Definition of longitudinal and transverse slabs.

Determining the scale of aerial photographs.

To determine the scale, we use a block layout and a topographic plan of the area depicted in the images. Using a long ruler, we measure two bases: one on the block layout – l , the second – on the plan – L. The measurements are recorded in Table 1. To indicate the basis, we select two points on the plan and on the images, located in opposite parts of the plan (montage). These points on the plan and installation must correspond to the same object. As such objects, the borders of forests, roads, settlements in pronounced places are usually chosen; they must be distinguishable both on the plan and in photographs.

After that, we determine the scale by the formula:

m=L*M/l ,

where M is the denominator of the scale of the topographic plan.

For control and more accurate determination of the scale, another basis (diagonally opposite to the first) is chosen, connecting other points in opposite parts of the image.

As the final scale value, we take the average of the two definitions, rounded to three significant figures.

Table 1 . Logbook for determining the scale of aerial photographs.

basis number Base length (mm) Aerial image scale denominator
Block installation l Map L

m cp = 13888.5

Determination of the photographic quality of aerial photography materials.

Photographic quality depends on the state of the atmosphere, lighting of the subject, technical conditions for aerial photography, photochemical processing. During visual assessment, aerial photographic negatives should not reveal mechanical damage, images of clouds, shadows from them, glare, halos. The image in the pictures should be sharp, with good detail in the light and dark areas. Optical density (tone) and contrast must comply with the regulations. With a visual method, reference images can be used for comparison, i.e. photographs whose photographic quality has been assessed by highly qualified experts. The use of instruments makes it possible to more accurately and objectively evaluate the photographic quality of aerial photographs.

After a visual inspection of our images, we write down the score for each route in Table 2.

Determination of the photogrammetric quality of aerial photography materials.

The photogrammetric quality of aerial photography materials is evaluated according to the following criteria:

Definition of longitudinal and transverse slabs.

For the study, we were provided with materials obtained as a result of a multi-route (areal) photography. It represents the acquisition of terrain images from several parallel routes. Such a survey is carried out with overlapping adjacent images. Overlays are called parts of images that depict the same area. The overlap values are expressed as a percentage of the side length of the shots.

Mutual overlap of images of one strip is a longitudinal overlap, calculated by the formula:

p x =( l x *100%)/ l ,

where l x is the size of the overlapping parts of the image; l is the length of the image side in the direction of the route.

The longitudinal overlap of images is calculated or set based on the technology of photogrammetric processing of images. Its value can be 60, 70, 80, 90%. The overlap of two adjacent shots is called a double overlap, and the overlap area of three shots is called a triple overlap. For each standard value of longitudinal overlap, minimum and maximum limits are determined.

The transverse overlap p y is the overlap of images of neighboring strips. The transverse overlap is calculated by the formula

p y =( l y *100%)/ l ,

where l y is the size of the overlapping part of images of two adjacent strips.

Let’s determine the longitudinal and transverse overlappings by block layout. The amount of overlap is determined using a special ruler that allows you to measure overlap as a percentage. Having made a ruler and measured the overlaps, we write down their values in table 2.

If the aerial photography is performed with a longitudinal overlap of 60% or 80%, then the minimum overlap value is allowed, respectively, 56% and 78%. A minimum transverse overlap of 20% is allowed.

Aerial photography, the materials of which were provided to us, was carried out with a longitudinal overlap of 60%, respectively, the minimum overlap is 56%, but it is not observed for the first route between images 141-138 (see Table 2). Transverse overlap between routes within tolerance.

2. The non-straightness of the aerial photography route begins with the determination of the main points of the extreme images of the route. The main points are the intersection of lines connecting opposite fiducial marks. Then they are connected by a straight line and the distance L between them is measured (Fig. 2).

After that, the deviation l from this straight principal point of the most distant image is measured. This evasion is called the route deflection arrow. The ratio of the deflection arrow to the length of the route, expressed as a percentage, is the non-straightness of the route:

n=l*100%/L

3. The image turn relative to the “herringbone” route direction ε can be determined in two ways: the first one is by measuring the angle ε between the xx line connecting the image fiducial marks and the photographing basis (Fig. 3); the second one is measuring the angle between the route axis and the transverse side of the image. Permissible angles * herringbone * at focal lengths of 100, 140, 200, 350 and 500 mm, respectively, are 5, 7, 10, 12 and 14 ° .

4. The tilt angles of images can be determined by the image of a circular level in one of the corners of the image. If there are no images of levels on the images, then the angles of inclination are determined by the photogrammetric method. During planned shooting, the angles of inclination should not exceed 3 ° .

There are no circular level images in our images, and determination of the tilt angle by the photogrammetric method is not yet within our power. Therefore, we leave dashes in the corresponding column in Table 2.

Table 2 . Journal of Quality Evaluation of Aerial Photography Materials.

route number Aerial date No. of final aerial photographs in the route Number of aerial photographs in the route Photogrammetric quality
Photographic image quality Overlap (%) herringbone degrees Straightness Tilt angle
longitudinal transverse
09/22/83 141-133 Satisfactory 40-79 30-27-25 2.1 0.7
09/22/83 204-196 Chorus. 56-65 45-48-50 1.5 0.2
09/22/83 269-261 Satisfactory 60-65 0.2

As a result of this work, we learned how to make a block layout, determine the scale of aerial photographs, evaluate the photographic and photogrammetric (determine longitudinal and transverse overlaps, herringbone, straightness) quality of aerial photographs.

After evaluating the data of aerial photographs, we see that the photographic quality of the images is good, while the photogrammetric quality corresponds to the standards and is suitable for further photogrammetric processing.

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