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Aerial Photography

The Office routinely performs aerial photography for numerous applications within ODOT.
 
 

 


Equipment

The large format aerial mapping camera is typically used to collect aerial photographs for mapping purposes where high resolution is routinely needed. Our handheld medium format digital camera is utilized to obtain oblique photographs and special assignmensts.

 

Perspective

We typically perform photography from one of two perspectives - vertical or oblique. The vertical photography is normally used for mapping, creating orthophotos and other applications where it is desired to have the scale remain relatively uniform. Oblique photography is usually used when you want to show the magnitude of the subject with an emphasis on details in the foreground.

Example of Vertical Photo

Example of Oblique Photo

 

 

Product Type

 

Aerial photography can be provided in three different product types: black & white, color and color infrared. Black & white imagery was historically used for mapping purposes due to ease of use and reduced cost. Color imagery is currently collected as a standard practice because it can be used for many purposes. Color infrared imagery is typically used for specific purposes such as identification of moisture on the ground and examining the health of vegetation.

 

 

              Ex. Black & White Photo                                         Ex. Color Photo                                    Ex. Color Infrared Photo  

 
Scale

 

The scale of aerial film photography is usually represented in terms of "feet per inch". For example, "250 ft. per inch" means that 1 inch on the film negative is equal to 250 feet on the ground. The image on the film can be enlarged if needed to change the scale.

When using digital cameras, the ground pixel size and dimensions of the sensor array are referenced. For example, one might say they used a 2k x 3k camera with a 4" pixel size. This means that the sensor was 2,000 x 3,000 pixels and the resultant image was composed of pixels each of which represented 4 inches of the ground or subject.

Resolution

 

The term "resolution" can have several technical meanings depending n the use or reference. For example, the resolution of an image using a film media is an indication of the detail of the image in the film itself. The resolution of an image using a digital camera however is the number of pixels per unit of measurement.

The scanning of film media also involves selecting a resolution. Photogrammetric film scanners which are used to scan large format aerial film use increments of microns(0.001mm) for setting the scan resolution.

Resolution is also typically referenced in the printing environment. Some printers or software packages specify dpi(dots per inch), where others note ppi(pixels per inch). Additionally, some printer manufactures use technology such as "continuous tone" implying that you won't be able to see the spacing of the dots which can cause a "grainy" appearance.