are also known as terrestrial photographs.

The horizontal photographic view may target a particular object or the general scenery of the area it is thus; the horizontal photographs may show major object or the general scenery of the area basing on this; horizontal photographs sub divided into two

a) Close up ground photographs

b) General view ground photographs

Close up ground photographs.

These photographs are produced as the photographic view focuses on a major item such as a tree a person an animal a house and others of the same reflection The particular item obscures most of the other details behind it and thus the picture shows a died ground These photographs are alternatively known as particular view photograph

General view ground photographs.

These are taken by the photographic views with mounted camera focusing the general scenery of areas commonly; the photographic view are not intercepted by an obstacle as a result all objects at an area recorded on the film and printed to appear on the photo by getting progressively smaller from the fore ground to back ground hence; the photograph give the general view of the scenery this photograph shows horizons.

Horizon means part of the photograph where the land and sky apparently meet.

Close up ground photograph

General view ground photograph

Characteristics of ground photograph.

1. On the ground photographs particularly objects get progressively smaller from the fore section to back section and horizons likely to be seen.

2. The ground close up photographs do not show horizons.

3. They cover smaller areas of ground.

4. They do not make uniformity coverage of the ground represented.

5. Scale changes by getting progressively smaller from the fore ground to back ground due to the non uniformity coverage of the ground.

6. They show front views of the object’s image.

7. Ground photographs are taken from surface level.

Strengths of the horizontal photographs.

1. The objects on the photograph are clearly seen.

2. It is easy to interpret as the image of objects is clearly observed on the photograph.

3. They are less expensive to be produced compared to other types of photograph.

4. Comparatively; horizontal photographs are the most familiar pictures to people compared to other forms of photographs.

5. Ground photographs can be used as an aid to field sketching.

6. They give more easily instant data of areas.

Setbacks of the horizontal photographs.

1. Cover smaller area size of the ground. It is thus; enables people to make analysis of geographical features of small areas.

2. Subjected to scale distortion as image of objects as well as ground coverage get progressively smaller from the fore ground to back ground this makes difficult to asses the used scale.

3. They are not potential for assessing the measurement of the geographical features like; area size and distance due to scale distortion.

4. Not all objects are seen on the photograph as some are hidden by others

5. They are not potential for map making due to scale distortion and coverage of smaller areas . Note

6. Horizontal photographs are produced purposely to have an aid for making geographical analysis and description of the smaller areas

VERTICAL PHOTOGRAPHS

These are photographic prints whose images of objects have been captured and recorded on film as photographic views vertically set with camera mounted on the platform of the aircraft. i.e. the earth’s surface is viewed vertically from the air craft with the camera axis at almost right angle of 90 though the angle can be displaced to either 87 or 93 due to the movement of the aircraft

According to the history the first vertical aerial photograph was taken from a balloon by a French man in 1855 and were much improved in Germany However; the importance of these photographs for map making became during the first and second world wars when maps were needed for military purposes. Vertical aerial photographs have less scale distortion and mostly used for map making and assessments of the geographical features and measurements.

Characteristics of the vertical aerial photographs.

1. They display the top view of the objects as photographic view vertically directed towards the landscape.

2. The image of objects on photographs appear less distorted in size.

3. They are taken with camera axis vertically directed.

4. They make considerably uniform coverage of ground.

5. They are less subjected to scale distortion.

6. The change of scale by getting progressively smaller is from the centre to outwards

Advantages of the vertical aerial photographs

1. They have less scale distortion following the uniformity coverage of the landscape on the photo

2. It is possible to judge the photo scale as there is uniformity coverage of the landscape on the photo and images are less distorted in size. Scale is assessed by relating the corresponding measurements between the photograph and ground or by relating the focal length of the used camera and flying height of air craft above the ground

3. Cover larger area of the ground. It is thus; people make geographical analysis of the wider geographical areas

4. They are mostly used in map making because of covering wider areas and less scale distortion

5. It is possible to make photogrammetric i. e. They are used to asses measurements of the geographical features as whose scale almost is less distorted

6. Vertical aerial photographs can be viewed stereoscopically. i. e. images can be viewed in three dimensions with the use of a stereoscope

7. They provide instant data particularly those which can not be given by the horizontal photographs e. g. the volume of moving objects at a time such as cars ships etc

8. They can provide details of the impenetrable or remote areas which can not be visited by ground surveyors or photographed horizontally. e. g. swampy land dense tropical forest, desert interiors ice caps and others of the same consideration

Disadvantages of vertical aerial photographs.

