Creating GPS Maps from Raster Images;
How to display USGS Topo maps on your Garmin®, using the "Autovectorization"
feature of Mapwel™ Software
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Figure 1: Cashiers Topo Quad
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Figure 2: West Glacier Topo Quad
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Figure 3: Disc Golf Course at Baylor Regional Park
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Figure 4: Everglades National Park, Florida
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Figure 5: Fire Map, Ventura County
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Figure 6: Crime Map, Georgia Tech (Atlanta), GA
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For years, GPS enthusiasts have been wanting a Garmin that will display USGS topo maps, but topo maps are typically found as raster images and Garmins use vector maps - two completely different ways of storing and rendering maps images. Raster maps are like pictures with the smallest details represented by a pixel. Vector maps are points, lines, and polygons stored and displayed using their mathematical constructs. Converting pixels into points lines and polygons, is usually a task for professional cartographers and expensive software tools - until now. Here is are some examples of maps I have made for my Garmin nuvi, using the Autovectorization feature of Mapwel software.
Update 15 May 2008: The autovectorization feature of Mapwel was recently revised with significant improvements in processing speed and color differentiation.
Mapwell Software
First, some history about Mapwel Software ( mapwel.eu ). I first used Mapwel in March 2005 to create a background map for my Garmin from a drawing of a proposed new development. The software has a simple user interface for creating maps in a Garmin compatible format and transferring the maps to the GPS. It is an all-in-one solution that is easier to use than solutions that require separate programs to create maps, covert them to Garmin format, and yet another to transfer to the device. It was easy to create a subdivision map from my drawing and then go to the property and walk the lot lines.
Now, Mapwel has evolved with more features and support for more devices. In addition to the subject of this article, I was very please to learn about support for Garmin car navigation devices and the ability to import ESRI shape (.shp) file format.
Pixels to Polygons
The "Autovectorization" process is a one-click operation after importing and georeferecing your suitable map image. Following the developers guidance for map coverage and coloration, I was able to create several several examples. The USGS topo map of Cashiers, NC ( Figure 1 ) is a fine example, where the mapping purist will immediately recognize the artistic beauty of the United States Geological Survey's unique cartography. I started with the quadrangle in paper form and scanned a 2 kilometer square area at a resolution of 600 dpi.
Note: Mapwel automatically adjusts number of colors and resolution of the image, but if you want to load several autovectorized maps into GPS at the same time, you should reduce number of colors yourself and set the same color palette to all images. This is necessarry in case of multiple maps, because GPS can store only one color palette at once. Current version of Mapwel supports max. 86 colors, which is sufficient to display subtle color shadings, while preserving capability to combine autovectorized map with common maps that use default set of polygons.
Having the map already in PhotoShop, I simply selected "Save for web..." from the File menu, and in this case, I set 8 as the maximum colors to use in .gif format. Then, to georeference the map image in Mapwel, I retrieved the coordinates of image extents using ExpertGPS software. I note that OziExplorer users do not have to georeference the image in Mapwel if they import OziExplorer calibrated image. After georeferecing and by selecting Image>Automatical Vecotrization, the process starts, few seconds or minutes depending on the amount of map detail and size..
Focus on Resolution
Autovectorization process automatically resamples raster image for optimum vectorization. The resampling ratio may vary for different maps. The developer of Mapwel, Dusan Balara, advises that resolution of the source map image is an important to getting good results displayed on the GPS. Balara recommends resolution of the original image to be not worse than 2.4 m per pixel. The best resolution to use is about 1 m per pixel.
I recommend that you keep total coverage to less than 20 x 20 km as these files can get very large. It will take your GPS several seconds to render large maps.
Converting Other Images to Vector Maps
This process produces very good results of maps from aerial images and from thematic maps.
Satellite Images
Here are two examples of vector maps made from aerial photos. Figure 3 is an image from the Carver County, Minnesota web site, showing an annotated, aerial image of the Disc Golf Course at Baylor Regional Park. Even with a limited color palate you can see subtle differences in ground cover. The original image can be seen here: www.co.carver.mn.us
Figure 4 is a GPS map made from a satellite image of the Everglades taken from Google Earth. Here you can clearly see mangroves in green, the dark brackish waterways, white beaches, and brown shallows.
Google Earth provides a wealth of satellite imagery for use in this mapping process, and it is easy to export an image of the desired area for use with the Mapwel program. Within the Google Earth program you simply, send yourself an email with the image attached by selecting File > Email > Email image... (or Cntrl+Shift+E). Then, you follow the standard procedure of opening the image in a photo editing program and save it as .gif or .png file, making it ready for use in Mapwel where you will georeference, autovectorize, and upload to your GPS.
