Albion 6 CAD User Guide > Drawing > Working With Bitmaps

Bitmaps in Albion are treated like any other object. When you insert a bitmap into a drawing it gets created on the current layer and positioned where you choose. If a bitmap's dimensions are greater than 1024 by 1024 pixels then it gets treated specially, and is managed by the Tiled Bitmap System.

If you are working with aerial photographs, it is advisable to place them on a lower layer and lock the layer once the bitmap is in place. This will prevent you from accidentally selecting the bitmap and moving it around.

How Bitmaps are Located

When a drawing containing bitmaps is saved, the drawing does not embed the bitmaps inside the drawing, but instead stores only the location of the bitmap. Upon loading that drawing again, the system searches for the bitmaps in the following locations, in this order:

1.The location of the drawing file itself.

2.The original exact location of the bitmap.

3.The relative location of the bitmap. This means that so long as you keep your bitmaps in the same directory beneath your drawing, they will always be found.

Aerial Photographs

Aerial photographs typically come in the form of large TIFF, JPEG, MrSid, or ErMapper (.ecw) files. Those are the only 4 formats supported for loading large images. Typically MrSid and ErMapper files have georeference information stored inside them. If not, they are usually accompanied by a small text file with the extension .tfw, .jfw, .sfw, which contains georeferencing information. The Albion bitmap loader automatically detects the presence of such files and uses it to compute the position and scale of the bitmap before insertion. If georeferencing data has been found, it will be made evident in the Bitmap Insert window by the presence of an insertion position that is not (0,0), as well as a scale that is not 1:1. Note that all 4 formats except for ErMapper (.ecw) require preprocessing by the tiling system.

Bitmap Display

The display of a bitmap can be altered by adjusting its contrast, brightness, saturation, and opacity. These properties can be controlled from the standard properties editor.

If the bitmap is accidentally moved inside the drawing

Sometimes one inadvertently moves a georeferenced bitmap that was correctly positioned. This can happen easily if the bitmap's layer is not locked. Should this happen, right-click on the bitmap, and from the pop-up menu choose "Reload Geographical Coordinates". This option will only be available if the bitmap has georeferencing data (either embedded within it or as an accompanying text file). The bitmap will be repositioned.

Changing the geographic coordinates embedded within a BCF file

It may happen that you have a BCF file that has been generated without georeference data, or that the data stored within the file is incorrect. In such a case, the geo data can be modified in the BCF file to reflect the position and scale of a bitmap in a drawing. This is essentially the reverse of "Reload Geographical Coordinates". In order to alter the geodata stored in the BCF file, right-click on the bitmap, and from the pop-up menu choose Update Geographical Coordinates. You will be prompted with a confirmation message.