Cartography

Supplement 1

Photogrammetry
• The technique of mesuring objects from photogrammes.
• The first remote sensing technology ever developed, in which geometric properties about objects are determined from
photographic images.
• The process of preparing accurate maps or obtaining precise measurements from photographs

Results of photogrammetry
• Coordinates of the required object-points
• Topographic and thematic maps
• Rectified photographs

Classification of Photogrammetry
Depending on the lense-setting:
• Far range photogrammetry (with camera distance setting to indefinite), and
• Close range photogrammetry (with camera distance settings to finite values).
Another grouping can be
• Aerial photogrammetry (which is mostly far range photogrammetry)
 Topographic maps
 Thematic Maps
 Digital Terrain Models
• Terrestrial Photogrammetry (mostly close range photogrammetry).
 Supervise buildings, document their current state, deformations and damages
 Plastic surgery
 Documentation of traffic accidents and crime scenes

Brief History of Photogrammetry

1851: Only a decade after the invention of the „Daguerrotypie“ by Daguerre and Niepce, the french officer Aime Laussedat develops the
first photogrammetrical devices and methods. He is seen as the initiator of photogrammetry.
1858: The German architect A. Meydenbauer develops photogrammetrical techniques for the documentation of buildings and installs the
first photogrammetric institute in 1885 (Royal Prussian Photogrammetric Institute).
1866: The Viennese physicist Ernst Mach publishes the idea to use the stereoscope to estimate volumetric measures.
1885: The ancient ruins of Persepolis were the first archaeological object recorded photogrammetrically.
1889: The first German manual of photogrammetry was published by C. Koppe.
1896: Eduard Gaston and Daniel Deville present the first stereoscopical instrument for vectorized mapping.
1897/98: Theodor Scheimpflug invents the double projection.
1901: Pulfrich creates the first „Stereokomparator“ and revolutionates the mapping from stereopairs.
1903: Theodor Scheimpflug invents the „Perspektograph“, an instrument for optical rectification.
1910: The ISP (International Society for Photogrammetry), now ISPRS, was founded by E. Dolezal in Austria.
1911: The Austrian Th. Scheimpflug finds a way to create rectified photographs. He is considered as the initiator of aerial
photogrammetry, since he was the first succeeding to apply the photogrammetrical principles to aerial photographs.
1913: The first congress of the ISP was held in Vienna.
until 1945: development and improvment of measuring (=„metric“) cameras and analogue plotters.
1964: First architectural tests with the new stereometric camera-system, which had been invented by Carl Zeiss, Oberkochen and Hans
Foramitti, Vienna.
1964: Charte de Venise.
1968: First international Symposium for photogrammetrical applications to historical monuments was held in Paris - Saint Mandé.
1970: Constitution of CIPA (Comité International de la Photogrammétrie Architecturale) as one of the international specialized
committees of ICOMOS (International Council on Monuments and Sites) in cooperation with ISPRS. The two main activists were Maurice
Carbonnell, France, and Hans Foramitti, Austria.
1970ies: The analytical plotters, which were first used by U. Helava in 1957, revolutionate photogrammetry. They allow to apply more
complex methods: aerotriangulation, bundle-adjustment, the use of amateur cameras etc.
1980ies: Due to improvements in computer hardware and software, digital photogrammetry is gaining more and more importance.
1996: 83 years after its first conference, the ISPRS comes back to Vienna, the town, where it was founded.

Daguerrotype
• an early type of photograph, developed by Louis Daguerre, in which the image is exposed directly onto a mirror-polished surface
of silver bearing a coating of silver halide particles deposited by iodine vapor

Stereocomparator
• A stereoscope that has adjustable scales to allow the determination of distances and dimensions from stereoscopic photographs.

Perspectograph
• An instrument for optical rectification
• An instrument for obtaining, and transferring to a picture, the points and outlines of objects, so as to represent them in their
proper geometrical relations as viewed from one point

