GPS Pilot: Scanned maps Conversion
          
      Scanned maps
      info@GPSpilot.com  
      Scan and import paper maps (wrote by Don Maxwell, many thanks to his 
      tribute)
      SECTIONAL CHARTS. I've been experimenting with scanning sectional charts 
      to use with Atlas.  I've tried a lot of different scan resolutions, trying 
      to figure out which is the best resolution and how much of a chart is best 
      to scan.
      Black and white scanning at 100 dots per inch seems to be the most 
      practical scan resolution to use.  If you decide to begin collecting 
      sectional chart submissions from Atlas owners, this might be the best scan 
      resolution to use as a standard.  Here's why I think so:
      COLOR.  I've tried scanning in color and gray scale, but both require a 
      lot of work to produce a useable two-color bitmap.  (I don't have a Palm 
      III, so I can't test gray scale maps in Atlas.)  Black and white scans are 
      simple, and they seem to work reasonably well on sectional charts.  I'm 
      using a Microtek Scanmaker E6 and PhotoImpact software.
      RESOLUTION.  The Palm display is 160 x 160 pixels, and it's about 2 3/16 
      inches wide and high.  (That's about 56 mm, but my scanner software uses 
      dots per inch.)  That works out to approximately 73 pixels per inch in the 
      display, but scanning at that resolution is too coarse for small text to 
      be readable.  Scanning at 146 or 147 dpi double the Palm Pilot display 
      resolution produces very nice results, but the image is larger than 
      necessary for legibility, and of course it consumes more Palm memory.  At 
      100 dpi, however, most text is legible and most map features show up 
      reasonably well.   (Scanning at 110 dpi is 150% of 73, which also reduces 
      pixelization, but it isn't significantly better than 100 dpi.)  
      Furthermore, 100 dpi is convenient in Atlas, because the scale of the map 
      is about 11 nautical miles, or about 20 km, across the Palm screen easy 
      numbers to remember.
      EXAMPLE.  Here's a 300 dpi scan of my Palm Pilot Pro displaying an Atlas 
      view of the Petersburg, Virginia, airport.

      As (I hope) you can see, it's not a really sharp image, but most of the 
      text is legible, and most landscape features are recognizable, including 
      the magenta class E airspace around the airport.  If you look closely, you 
      can even read the CTAF and AWOS frequencies.
      The scale is about 150% of the actual sectional chart.  That's bigger than 
      I'd like, but so far I haven't been able to produce bitmaps below 100 dpi 
      that are useful in the Palm Pilot.
      Here's the actual bitmap of that portion of the map (you should see it 
      doubled in size here): 
      The entire map in this scan covers 2 degrees of longitude and 2.9 degrees 
      of latitude.  It's 648x773 pixels and 63,289 bytes--and it fits into 
      Cartographer and Atlas! (I have a TRG 2+2 meg RAM card.)  I made it so 
      large because it covers the entire area surrounding the airport from which 
      I normally fly.
      SCAN AREA.  The projection in sectional charts is such that the lines of 
      latitude are parallel, but the lines of longitude are not.  Therefore, the 
      larger the area scanned, the greater the location error there will be in 
      Atlas.  For that reason, I think it's best to scan no more than one or two 
      sectional chart grid rectangles at a time.  This keeps the error to a 
      minimum.  I've found that scanning two horizontal grid rectangles is a 
      good compromise--at least at the latitude where I live, in Virginia.  The 
      rectangles are higher than they are wide, so two side by side makes a map 
      that is more or less square and is a convenient size for Cartographer and 
      Atlas.  Side by side rectangle-pairs contain less error than vertical 
      rectangle-pairs do.
      However, scanning one grid rectangle at a time (at this latitude) produces 
      even smaller errors, especially at higher latitudes.  Also, individual 
      grid rectangles might be easier to keep track of in a database.  They 
      could be identified by latitude and longitude numbers, such as 37.0&37.5, 
      -77.0&-77.5 or some similar scheme.
       
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