1. Objects are not clearly seen as very huge area covered and only the top view of objects are displayed

2. It is some how difficult to make photo interpretation as objects are not clearly seen

3. They show only the top views of the land objects taken

4. The taking of the vertical photographs is affected by the adverse weather E. g. cloud cover during the rainy season

5. The taking of the vertical photographs is still an expensive process

6. Minor detail is often lost in vertical aerial photographs and need to be supplanted by ground survey

7. Because of being non selective; vertical photographs are wasteful as show masses of details some of which may not be needed in the analysis and description

OBLIQUE PHOTOGRAPHS

These are the photographic prints of which images have been captured and recorded on film as photographic views tilted with mounted camera from either aircraft or elevated ground. Tilting of the aircraft can be from low oblique photographs which only show the surface. Tilting of the photo graphic view from high height produces the high oblique photographs which commonly show both horizons and surface. By regarding from where the tilted photographic view set; oblique photographs are divided into two and include;-

a) Ground oblique photographs/low oblique

b) Aerial oblique photographs/ high oblique

Ground oblique photographs

These are the photographic prints whose images have been captured and recorded on film as photographic views tilted with mounted camera from elevated ground e.g. from a hill looking down. These make smaller coverage and are termed as low oblique aerial photographs.

Aerial oblique photographs.

They are the photographic prints of which whose images have been captured and recorded on film as photographic views tilted with mounted camera from aircraft

Characteristics of oblique photographs.

1. Images of objects on the photograph get progressively smaller form the fore ground to back wards.

2. Subjected to scale distortion as there is no uniformity coverage of the ground on the photograph.

3. The change of scale by getting progressively smaller is from the fore section to back section.

4. Show both side and top views of the objects.

5..  Images on the photo are highly displaced as they occupy apparently linear position

Advantages of the oblique photographs

1. Objects on the photograph are relatively large in size. Hence they are clearly seen.

2. It is easy to interpret the photograph as images of objects in them are clearly viewed.

3. They show both side and top parts of the objects.

Disadvantage of oblique photographs.

1. They suffer from the problem of image displacement i.e. the objects on the photo are observed to occupy the linear position.

2. They are subjected to scale distortion as objects get progressively smaller from the fore ground to backwards. Hence it is difficult to judge the used photo scale.

3. They are not used for map making due to scale distortion.

4. They are not potential for assessing the measurements of the geographical features.

Differences between the oblique and vertical photographs.

1. Vertical aerial photographs cover larger area size of the ground, while; oblique aerial photographs cover smaller area size of ground.

2. Vertical photographs show only the top view of the objects; while oblique photographs show both side and top views of objects taken.

3. Oblique aerial photographs show both the surface and horizons while the vertical aerial photographs show only the surface.

4. Oblique aerial photographs show displaced images; while the vertical photographs do not show displace images.

5. Oblique photographs are much subjected to scale distortion; while the vertical aerial photograph is less subjected to scale distortion.

6. The change of scale by getting progressively smaller is from the centre outwards on vertical aerial photographs while on the oblique aerial photographs are from the fore section to back section.

7. Vertical aerial photographs display much smaller images of the objects; the oblique photographs display relatively large sized images of the objects.

8. Vertical aerial photo is used in map making while the oblique aerial photo is not used in map making.

SATELLITE PHOTOGRAPHS

These are the photographic prints whose images recorded (taken) electronically with the use of a scanner as a sensor placed in a satellite.

Or

photographs of earth and other planets made by means of artificial satellites in which multi spectral scanners installed (equipped)

The scanning view is directed towards the land space from the satellite operating in a very high altitude. Satellite operates at vertical distance of 900km above the mean sea level.

The satellites are equipped with sensitive receptors called multi spectral scanners which reflect details from the earth’s surface. The data recorded by multispectral scanners are relayed (sent) electronically to ground stations where with other electronic machines the imaginary data processed to develop photographs which give much details up on meteorological condition, geology, soil, pollution, forests, and crops.

The satellite imagery have daily used for weather for forecasting, provide information for mapping, land use and plotting the landscape details and other uses.

Types of satellite imagery.

Satellite imagery are recognized by considering types of data they display.