ISP
• International Society for Photogrammetry

ISPRS
• International Society for Photogrammetry and Remote Sensing
Photo Devices
• Metric Cameras
o They have stable and precisely known internal geometries and very low lens distortions. Therefore, they are very
expensive devices. The principal distance is constant, which means, that the lens cannot be sharpened when taking
photographs. As a result, metric cameras are only usable within a limited range of distances towards the object. The
image coordinate system is defined by (mostly) four fiducial marks, which are mounted on the frame of the camera.
Terrestrial cameras can be combined with tripods and theodolites. Aerial metric cameras are built into aeroplanes
mostly looking straight downwards. Today, all of them have an image format of 23 by 23 centimeters
• Stereometric Cameras
o If an object is photographed from two different positions, the line between the two projection centers is called „base“. If
both photographs have viewing directions, which are parallel to each other and in a right angle to the base (the so
called „normal case“), then they have similar properties as the two images of our retinas. Therefore, the overlapping
area of these two photographs (which are called a „stereopair“) can be seen in 3D, simulating man´s stereoscopic vision.
In practice, a stereopair can be produced with a single camera from two positions or using a stereometric camera.
A stereometric camera in principle consists of two metric cameras mounted at both ends of a bar, which has a precisely
measured length (mostly 40 or 120 cm). This bar is functioning as the base. Both cameras have the same geometric
properties. Since they are adjusted to the normal case, stereopairs are created easily
• Amateur Cameras
o The photogrammetrist speaks of an „amateur camera“, when the internal geometry is not stable and unknown, as is the
case with any „normal“ commercially available camera. However, also these can be very expensive and technically
highly developed professional photographic devices. Photographing a test field with many control points and at a
repeatably fixed distance setting (for example at infiniy), a „calibration“ of the camera can be calculated. In this case,
the four corners of the camera frame function as fiducials. However, the precision will never reach that of metric
cameras. Therefore, they can only be used for purposes, where no high accuracy is demanded. But in many practical
cases such photography is better than nothing, and very useful in cases of emergency
Photo Techniques
• Mapping from a Single Photo
o Paper Strip Method
 This is the cheapest method, since only a ruler, a piece of paper with a straight edge and a pencil are required.
It was used during the last century. Four points must be identified in the picture and in a map.From one point,
lines have to be drawn to the others (on the image and the map) and to the required object point (on the
image). Then the paper strip is placed on the image and the intersections with the lines are marked. The strip
is then placed on the map and adjusted such that the marks coincide again with the lines. After that, a line can
be drawn on the map to the mark of the required object point. The whole process is repeated from another
point, giving the object-point on the map as intersection of the two object-lines.
o Optical Rectification
 Is done using photographic enlargeners. These should fulfill the so called „Scheimpflug condition“ and the
„vanishing-point condition“. Again, at least four control points are required, not three on one line. The control
points are plotted at a certain scale. The control point plot is rotated and displaced until two points match the
corresponding object points from the projected image. After that, the table has to be tilted by two rotations,
until the projected negative fits to all control points. Then an exposure is made and developed.
o Numerical Rectification
 Again, the object has to be plane and four control points are required. At the numerical rectification, the image
coordinates of the desired object-points are transformed into the desired coordinate system (which is again
2D). The result is the coordinates of the projected points. Differential rectification If the object is uneven, it has
to be divided into smaller parts, which are plane. Each part can then be rectified with one of the techniques
shown above. Of course, also even objects may be rectified piecewise, differentially. A prerequisite for
differential rectification is the availability of a digital object model, i.e. a dense raster of points on the object
with known distances from a reference plane; in aerial photogrammetry it is called a DTM (Digital Terrain
Model).
o Monoplotting
 This technique is similar to the numerical rectification, except that the coordinates are here transformed into a
3D coordinate system. First, the orientation elements, that are the coordinates of the projection center and the
three angles defining the view of the photograph, are calculated by spatial resection. Then, using the
calibration data of the camera, any ray, that came from the archaeological feature through the lense onto the
photograph can be reconstructed and intersected with the digital terrain model.
o Digital Rectification
 The digital rectification is a rather new technique. It is somehow similar to „monoplotting“. But here, the
scanned image is transformed pixel by pixel into the 3D real-world coordinate system. The result is an
orthophoto, a rectified photograph, that has a unique scale.
• Stereophotogrammetry
o As the term already implies, stereopairs are the basic requirement, here. These can be produced using stereometric
cameras. If only a single camera is available, two photographs can be made from different positions, trying to match
the conditions of the „normal case“. Vertical aerial photographs come mostly close to the „normal case“. They are made
using special metric cameras, that are built into an aeroplane looking straight downwards. While taking the photographs,
the aeroplane flies over a certain area in a meandric way, so that the whole area is covered by overlapping photographs.
The overlapping part of each stereopair can be viewed in 3D and consequently mapped in 3D using one of following
techniques:
o Analog
 The analogue method was mainly used until the 70ies of our century. Simply explained, the method tries to
convert the recording procedure. Two projectors, which have the same geometric properties as the used
camera (these can be set during the so called „inner orientation“), project the negatives of the stereopair.
Their positions then have to be exactly rotated into the same relationship towards each other as at the moment
of exposure (=„relative orientation“). After this step, the projected bundle of light rays from both photographs
intersect with each other forming a (three dimensional optical) „model“. At last, the scale of this model has to
be related to its true dimensions and the rotations and shifts in relation to the mapping (world) coordinate
system are to be determined. Therefore, at least three control points, which are not on one straight line, are
required (=„absolute orientation“).
 
