We have pretty extensive coverage in Southern New Jersey with USGS NED 1/9 arc second LIDAR DEM, so I'm trying to find a way to use this in a map. It's especially nice around here where everything is so flat because it reveals a lot of surface detail in the forest.
It would be very easy to make a garmin "custom map" (.kmz raster image) from this data, but it's pretty limiting both in size and in the number of devices that can use it. So my thought was to vectorize it using Globalmapper's function to create polygons based on RGB values.
I have all the data, so for starters I cropped it to the outline of the map I want to make, then exported it as gridded 8 bit grayscale TIFF's that are ~500x500 pixels. Globalmapper converts these into anywhere between 50,000 to 60,000 polygons when using a match distance of 16. Smaller values for match distance create way too many polygons.
Here's a comparison of the original TIFF to the vector image. Globalmapper really does a great job - it's hard to tell them apart until you zoom way in.
Next I export a shapefile and use Filemaker Pro to do some processing of the .dbf, parsing the RGB values and mapping them to MP_TYPES in a custom .typ file. I decided to go this route instead of using a program like MOAGU or Mapwel because it gives me full control over everything.
I then import the modified shapefile back into Globalmapper, combine with other vector features like roads, then export an .mp file to compile with cgpsmapper. My current prototype breaks a USGS 24k quad into 8x8=64 tiles, each of which is ~1MB. So far so good. Here's what it looks like in Globalmapper
And the compiled map in Mapsource looks surprisingly good - bet ya didn't think Mapsource could do this!
But then the fun begins... there are two problems on the GPS. First, it practically brings the unit to its knees due to all the little polygons (I tried on a Nuvi 205 and Montana 600). But worse, the GPS doesn't seem to render the image with as much precision as Mapsource, even with detail set to max. Basically, it's a mess. Kind of an interesting abstract art image, but nothing like the original.
So I'm going to need to re-think this and do more experimentation.
Anyway, it's an interesting although time consuming and sometimes frustrating project that I wanted to share. I have also recently refined my technique for processing the Landsat NLCD 2006 landcover data in a similar fashion and that is working out really well - but that source imagery is about 10 meters pixel. I'll post some details about this in another thread soon.
Hope everyone is enjoying the holidays - here's wishing a happy New Year to all!