Land sat satellite imagery: – these provide details about earth’s resources.

Meteosat satellite imagery: – these provide meteorological data for daily weather forecasting.

Uses of satellite imagery.

1.  They are used to forecast the weather conditions likely to occur in some days to come.

2. They are used to monitor forest fires, ice flows and ocean currents.

3. They are used for resources assessments. i.e. satellite photographs are used to reveal the resources which present in different parts of the earth’s surface.

4. They are used for mapping purposes. The boundaries of countries, continents and other features which appear on maps mostly traced from the satellite imagery.

5. They are used for environmental management.

6. Satellite imagery facilitates scientific studies. For instance; satellite imagery used to detect sea surface temperatures.

7. They are used for military purposes. Satellite imagery provide secure communication for the military.

Disadvantage of satellite imagery.

1. They are most expensive to be produced as it can be compared to all other forms of photographs.

2. They are difficult to be processed.

3. They require high skill to be interpreted because of their colour composites.

IMAGE DISPLACEMENTS, SCALE DISTORTION AND PARTS OF THE PHOTOGRAPHS.

IMAGE DISPLACEMENTS. (PARALLAX)

On some photographs, the images of objects do not appear uprightly vertical as are in real life. They are observed to appear displaced by occupying apparently linear position. This in the study of photographs is knows as image displacement. It is thus; image displacement is defined as the photographic setting of objects on the photo to occupy apparently linear position.

The scientific term used to describe and explain image displacement is known as parallax. Hence; parallax is defined as the apparent shift in position of an object on the photo with respect to reference point. By reference point refers to the position of an object on the photo.

Causes of image displacements.

1. The change of viewing position

If a photograph is taken by the tilted photographic view, the images of objects on the photo are made to have both top and side views and thus;    appear displaced. With respect to this; oblique photographs are the ones which have highest degree of image displacement compared to horizontal and vertical photographs.

2. Height of the viewed objects.

This makes variation in the degree of displacement of objects on a photograph. The higher objects are more displaced that the smaller objects on the photo. For instance; the high buildings on oblique photographs appear more displaced compared to the smaller buildings.

3. Position of the object on the photo.

Usually objects at a nadir (principle point) are less displaced compared to those that are away from the Nadir (principle point) this is observed on vertical photographs, the objects on the fore ground have low degree of displacement compared to those on the back ground. But this factor is mostly considered to objects of the same height.

Note

Image displacement is one among the sources for image displacement on photographs.

SCALE DISTORTION.

On photograph scale is changed by getting progressively smaller from one section to other sections. This in the study of photographs is referred as photo scale distortion. It is thus; photo scale distortion defined as the variation in relation ship (ration) of distance between the photograph and ground by getting progressively smaller from the principle point outwards on vertical photographs or from the fore ground to backwards on horizontal and oblique photographs. However; the degree of photo scale distortion is much higher on oblique and horizontal photographs than on vertical photographs.

CAUSES OF SCALE DISTORTION.

Scale distortion is made by the following causal factors.

1. Non uniformity coverage of the ground.

The section on photograph that covers small area is subjected to large scale, while that covers wider area is subjected to small scale.

2. Distortion in size of the objects.

Objects that appear apparently smaller make small scale compared to those which appear apparently larger.

3. Image displacement.

More displaced objects make small scale compared to objects which are less displaced.

PARTS OF PHOTOGRAPHS.

Photographs are used to make description and analysis of the geographical features observed with reflection to be actual areas represented. The features described should give their position location on the photographs. The location position of the features is by pointing out parts of the photographs where the features are found. It is thus important to understand the major parts of photographs in such a way that the features can be described and analyzed clearly.

Parts of photographs are recognized by dividing the photographs horizontally and vertically into three dimensions

Horizontal division makes a photograph to have three equal parts of; fore ground, middle, ground and back ground.

Middle ground

Vertical divisions makes a photograph to have three equal parts of; left, centre and right.

If both horizontal and vertical divisions combined, a photograph is made to have nine equal parts. The main parts include the following:-

Fore ground:

This develops; left fore ground, centre fore ground, and right fore ground.

Middle ground:-

This develops; left back ground, centre ground and right ground.

Back ground:–

It develops; left back ground , centre back ground and right ground.

Note:

The nine parts of the photographs as already pre described have the following vital significance.

They are used for position location of the features on the photograph in the course of making description.