The optical model is viewed by means of a stereoscope. The intersection of rays can then be measured point by
point using a measuring mark. This consists of two marks, one on each photograph. When viewing the model,
the two marks fuse into a 3D one, which can be moved and raised until the desired point of the 3D object is
met. The movements of the mark are mechanically transmitted to a drawing device. In that way, maps are
created.
o Analytical
 The first analytical plotters were introduced in 1957. From the 1970ies on, they became commonly available on
the market. The idea is still the same as with analogue instruments. But here, a computer manages the
relationship between image- and real-world coordinates. The restitution of the stereopair is done within three
steps:
After restoration of the "inner orientation", where the computer may now also correct for the distortion of the
film, both pictures are relatively oriented. After this step, the pictures will be looked at in 3D. Then, the
absolute orientation is performed, where the 3D model is transferred to the real- world coordinate system.
Therefore, at least three control points are required.
After the orientation, any detail can be measured out of the stereomodel in 3D. Like in the analogue
instrument, the model and a corresponding measuring mark are seen in 3D. The movements of the mark are
under your control. The main difference to the former analogue plotting process is that the plotter doesn´t plot
any more directly onto the map but onto the monitors screen or into the database of the computer.
The analytical plotter uses the computer to calculate the real-world coordinates, which can be stored as an
ASCII file or transferred on-line into CAD-programs. In that way, 3D drawings are created, which can be stored
digitally, combined with other data and plotted later at any scale.
o Digital
 Digital techniques have become widely available during the last decade. Here, the images are not on film but
digitally stored on tape or disc. Each picture element (pixel) has its known position and measured intensity
value, only one for black/white, several such values for colour or multispectral images.
• Mapping from Several Photographs
o This kind of restitution, which can be done in 3D, has only become possible by analytical and digital photogrammetry.
Since the required hard- and software is steadily getting cheaper, it´s application fields grow from day to day.
Here, mostly more than two photographs are used. 3D objects are photographed from several positions. These are
located around the object, where any object-point should be visible on at least two, better three photographs. The
photographs can be taken with different cameras (even „amateur“ cameras) and at different times (if the object does
not move).

Advantages and Disadvantages of Photographic Mapping

Advantages Disadvantages

Speed in compiling the map. It is not economical for mapping areas of small extent

Reduction in the extent of horizontal and vertical control Difficulty of plotting areas containing heavy ground
survey. cover, such as underbrush, forested areas, and dense
vegetation
High accuracy attained in locating planimetric and
topographic features and details. Difficulty of locating contour lines in flat terrain.

Reduced likelihood of omitting relevant data due to the Necessity for conducting field editing and field
tremendous amount of detail obtained from completion surveys.
photographs.
Initial investment to procure expensive
Significant reduction in cost of undertaking the mapping photogrammetric equipments and their subsequent
operation. maintenance.

Difficulties encountered in surveying rugged and The need to employ skilled personnel to handle
inaccessible terrain are eliminated. sophisticated photogrammetric equipment.

Freedom from interference by adverse weather

conditions during the compilation of the map.

Areas of Photogrammetry

1. METRIC PHOTOGRAMMETRY – this refers to the measurement made on aerial photographs to obtain quantitative data of the
earth’s surface

2. INTERPRETATIVE PHOTOGRAMMETRY – this area is more on recognizing and identifying objects on the photograph, as well as
judging their significance.
Classification of Photographs

1. TERRESTRIAL PHOTOGRAPHS – taken with ground based cameras from known positions or stations with the camera axis
horizontal or nearly so.

2. AERIAL PHOTOGRAPHS – taken by a precision camera mounted in an airplane, balloon, or spacecraft flying over an area.
a. VERTICAL PHOTOGRAPH – the optical axis at the time of the exposure is pointing vertically downwards or perpendicular
to the earth’s mean surface.
b. OBLIQUE PHOTOGRAPH – the camera lens axis points at an angle to the ground. If the horizon is included the
photograph is defined as a high oblique; if not, it is a low oblique.
3. EXTRATERRESTRIAL PHOTOGRAPHS – a type of photograph which has emerged as a result of space exploration. The camera
may be fixed o earth, taken from an spacecraft, contained in a artificial satellite, or positioned on the moon or near planets.

4. COMPOSITE PHOTOGRAPHS – made by joining several photographs taken at a single camera station usually by a multi-lens
camera.
a. DUAL STRIP PHOOGRAPHS (Twinned)– Two cameras are mounted on each side of the aircraft with the axis at right
angles to the direction of flight.
b. TRIPLE STRIP PHOTOGRAPHS – Three cameras are employed during photography, one in the center which points
vertically downward and the other two are tilted as in dual photography.

DUAL STRIP (Twinned) TRIPLE STRIP (Tripled)

c. TRIMETROGON PHOTOGRAPHS – The system has photographic units which consists of three wide angle cameras. One in
vertical position and two in oblique positions and all three cameras are exposed simultaneously from the same aircraft.

COMPONENT PARTS OF AERIAL CAMERA

1. CAMERA BODY – consists of a one-piece casting which houses the drive mechanism for the shutter assembly and the magazine
2. MAGAZINE – consists of a light-tight container which holds the supply of exposed and unexposed film.
3. LENS CONE ASSEMBLY – contains the lens, filter, diaphragm, nodal points, and the shutter.
4. SHUTTER – controls the length of time that light is permitted to pass through the lens.
5. DIAPHRAGM – control the amount of light striking the emulsion of the film which is positioned in the focal plane.
6. FILTER – consists of colored glass placed in front of the camera lens to prevent stray and undesirable light from entering the
camera.