Turbocharge Custom Map Creation For Garmin GPS Units

Late in 2009, Garmin added the capability to view raster imagery (like scanned paper maps, and aerial/satellite photography) in their Colorado/Oregon/Dakota/Montana/GPSMap 62/GPSMap 78/Rino 600/Astro 300/Edge 800/eTrex 20 & 30 series of handheld GPS units, using either KMZ image overlays calibrated in Google Earth or with a subscription to their BirdsEye Satellite Imagery service. You can see a full matrix of CustomMaps / BirdsEye compatible units on this page. But the process of putting raster imagery on a compatible GPS unit has significant limitations. For BirdsEye Imagery, these limitations include:

  • A $30/year subscription fee for some Birdseye Imagery datasets (e.g. you need separate subscriptions for US aerial imagery and topographic map).
  • For other Birdseye Imagery types (e.g. UK OS maps), you don’t get unlimited downloads, but have to pay a separate fee based on area.
  • Imagery can be used on only one GPS receiver per subscription; you can’t share it with multiple GPS units.
  • Your choices of available Birdseye imagery are limited to what Garmin currently offers.

Limitations on custom maps created using Garmin’s recommended procedure:

  • Image sizes can be no larger than 1024 x 1024 pixels without automatic and significant reduction in image quality.
  • If you have a larger image, you have to either crop it (reducing coverage), shrink it (reducing quality), or manually chop it up into pieces/tiles and calibrate each tile individually (reducing your free time).
  • You have to calibrate the image in Google Earth, even if your image already has calibration data, like a GeoTiff/MRSID/BSB/IMG graphic file, or an image with a worldfile.

The G-Raster program turbocharges the process of creating raster Custom Maps for your Garmin GPS receiver. It lets you easily convert KMZ overlay files calibrated in Google Earth, using images larger than 1024 x 1024 pixels, by chopping them up into smaller tiles fully compatible with Garmin units; this completely preserves the image’s original quality. It also converts georeferenced map imagery, much of it freely available online, into the KMZ format used by compatible Garmin GPS units without the need for separate calibration in Google Earth. And unlike Birdseye Imagery, KMZ overlay files are always free, aren’t locked to a single unit, and never expire. See this post on the Free Geography Tools website for more information.

Click here to download the G-Raster installer for a free time-unlimited demo version.

Requirements: Windows XP/Vista/7/8; 1 GB RAM or greater.
Minor limitations of free demo version are described below; registering the program for $5 removes all limitations.


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Actual Screenshots Of G-Raster-Created Overlays In A Garmin Oregon GPS Unit

G-Raster Features

=> Scan a map or download a digital map image, use Google Earth to easily calibrate it as a KMZ image overlay, then process the KMZ overlay in G-Raster for high-quality viewing in Garmin GPS units. Accepts KMZ image overlay files created in Google Earth, and chops the entire image into subtiles that conform to Garmin’s 1024 x 1024 pixel size limitation. Supports all graphic image formats accepted by Google Earth for overlays: TIFF, GIF, JPG, BMP, PNG, TGA, PPM, PGM. The unregistered version allows KMZ overlay images up to 1500 x 1500 pixels (2.25 megapixels) in size, and crops larger images down to that size, allowing you to test the functionality. The registered version removes all size limitations, allowing the maximum possible 100 megapixel KMZ overlay image size to be converted and tiled into Garmin-compatible KMZ format.

=> Convert pre-calibrated georeferenced imagery into Custom-Maps-compatible KMZ format, automatically calibrating the image, tiling it, and converting it into the correct format. The largest image size supported for this function is 100 megapixels (10,000 by 10,000 pixels) for both unregistered and registered versions, the maximum allowed by Garmin for most units (Montana owners: please see the help file for special information). There are hundreds of sources of high-quality free data of this kind available online, including:

Supported formats for georeferenced data include GeoTiff; MRSID; BSB NOAA charts; JPG/TIF/MRSID/BMP/GIF/PNG graphic images with worldfile. Experimental support for OziExplorer .map files with accompanying JPG/GIF/BMP/TIF/PNG graphic file. New in version 4.0: Experimental support for ECW files.

=> If you have a standard USGS 1:24,000 topographic map in standard DRG format, like those available at the LibreMap website, G-Raster can automatically crop or “de-collar” the outside border, leaving you with just the map.

=> New in version 4.0: Convert GeoPDF format files to a GeoTiff format fully compatible with G-Raster, and other GPS/GIS programs. These include the next generation USGS 1:24,000 topographic maps, available for free from the USGS Map Store website. Converted USGS topographic GeoPDFs can be “de-collared” automatically in G-Raster to remove the outside border. Please test the tool to make sure it works for you before registering the program, as some GeoPDF files can be problematical. See the help file for limitations on GeoPDF conversion. Demo version limits the size of converted GeoPDFs; registered version removes this limitation.

=> New in version 4.0 (registered version only): Option to export original data files into GeoTiff format used by many GPS/GIS programs; this includes MRSID, ECW, BSB NOAA charts, OziExplorer maps, and graphic images with worldfiles.

=> Map cropping tool (registered version only) lets you select and crop a sub-area of a larger georeferenced map image; useful for removing map collars/borders, and unwanted areas.

=> New in version 5.0: Chop/Crop/Shrink Tool can shrink or crop an image to the 100 megapixel limit automatically, or chops a larger image into smaller 100 megapixel subimages for use with the Garmin Montana series.

=> New in version 4.5 (registered version only): “Border-free” mode creates overlays without the black or white borders created by coordinate system reprojection; see the help file for full details.

=> Metadata tool lets you extract coordinate calibration data from a GeoTiff, and embed it back into a comparable Tiff file. Lets you edit/enhance a GeoTiff file in graphics editors that don’t preserve the metadata, and then re-embed the metadata when you’re done to re-generate a GeoTiff file.

=> For georeferenced imagery, your choice of Mercator projection (default), best at preserving image quality for small areas, or Google Earth’s native cylindrical projection (Plate Carree), best for map imagery that covers large areas. Google Earth KMZ overlays and de-collared topographic maps stay in Plate Carree projection.

=> Lets you adjust the image’s JPG quality factor with a slider, and view the effects of changing this factor with a real-time live preview. A lower quality factor will reduce overall file size, and may improve performance, with little noticeable effect on the image quality.

=> You can rescale the image to a smaller dimension, to reduce the number of tiles and improve performance at lower zoom levels; user-selectable rescaling factor and algorithm. The “Auto Rescale” function automatically computes a rescale factor for optimal tile reduction while still preserving most of the original image’s resolution.

=> Full info on original image size, tile size, total number of size, and highest zoom level you can view the image at without visible pixelization.

=> Custom Map image overlays can be freely distributed, used on any number of compatible Garmin GPS units, and never expire.

=> Custom Map overlays and Birdseye Imagery for the same area can be loaded into the unit at the same time, and turned on and off independently of each other.

=> New in version 5.7: Big KMZ Creator tool. Converts a georeferenced image into an untiled KMZ file, for use with the free Android app Custom Maps. Demo version limits size; registered version removes this limit.

=> Comprehensive program instructions and other useful information available in the program’s help file.

=> Regular updates to add new features, and fix bugs; registered users get access to email help.

Limitations Of Free Demo Version

You can download the installer for a time-unlimited demo version at this link. The demo allows most of the basic functionality, unlimited for personal/non-profit use; commercial users are required to register the program for regular use. Unregistered copies have a nag screen upon program startup; registration for $5, available from the program menu, will:

  • Remove the nag screen permanently
  • Unlock “border-free” mode.
  • Removes size limit on GeoPDF conversion
  • Removes size limit on “Big KMZ” export.
  • Unlock the “export to GeoTiff” option
  • Unlock access to the map cropping tool
  • Give you access to the support email address
  • Support future improvements to the program

You don’t have to download a separate “full” version; registering removes all restrictions in the “demo” version. For now, the program only works in user accounts that have admin privileges (true for most Windows installations) – this is required to run several utility subprograms. If you get a message stating that the “Program may not have installed correctly” (common in Windows 7/8″), go ahead and select the option to reinstall with the recommended settings. And if you have problems getting it to work correctly on your system once installed, try right-clicking on the program icon and choosing “Run as Administrator” from the drop-down menu, or see the help file for instructions on granting admin privileges to the program.

Note: There is a limit of 100 image tiles for Custom Maps for most Garmin units. This is a Garmin firmware limitation, not one for G-Raster. For USGS topographic maps with a small degree of rescaling (1.3 or 1.53 rescale factor), this means that you can fit about 6-8 topographic maps onto your unit. If you need more maps than that, you might take a look at Moagu’s built-in BMap2MP utility; while the map quality can be a bit poorer, there’s no limitation other than memory space on how many topographic maps you can put on your unit. See this page for more info. This limitation has been raised for Montana units; see the program’s help file for more info on this. You can use the program’s Chop/Crop/Shrink tool to prepare large images to meet these limitations.

Having problems registering the program through the eSellerate purchase wizard? Try turning off your firewall temporarily.



Latest version is 6.2, released 7/22/2103; if you have an earlier version, you can update at any time with the installer program. Use the Help => About menu selection to determine your current program version; see the help file for the program history.