Thematic maps
Thematic maps are typically simple maps, which convey information about a particular subject. Two example included here are land maps maps showing areas burned by fire and street maps showing neighborhoods crime rates, ,
Figure 5 is a GPS map made from a map image of the Zaca fire in Ventura County, California (8/23/2007) which can be found at http://fire.countyofventura.org/documents/zacaupdate.asp.
Figure 6 is a GPS map made from a screenshot of DeLorme Street Altas software with crime zone overlay downloaded from here.
Vectorized Map in Practice
All the results I have shown so far have been nuvi screenshots with the GPS in simulation mode. To see how these maps work in the field, I created a simple map of my neighborhood and went for a drive. I found that map showed my location accurately and the location cursor (little car) followed the road. At first I tired "North Up" map orientation, the switched to "Track Up" orientation. Both orientations worked equally well, but I notice that the little car had to move from its usual place on the screen every time the map had to redraw. It was as if the device was working hard to keep up with displaying the map at the proper location.
Limitations and Recommendation
Mapwel is a great program for getting started making your own Garmin compatible background maps. The Autovectorization feature enables the beginner to create useful maps from readily available resources in just a few clicks. However, your GPS will not draw the Mapwel autovectorized maps as quickly as it draws standard vector maps which have been painstaking created to maximize storage efficiency and map drawing speed. Also, these are not auto-routing maps - for viewing only.
I recommend this method of creating GPS maps from aerial photos covering up to 20 x 20 km, color enhanced to highlight ground features, territories, or to symbolize a particular theme, and for use viewing only at slower than highway speed (i.e. golf course, battlefield, park, etc.)
Contact me to make a GPS map for your orginization,
- Doug
BTW For more information about these procedures, the Mapwel software includes
a short "video" on how to import and georeference images, and
the autovectorization process is outlined at the Mapwel
web site.
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More Info about Mapwel Software
All in One
The creation of a GPS map involves drawing the map, conversion of the map
data into the GPS's native format and uploading of that data into the GPS.
Mapwel allows user to do all 3 tasks in a single program. User does not
have to convert data from one program to another until the map is loaded
in GPS, and to struggle with each program's conventions.
Easy to use
Mapwel has very user-friendly graphic environment that allows user to draw
and edit maps in a vector form. Number of automation tools simplifies creation
of maps: automatical split of areas and lines to conform GPS technical requirements,
automatical handling of holes in areas, etc. All data (scanned bitmap, imported
tracks and waypoints) are stored in a single MPW file to simplify the files
management.
Curves
Unlike other mapping programs, Mapwel provides curves along with polylines
for drawing of vector objects. Curves allow faster drawing of map because
much lower number of curves is needed for approximation of object's
contour than straight lines. Moreover, use of curves anbles user to
control size of data uploaded into the GPS because curves are automatically
sampled into polylines with adjustable number of lines.
Compatibility
Mapwel supports number of map formats, including the widely used ESRI
shapefiles. User can easily import detailed maps and upload them into
GPS within few minutes. ESRI shapefiles support is included even in
the basic version of Mapwel. Mapwel software includes stand-alone freeware
program MAPupload.exe that serves for upload of IMG files (Garmin GPS
native file format) created in other software into the GPS.
Add Map function
When uploading your map into the GPS, other software usually deletes
all other maps in the GPS memory. Mapwel allows to add map to existing
maps. Note: this function does not work when map loaded in GPS uses
unlock code.
"What You See Is What You Get"
Mapwel is designed to facilitate as comfortable work on maps as possible,
User can draw lines and areas in any color and special viewing modes
display how the map will look on monochrome or color GPS display (WYSIWYG
interface) anytime during the drawing process.
Datums conversion
Internal datum of Mapwel is WGS84 because GPS internal format is WGS84
too. Mapwel allows user to convert coordinates from 280 local datums
to WGS84 when drawing map.
Zoom levels
To make map displayed on a GPS small display legible, Mapwel automatically
controls displaying of map objects like areas, lines and points at various
zoom levels. Zoom level of each object is based on the object's type.
For example, Major highways are visible in a larger scale than hiking
trails. Visibility of objects is also affected by number of objects
in the map. Maps with low number of objects are displayed at once, while
detailed maps
appear gradually as the user zooms-in the map.
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Other Resources listed at this site for Making your
own maps
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