| Online Store | Articles | SK Community | Advertisers | Contribute | Contact |
|
Navigation - February 2005 Digital Navigation for Kayakers If your dead reckoning is often dead wrong, computer-based resources can elevate kayak navigation to a higher level of accuracy and convenience. For the past few years, I’ve been using “digital navigation” on my sea-kayak trips. My spouse tells me “digital navigation” is when she points in the direction she wants to go and says, “Let’s paddle that way.” What I mean by “digital navigation” is using personal-computer, Internet and GPS resources to plan, undertake, enhance and review kayak trips. This article will explain why digital navigation can be useful for kayakers, let you see what can be done with digital navigation and direct you to resources. I will assume familiarity with navigation, map and compass, GPS, personal computers and the Internet. Resources cited here apply to the United States, but similar—sometimes superior—resources exist in Canada, Australia, New Zealand and Europe. Many of the resources described in this article can be modified to provide useful service in other regions. The focus of this article is on using digital navigation for sea kayaking, but because digital navigation has been evolving and expanding rapidly over the past few years, and to my knowledge, there are no primary or comprehensive information sources, this article will necessarily be incomplete and out of date. That’s the nature of our digital era. That having been said, this article should give you a good foundation in digital navigation and the resources to apply digital navigation to your own kayaking trips. As you consider how digital navigation can help you, you’ll need to decide what objectives are important to you, what computer resources, skills and aptitude you have, and how much time and money you wish to invest. Traditional Resources Traditional navigation is based on charts and maps—usually those produced by government agencies. “Charts” are nautical charts published by the National Oceanic and Atmospheric Administration (NOAA). “Maps” are topographic maps published by the United States Geological Survey (USGS). I like to use both charts and maps when kayaking. Charts show the undulations of the coastline better than maps. Charts show water depths, glacial moraines, underwater rocks and mud flats. This information is useful to predict areas of rough water, dangerous passage, unusual currents or long beaches. Charts show lights and other marine navigation aids, as well as shipping channels. Maps, on the other hand, are much better at showing topology, such as streams, valleys, glaciers, mountains and, to some degree, even vegetation. These landmarks can be very useful for identifying possible beaches or water sources and to correlate the topography on the map to the landscape around you while you’re kayaking. The section line grid is useful for estimating distances. When hiking, maps provide the information you’d need to find a route to a mountain peak or through a pass. Digital Resources Digital navigation is based on digital charts and maps, a computer with viewing software, and a GPS with a computer interface cable. Digital charts are produced by companies such as Maptech, which makes high-resolution scans from paper charts published by NOAA. These charts are “raster” charts, meaning that the scanned charts consist of millions of dots or “pixels” of color. They are “bitmap” images similar to photographs taken with a digital camera. SoftChart also produces charts that appear to be identical to the official NOAA charts except for their high-contrast color. Maptech and SoftChart sell charts for $15 apiece or for $150-$250 for a bundle that includes approximately 100 charts covering a large area, as well as other navigation resources for the region. SoftChart also lets users download individual charts for $9 and lower resolution portions of charts for $5. Because charts often cover a large area, you may find that only a few charts will fulfill your needs. Or, you may find it more efficient to purchase a package of charts for your main paddling area. Digital maps: The USGS creates digital maps by scanning paper maps at very high resolution, then resampling them and standardizing them as “digital raster graphics” (DRGs). The good news is that USGS DRG maps are available for free. Most states or regions have government agencies or universities that maintain geospatial libraries (including DRGs) that are available for download. DRGs also are available from commercial vendors. With a couple of clicks, it’s possible to download the .tif file (the digital map image), the .tfw file (which allows the map-viewer software to “georeference” the map image) and the metadata file (which provides lots of interesting information about how the map was created) for any DRG. One problem with downloading DRGs is determining which map you want for an area. You can identify the appropriate quadrangle using standard paper USGS index maps or search for this information on the Internet. Some download sources access DRGs using the quadrangle name, but some sources access DRGs using only the USGS’s file name for them. In that case, you may need to convert the quadrangle into the USGS’s file name for the DRG map. DRG file names aren’t very obvious. For example, the DRG map for Alaska, Seward D-5 1:63,360 is named i60148g5.tif. Once you know this file name, you can either download the map file from a DRG source, or do a Google search to find the official USGS metadata file. The “distribution” section of that file will direct you to the actual DRG file, which can be downloaded from the USGS. Beyond the awkward naming conventions of DRG files, the main problem with downloading DRGs is that the files are large. Downloads take a long time if you have a dial-up Internet connection. When uncompressed, each DRG consumes approximately 10MB of memory on your computer’s hard drive. Downloading DRGs is useful for initial or occasional digital map needs, but for ongoing digital navigation use, I’ve found it more efficient and convenient to purchase a set of maps from a vendor. My favorite source is AllTopo. A set includes all topographic maps for an entire state or group of states in one package. Finding and accessing particular maps within the set is fairly easy. The set for Alaska, for example, consists of 11 CDs of maps (containing over 3,000 maps) and costs less than $100. Viewing software: There are a number of programs that let you view and use digital charts and maps. I principally use OziExplorer, but other applications are available (included with the Internet resources on SK’s website—see link at end of article). Viewing programs generally cost less than $100. Bundled map packages and charts typically come with a viewer program, and free viewers are available. I decided it was best to learn and use one application rather than try to master several viewing programs. The commercial viewers generally have more features and capabilities than viewers included with bundled maps or available for free, but any of these applications may do all you want, and more. Because these programs generally deal with raster graphics in universal graphics formats, it’s generally possible to use a digital chart or map with any of these programs and to move charts and maps between these programs. With the viewing software, you can open a particular chart or map just as you would a digital photograph or other computer file. What you see on the screen looks exactly like a paper chart or map. Unlike a digital photograph or other graphic image, however, the chart or map is “georeferenced”: The software knows the latitude and longitude and Universal Transverse Mercator (UTM, a metric and non-angular global mapping system) coordinates for every point on the map and screen, using the correct “datum” and map projection. You can zoom in and out and drag the image to view the portion of the chart or map that interests you. (See Illustration 1.)
|
| NEXT > | LAST PAGE >> |