photomosaic

what is a mosaic?

An aerial mosaic is an assemblage of two or more individual over lapping photographs to form a single continuous picture of an area . The assembly is made by cutting and piecing to gather part s of photographs , being careful to make common images coincide as closely as possible at the match lines between adjacent photos

First photomosaic

Types of photomosaics

•Uncontrolled mosacis

•Controlled mosaics

•Orthophotomosaics

Uncontrolled mosaic This is the easiest to create, but does not

significantly correct for image displacement in the original airphotos.

The mosaic is produced by aligning them(photographs) with images or features on the airphotos. For less image displacement, the centers of the airphotos can be cut out (since they have less displacement) and aligned.

Uncontrolled mosaics are commonly used for photo indexing.

An uncontrolled photomosaic

Controlled mosaic

 Each airphoto is corrected for aircraft height and tilt variations.

The central portion of the airphotos are cut out and aligned with adjacent airphotos in a similar fashion as use for uncontrolled mosaics. Each photo is then further oriented by matching features with survey control points for the area.

Controlled mosaic

Orthophotomosaic• This process is the most accurate in that it tranforms the airphotos into a larger mosaic that has characteristics of a map (true distance, angles, areas) but can be interpreted like a photograph.

• The process of conversion is called differential rectification and involves the elimination of photo scale variations and image displacement using an instrument called an orthophotoscope.

An orthophotomosaic(Nelson, British Columbia)

Need of photomosaic?

• to create a meta image with larger coverage area.

Mosaic advantages

Show relative planimetric qualities , whereas objects on maps which are shown with symbols must be limited in number .

Mosaic of large areas can be prepared in much less time and at considerably lower cost than maps

it is easy to understand and interpreted by people without photogrammetry or engineering back ground .

Uses of mosaic

Mosaic are widely used . Their value is perhaps most appreciated in the field of planning , both in land-use planning and in planning for engineering project .

Use to study geologic features.

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