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GeoTIFF

Import

Open GeoTIFF or bigTIFF files by loading them directly into the application. The following file extensions are recognized automatically: *.tif*, *.itif*, *.gtif*, *.drg, *.dng, *.btf, *.fx3 .

TIFF files that are not geospatial may also be loaded and georeferenced using the rectification tool.

GeoTIFF data will default to positioning using the information in the TIFF header. See Raster Formats Configuration for additional options. If projection information is found in the header, the application will look for a supported projection file format of the same name in the same directory, and use that (such as .tfw or .prj).

Export

The Export GeoTIFF command allows the user to export any loaded raster, vector, and elevation data sets to a GeoTIFF format file.

• Tiling
• Export Bounds

Export TIFF files from the File> Export menu by choosing Export Elevation Grid Format... or Export Raster/ Image Format.... and specifying GeoTIFF as the Export Format. Individual layers can also be exported from the Control Center by right-click on the layer and going to Layer > EXPORT. Multiple files can be batch converted to and from the format from the Batch Convert/Reproject tool.

When selected, the command displays the GeoTIFF Export Options dialog (pictured below) which displays export options. The dialog consists of a GeoTIFF Options tab, a Tiling tab, and an Export Bounds tab which allows the user to set up the portion of the loaded vector data they wish to export.

File Type

The File Type section allows you to choose what type of GeoTIFF file to generate. The various file types are described below:

• 8-bit Palette Image - This option generates a 256-color raster GeoTIFF file with 8-bits per pixel. The Palette options described below will apply in this case. This option will generate a relatively small output file, at the expense of some color fidelity depending on the palette that you choose. The image data will be compressed using the PackBits compression algorithm.
  

• 24-bit RGB - This option generates a raster GeoTIFF file with 24-bits per pixel. Uncompressed GeoTIFF images generated with this option will be at least 3 times the size of those generated with the 8-bit Palette option, but the colors in the image will exactly match what you see on the screen. You can also maintain the exact colors while achieving some compression using the LZW compression option. Selecting the JPEG compression option generates a raster GeoTIFF file with 24-bits per pixel, but with the raster data compressed using the JPG compression algorithm. GeoTIFF images generated with this option will maintain good color fidelity and often be highly compressed, although they will lose some information as compared to the uncompressed 24-bit RGB option. If selecting this, option keep in mind that many software packages do not yet support GeoTIFF files that use the JPEG-in-TIFF compression option. By default the JPG compression used in the GeoTIFF file uses a quality setting of 75, which can be modified on the displayed options dialog.
  

• Multi-band - This option generates a raster GeoTIFF file with 1 or more bands of data at either 8-, 16-, or 32-bits per band of data. This option is very useful when working with multi-spectral imagery with more than 3 bands of data, such as RGBI, Landsat imagery, or data sets with more than 8 bits per color channel. After selecting this option additional dialogs will be presented allowing for further setup of the multi-band export by choosing the input sources for each band in the output image.
  

• Black and White- This option generates a two color GeoTIFF file with 1 bit per pixel. This will generate the smallest image of these options. However if the source image had more than two colors the resulting image will be very poor. By default, white will be a value of 0 and black will be a value of 1. This can be reversed by selecting the Grayscale - Min Is Black palette option.
  

• Elevation (16-bit integer samples) - This option generates an elevation GeoTIFF using the currently loaded elevation grid data sets. Elevation samples will be stored as signed 16-bit integers. Keep in mind there are only a handful of software packages that correctly recognize a vertical GeoTIFF.

• Elevation (32-bit integer samples) - This option generates an elevation GeoTIFF using the currently loaded elevation grid data sets. Elevation samples will be stored as signed 32-bit integers. Check that vertical units are appropriate prior to using this option, intended for use with high resolution, sub-metric elevation data and values.

• Elevation (32-bit floating point samples) - This option generates an elevation GeoTIFF using the currently loaded elevation grid data sets. Elevation samples will be stored as 32-bit floating point values. Keep in mind there are only a handful of software packages that can correctly recognize a vertical GeoTIFF.

  Note: 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.
  

Palette

When generating a 256 color (8-bits per pixel) GeoTIFF, it is necessary to select a palette indicates what 256 colors will be used to describe the image being exported.

The following choices of palette are available:

Image Optimized Palette

The palette generated will be an optimal mix of up to 256 colors that will closely represent the full blend of colors in the source images. This option will generate the best results, but can more than double the export time required if any high color images are present in the export set. If all of the input data is palette-based and the combined palette of those files has 256 colors or less, then the combined files of the input file will just be used with no additional export time being required.

Grayscale Palette

This palette consists of 256 scales of gray ranging from black to white.

DRG Optimized Palette

This palette is optimized for the exporting USGS DRG data. The palette consists of only the standard DRG colors.

DRG/DOQ Optimized Palette

As the name suggests, this palette is optimized for exporting a mixture of USGS DRG data and grayscale satellite photos (i.e. USGS DOQs). The palette consists of the 14 standard DRG colors with the remaining 242 colors being a range of gray values ranging from black to white.

Halftone Palette

The palette consists of a blend of 256 colors evenly covering the color spectrum. This palette is the best choice when exporting anything but DRGs and grayscale satellite photos.

Spectrum

The spectrum palette consists of 256 saturated colors ranging from magenta to red. The palette goes through various shades with full 255 values for Red, Green, and then Blue successively, varying the other shades.

