Vertical aerial photograph is an aerial photograph technique where the shots are taken from directly above the subject of the image. Hence, this method of aerial photograph is also often referred to as “overhead aerial photograph. Oblique photographs (also known as oblique aerial photographs or oblique air photographs) are taken from a high point, which is at an angle neither horizontal (ground level photograph) nor perpendicular (vertical aerial photograph) to the area being photographed.
The following are advantages of vertical aerial photograph over oblique aerial photograph;
- Vertical photographs present approximately uniform scale throughout the photo but not oblique photos. It follows that making measurements (e.g., distances and directions) on vertical photographs is easier and more accurate.
- Because of a constant scale throughout a vertical photograph, the determination of directions (i.e., bearing or azimuth) can be performed in the same manner as a map. This is not true for an oblique photo because of the distortions.
- Because of a constant scale, vertical photographs are easier to interpret than oblique photographs. Furthermore, tall objects (e.g., buildings, trees, hills, etc.) will not mask other objects as much as they would on oblique photos.
- Vertical photographs are simple to use photogrammetrically as a minimum of mathematical correction is required.
- To some extent and under certain conditions (e.g., flat terrain), a vertical aerial photograph may be used as a map if a coordinate grid system and legend information are added.
- Stereoscopic study is also more effective on vertical than on oblique photographs.