Open Printable/Searchable Copy - Global Mapper

Global Mapper User's Manual
• Grayscale - Min is White Palette - This palette creates an 8-bit per pixel grayscale image with no
color map stored in the image. White will be stored as zero with varying shades of gray up to black
with a value of 255.
The Vertical Units field allows the user to select the vertical units to use when exporting elevation data (i.e.
meters or feet). Any input data not in the selected vertical units will be automatically converted on export.
The Resolution section allows the user to selected the grid spacing to use when generating the GeoTIFF. The
default value is the average of the grid spacings of all the currently loaded raster and elevation overlays. If the
Always Generate Square Pixels option is checked, the smaller of the specified x and y resolutions will be used
for both the x and y resolution. Forcing square pixels ensures that the resultant GeoTIFF file will look good
even in software that is not able to deal with pixels that aren't square. If you'd like to specify the spacing in
units other than those of the currently selected view/export projection, press the Click Here to Calculate
Spacing in Other Units button.
If you want to generate a GeoTIFF file corresponding to a particular scale relative to the selected DPI value
(see below), you can check the Export at the Fixed Scale option and then specify the scale to use. For
example, if you specify a scale value of 25000, each inch in the output (an inch being the number of pixels
equal to the specified DPI value) will be approximately equivalent to 25,000 inches on the ground.
The DPI Value to Save in Image option allows you to specify a DPI (dots per inch) value to save in the TIFF
header. Some software, in particular graphics editing software, makes use of this value when sizing TIFF files
for printout. Specifying the default value of 0 will result in the DPI tag not being saved to the TIFF file at all.
The Compression selection allows you to select what type of compression to use for the selected export file
type. The available compression types are as follows:
• No Compression - The exported data is not compressed.
• Packbits - The palette-based image will be compressed using the lossless Packbits algorithm.
• LZW Compression - The data will be compressed using the lossless LZW algorithm. Note that not all
applications can load a LZW-compressed GeoTIFF file.
• CCITT/Fax4 - The 1-bit black-and-white image will be compressed using the lossless CCITT/Fax4
algorithm.
• JPEG Compression - The 24-bit color image will be compressed using the lossy JPEG algorithm.
Note that not all applications support loading JPEG-in-TIFF encoded files.
If the Make Background (Void) Pixels Transparent option is checked for 8-bit palette, 24-bit RGB, or
JPEG-in-TIFF files, an alpha channel will be added to the created GeoTIFF file to indicate which pixels
should be treated as transparent. Note that this will create a larger file and not all applications will support
TIFF files with alpha channels.
If the ADVANCED: Use Tile Rather than Strip Orientation option is checked, the GeoTIFF file will use a
tile-based organization rather than a strip/scanline-based orientation. A tile-based orientation has advantages
when zoomed in on a layer for display, but can be slower when zoomed further out. By default a tile size of
128x128 will be used, but you can customize this by creating a DWORD registry key value
'HKEY_CURRENT_USER\Software\Global Mapper\GeoTIFFExport_TileSize' with the desired tile size (like
256 for example for 256x256 tiles).
If the Save Scale/Elevation Legend/Grid if Displayed option is checked, the distance scale, elevation legend,
and coordinate grid will be saved to the GeoTIFF file (except vertical GeoTIFFs) if they are configured to
show up in the main display.
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