Inserting Georeferenced Raster Images

Autodesk MAP includes the ability to properly insert a georeferenced image into a drawing.  A georeferenced image is one that has been scaled, rotated and (when necessary) “rubber-sheeted” into position to correlate to projected map features at a given scale. It may be an aerial photograph, a satellite image or even a scan of an as-built drawing. What makes it distinct from other raster images is the inclusion of correlation data, either directly in the file header, or as a separate “world” file, which provides vital information about the exact location of the image.

The MAP > Image > Insert command is included in stand alone MAP, and also in the version of MAP that comes with Land Desktop. If you have either of these applications, you should completely forget about the AutoCAD image insertion command, and use the one in the MAP menu instead. It does everything the AutoCAD command does, but also offers the ability to detect and take advantage of georeferencing information, ensuring that the image will be inserted exactly where it needs to be.

Naturally, this depends on having a map that is accurately drawn in and assigned to a known coordinate system, another useful feature in Autodesk MAP (see other Map tutorials).  Therefore, it is always important to know what coordinate system a drawing is in, and to identify it properly using the MAP Assign Global Coordinate System command.

So, whether you are inserting a scanned logo into a title block, or a rectified aerial photograph, if you have Autodesk MAP, you should always use the MAP > Image > Insert command. That way, whenever you do have georeferencing information, MAP will use it to display the image the way it was intended.

MAP includes useful tools for adjusting the brightness and contrast of raster images, too, which are useful if you are tiling several images together, if they happen to be exposed differently. It also allows you to “fade” the images, so they can provide useful background information without overwhelming intricate linework and small text.

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