NLCD (National Land Cover Database)

Palette for the USGS National Land Cover Database. For more information see https://www.mrlc.gov/

CORINE (European Landcover Database

Palette from the Pan-European CORINE Landcover database . For more information see https://land.copernicus.eu/pan-european/corine-land-cover

Global Land Cover ESA

GlobeLand30 (Global Land Cover Database

This palette comes from the GlobeLand30 land cover database. For more information see http://www.globallandcover.com/

ESA/CCI (Climate Change Initiative) Land Cover

European Space Agency Climate Change Initiative Land Cover. For more information see www.esa-landcover-cci.org

Custom Palette from File

This option allows the user to choose a .pal file describing the palette to use for the export. A .pal file should be a text file with one line per color, with the red, green, and blue color components for each color in the palette separated by a comma. A .pal file for an existing palette-based file can be saved by opening the Overlay Control Center, selecting the palette-based layer, Options, Transparent Color button, then selecting the option to save a color palette file.

Grayscale - Min is Black Palette

This palette creates an 8-bit per pixel grayscale image with no color map stored in the image. Black will be stored as zero with varying shades of gray up to white with a value of 255.

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.

Resampling

• Nearest Neighbor - simply uses the value of the sample/pixel that a sample location is in. When resampling an image this can result in a stair-step effect, but will maintain exactly the original color values of the source image.
• Bilinear Interpolation - determines the value of a new pixel based on a weighted average of the 4 pixels in the nearest 2 x 2 neighborhood of the pixel in the original image. The averaging has an anti-aliasing effect and therefore produces relatively smooth edges with less stair-step effect.
• Bicubic Interpolation - a more sophisticated method that produces smoother edges than bilinear interpolation. Here, a new pixel is a bicubic function using 16 pixels in the nearest 4 x 4 neighborhood of the pixel in the original image. This is the method most commonly used by image editing software, printer drivers and many digital cameras for resampling images.
• Box Average (3x3, 4x4, 5x5, and 7x7) - the box average methods simply find the average values of the nearest 9 (for 3x3), 16 (for 4x4), 25 (for 5x5), or 49 (for 7x7) pixels and use that as the value of the sample location. These methods are very good for resampling data at lower resolutions. The lower the resolution of your export is as compared to the original, the larger "box" size you should use.
• Filter/Noise/Median (2x2, 3x3, 4x4, 5x5, 6x6 and 7x7) -  the Filter/Noise/Median methods simply find the median values of the nearest 4 (for 2x2), 9 (for 3x3), 16 (for 4x4), 25 (for 5x5), 36 (for 6x6) or 49 (for 7x7) pixels and use that as the value of the sample location. This resampling function is useful for noisy rasters, so outlier pixels do not contribute to the kernel value. Some common sources of raster noise are previous compression artifacts or irregularities of a scanned map/image.
• Box Maximum (3x3, 4x4, and 5x5) - the box maximum methods simply find the maximum value of the nearest 9 (for 3x3), 16 (for 4x4), 25 (for 5x5), or 49 (for 7x7) pixels and use that as the value of the sample location. These methods are very good for resampling elevation data at lower resolutions so that the new terrain surface has the maximum elevation value rather than the average (good for terrain avoidance). This method behaves the same as the average on raster/imagery layers. The lower the resolution of the export file is as compared to the original, the larger "box" size that should be used.

Sample Spacing / Scale

The Sample Spacing section allows the user to select the grid spacing to use when generating the file. 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.

Selecting Always Generate Square Pixels ensures that the resultant image file will look good even in software that is not able to deal with pixels that aren't square.

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.

Specify the X and Y spacing of the output pixels in any of the selected units. These pixel dimensions will be translated into the units of the display projection during export. The Use Current Screen Pixel Size button will update the X and Y values to the dimensions of the map display. Use Last Exported Sample Spacing will update the X and Y values to the most recent export resolution.

TIFF Format Options

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.

Compression

The Compression selection allows you to select what type of compression to use for the selected export file type. The compression setting will default to the last used value, or LZW Compression. The available compression types are as follows:

• No Compression - The exported data is not compressed. See Raster Formats Configuration to set this as the default.
  

• 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.

Make Background (Void) Pixels Transparent:

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.

ADVANCED: Use Tile Rather than Strip Orientation:

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 this can be customized by creating a DWORD registry key value 'HKEY_CURRENT_USER\Software\Global Mapper\GeoTIFFExport_TileSize' with the desired tile size (such as 256 for 256x256 tiles).

Other Options

Save Scale/Elevation Legend/Grid if Displayed

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.  

Save Vector Data if Displayed

Any loaded vector data that is configured to show up in the main display will be saved to the GeoTIFF file (except vertical GeoTIFFs).

Generate TFW File

A TIFF world file will be generated with the same name as the GeoTIFF file with a .tfw extension. The TFW file is used by software that is not capable of reading the placement of the GeoTIFF file directly from the GeoTIFF header.

Interpolate to Fill Small Gaps in Data:

Any small areas with missing data will be filled in by interpolating the surrounding valid data. This is useful for filling small gaps between adjacent tiles or small holes in elevation data.

Generate PRJ File

A PRJ file describing the projection of the coordinates in the file will automatically be created .

Generate OziExplorer .map File

A .map file describes the location and projection of the data, similar to a PRJ or TWF file. This file is used by OziExplorer and can be read by other applications as well.

ADVANCED: Don't Write GeoTIFF Header

No GeoTIFF tags will be written to the generated file. This is useful for using things like datum specializations that can't be exactly stored in GeoTIFF files, when a PRJ file is preferred

BigTIFF

If the exported file format will be larger than 2 GB, an additional warning dialog will appear.

The normal TIFF format can not handle more than 2GB of data, and typically this will cause truncation of data. The BigTIFF format is a recognized modification to the tiff standard, that can handle up to 4GB of data, but may not be supported by all applications. The recommendation would be to press NO to export as BigTIFF, or cancel the operation and export again specifying a tiling scheme or higher compression setting.

Format Updates

Below is a summary of recent changes to Geotiff export: