G-Raster

Recently, Garmin added the capability to view raster imagery (like scanned paper maps, and aerial/satellite photography) in their Colorado/Oregon/Dakota/62/78 lines of handheld GPS units, using KMZ image overlays calibrated in Google Earth, or with a subscription to their BirdsEye Satellite Imagery service. You can see a full matrix of Custom-Maps-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:

  • Limited to satellite/aerial imagery only; no topographic maps, or any other maps, are available as part of this service.
  • There’s a $30/year subscription fee.
  • Imagery can be used on only one GPS receiver per subscription; you can’t share it with multiple GPS units.
  • Imagery expires unless you renew your subscription.

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 lets you easily convert KMZ overlay files calibrated in Google Earth with images larger than 1024 x 1024 pixels into a tiled format fully compatible with Garmin units, and which 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; 1 GB RAM or greater.
Minor limitations of free demo version are described below; registering the program for $5 removes all limitations.



sf sf

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


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 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 Garmin-compatible KMZ format, automatically calibrating the image, tiling it,  and converting it into the correct format. The largest image size supported is 100 megapixels (10,000 by 10,000 pixels) for both unregistered and registered versions, the maximum allowed by Garmin. There are hundreds of sources of high-quality free data of this kind available online, including:

Supported formats for georeferenced data include GeoTiff, MRSID, ERDAS Imagine, and BSB NOAA charts; also JPG/TIF/BMP/GIF/PNG graphic images with worldfile.

=> If you have a standard USGS 1:24000 topographic map in standard DRG format, like those available at the LibreMap website, G-Raster can crop or “de-collar” the outside border, leaving you with just the map.

=> 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.

=> 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 JPG quality factor with a slider, and view the effects of changing this factor with a 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 “Autoscale” function automatically computes a rescale factor for the highest possible tile reduction while still preserving image resolution.

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

=> 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.

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

Limitations Of Free Demo Version

You can download the installer for a free time-unlimited demo version at this link. The demo allows most of the basic functionality, but with a nag screen; registration for $5, available from the program menu, will:

  • Remove the nag screen permanently.
  • Unlock the limitations on KMZ overlay file image size.
  • Unlock access to the map cropping tool.
  • Give you access to the support email address.
  • Support future improvements to the program.

Note: You don’t have to download a separate “full” version; registering removes all restrictions in the “demo” version.

Having problems registering the program through the eSellerate purchase wizard? Try turning off your firewall temporarily. You can also register the program on a different computer, then contact me for information on how to transfer the registration to your main computer.

Screenshot:

G-Raster-2.0

Latest version is 3.4, released 8/22/2010; 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.