PHOTOMOD Mosaic — module of orthomosaicking
In a single inseparable process, the PHOTOMOD Mosaic module performs orthotransformation and mosaic creation. All geometric and photometric
distortions are corrected during the orthomosaic creation process. The resultant mosaic can be represented in a given cartographic projection
both as a single image and as a set of sheets of specified size.
Any image from available PHOTOMOD projects can be input for mosaic creation.
Output mosaics can be stored in the following files formats: TIFF, Windows BMP, VectOr RSW,
GeoTIFF, ERDAS Imagine, NITF, JPEG and PNG.
Formats for saving georeferencing data to a separate file: PHOTOMOD Geo, ArcWorld TFW, ArcWorld BPW, MapInfo TAB.
If a mosaic is cut into a number of sheets, raster and georeferencing files are created separately for each sheet.
Types of terrain models used in orthorectification:
- User-defined constant height level
- Ground control and tie points measured in the aerotriangulation step
To increase the quality of the output mosaic, the DTM should include breaklines to describe abrupt forms of relief and vertical objects, such as bridges and houses. Mass
points and breaklines created in PHOTOMOD DTM and StereoDraw modules can be used for this purpose.
- Pixel size
- Output orthomosaic scale. The appropriate resolution is written into the file header as dpi to obtain mosaic hard copy in the specified scale.
- Compression rate for mosaic output. Used to decrease required disk space volume, this setting is only valid for TIFF, GeoTIFF, JPEG formats.
- Background color can be used for areas of the output rectangle image not covered by mosaic. Black is recommended for viewing a mosaic on
screen, while white is recommended for printing.
Output raster format
- Output raster format is dependent on the type of georeferencing file
Inter-image, as well as intra-image, photometric balancing is applied to produce seamless mosaics. Inter-image balancing applies the appropriate
corrections to entire images, while intra-image balancing targets corrections within an image. Seam feathering is applied to the narrow zone
between adjacent images to assure the absence of visible difference across the cutline. Photometric adjustment is automatically implemented
and only requires manual mosaic option adjustments in very rare cases.
The resultant mosaic is created as a single raster image or as a set of sheets. When a mosaic is split into sheets, the sheets can bear the
same parameters (size, number, overlap) or individual parameters. When dealing with sheets of individual parameter, the shape is a user-defined
closed polygon that may differ from rectangular.
By default, the central part of source images with adjusted margin size is identified as a “region of interest” (ROI) to be orthorectified
and included in the output mosaic. ROIs can be edited by drawing cutlines and the order of their placement defined for inclusion into the
Because regions of interest are defined in the source raster image, they can be created before the terrain model is available.
ROIs can be converted from PHOTOMOD vector polygons, as well as imported from number of vector formats.
ROIs can be exported to ASCII, MIF/MID, and DXF vector formats.
For visualization and export purposes, ROIs can be transformed into a set of non-crossing cutlines that define the source image used
to obtain a given part of the output mosaic. This capability further facilitates visual control of the mosaic quality.
The current status of the mosaic project can be saved at any stage of mosaic creation, allowing work to continue from the same point
after reloading the project.
Aerotriangulation points (control, check and tie points) are used to control the geometric quality of the mosaic. The geodetic coordinates
of these points are calculated from their position in the mosaic image and then compared to their values as known from the adjustment results.
A set of residuals are used to calculate statistical parameters. All mosaic accuracy estimation data can be saved to a special report file.
To provide further quality control, vector objects can be overlaid on the orthomosaic. Special tools are provided to measure distances in the
The PHOTOMOD DustCorrect utility removes artifacts like dust particles and photo emulsion defects by replacing them with a small image of similar
texture taken from the mosaic image itself or inserted from Windows clipboard.