They are considered for diagrams drawing from the photograph. i.e. they are used to place features on the diagram at right positions.

VERTICAL PHOTOGRAPHS SCALES.

Photograph is much smaller in size, while objects represented are much large in size. It is thus; photographs being much smaller subjected to have considerable relation of distances to the much

large objects represented. This is what referred to photo scale. It is thus; photo scale is defined as the relation ship of distance between the photograph and their respective object represented.

The scale of a photograph is not much up on the decision of the photographer. It is thus; once a photograph produced, its scale should be assessed to allow further assessment of the geographical features. In this aspect; it is possible to asses’s scales for photo graphs which make uniformity coverage of ground. Hence it is difficult to assess specific scale for horizontal and oblique photographs whose specific scales can be assessed.

Photo scale extremely varied in size and the most common types are large and small photo scales depending on the size of the ground covered. Coverage of smaller area make large scale, while coverage of wider area make small scale.

The scale of the vertical photograph relatively to the size of the ground covered is the function of the following determinant factors:-

Focal length of the camera used.

Flying height of the air craft above the ground.

PHOTO SCALE EXPRESSION.

The assessed scale can be expressed in one of the following techniques.

In ration form. 1:50,000

In unit equivalent. e.g. 1cm on the photo = 0.5 km on the ground.

In statement; e.g. 1cm on the photo represents 0.5 km on the ground.

PHOTO SCALE DETERMINATION.

Scales of the vertical aerial photographs are determined by two methods and they include the following:-

By relating the corresponding distances between the photograph and ground. The distances should be measured and the application is as follows:-

Ground distances obtained in the one of the following two ways:-

By making actual measurement at the photographed area.

The use of scaled topographical map representing the same photographed area.

Example:-

Ground distance from area A to B is represented by 5cms on the photo. The same ground distance is represented by 10 cm on a topographical map drawn on the scale of 1:50,000. Determine the photo scale.

Solution.

The photo scale is determined as follow:-

According to the given data:-

Photo distance = 5 cm

Map scale = 1:50,000

CD on the map = 10 cm.

Thus; the photo scale; 1:100,000

By relating the focal length and flying height above the ground. The technique (method) is applied as follows

While:-

F = focal length of the used camera.

Hg = flying height of the air craft above the ground.

Note:-

Flying height of the air craft above the ground does not on the photography. What directly appears on the photograph is the flying height of the air craft

above the sea level. It is thus; the flying height above the ground is obtained by subtracting the ground height from the flying height of air craft above the sea level.

Where by:-

Hg = The height of the aircraft above the ground.

H = Height of the air craft above the sea level.

g = Ground height above the sea level.

Example:-

Determine the scale of the vertical aerial photograph taken with the camera of 6″ if the flying

height are 7,000m and ground height 4,000m respectively.

Solution:-

Scale for vertical aerial photography up on the given data is determined as follows:-

While; Hg = H – g According to the given data:- f = 6′

H = 7,000m

g = 4,000m

6”

7,000m – 4,000m

15 cm

3,00m

15

300000

1

20,000

Thus; the photo scale; 1: 20,000 Note:-

The focal length of the used camera is determined as follow.

The height of the air craft above the ground is determined by the following application.

The height of the aircraft above the sea level is determined as follow.

Where by:-

H = Height of the air craft above the sea level

Hg = Height of the air craft above the ground.

G = Ground height above the sea level.

Exercise.

An air craft flying at the same level over the terrain ground took two photos over the coastal plain that was at the sea level and mountain peak respectively, using the camera of the same focal length. The first photo scale was 1; 37,000 taken at 4500m a.s.l. and the second photo scale was 1:20,000

Calculate the camera focal length.

Determine the altitude of the mountain peak.

Calculate the height of an area shot by a camera whose focal length is 132mm mounted on an air craft which is flying at 10500m above the sea level. The suggested scale is 1:25000.

A vertical photograph with suggested scale of 1:20,000 has been taken by photographic view set

from air craft at altitude of 5000m. The used focal length was 6″ (15cm).

Determine the imperial altitude of the photographed area.

What metric scale the photograph may have if the photographic view set at altitude of 400m.

Calculate the flying height of an aircraft for the vertical aerial photograph at the scale of 1:20,000 whose mean ground level is 500m above the mean sea level with the focal length of

210mm

152mm