Recently, Garmin added the capability to view raster imagery (like scanned paper maps, and aerial/satellite photography) in their Colorado/Oregon/Dakota lines of handheld GPS units, using KMZ image overlays calibrated in Google Earth. But the process has significant limitations:
- 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, shrink it, or manually chop it up into tiles and calibrate each tile individually.
- 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. See this post on the Free Geography Tools website for more information.
Download the G-Raster installer for a time-unlimited demo version here.
  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 (up to 2.25 megapixels in image size for the unregistered version, 100 megapixel image size in the registered version), 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.
- Convert pre-calibrated georeferenced imagery into Garmin-compatible KMZ format, automatically calibrating the image, tiling it, and converting it into the correct format. The maximum size image 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:
- The USGS Seamless Server Site for USGS topo maps, aerial imagery, satellite imagery, and landcover data, among many others
- The NOAA Raster Navigation site for nautical charts
- Many state government websites
- The US Department Of Agriculture for updated Forest Service topo maps and other data
- The free application USAPhotoMaps, which lets you save topo maps and aerial imagery, and also create GPS waypoint files
- And many more
- 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 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.
- Full info on original image size, tile size, total number of size, and highest zoom level you can view the image at without pixelization.
- Full program instructions and other useful information available in the program’s help file.
You can download the installer for an time-unlimited demo version at this link. Some Windows installations will scramble the program layout, where some controls overlap others; if you see this problem, download and run this “fixer” program after the main installer to fix the problem. The demo contains 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.
- Give you access to the support email address.
- Support future improvements to the program.
Screenshot:
Latest version is 2.6, released 2/4/2010; if you have an earlier version, you can update at any time with the installer program. Some people have reported issues with a scrambled program layout, where some controls overlap others; this appears to be Windows-installation-dependent, mainly showing up in Windows XP. If you have this problem, download and run this “fixer” program after the main installation program to fix it. Use the Help => About menu selection to determine your current program version; see the help file for the program history.