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Re: USNF User Maps

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  • Bill Davison
    I m just starting to play with this - my quest is to get detailed national forest boundaries onto my Garmin GPS, which led me to buy Ozi a couple weeks ago.
    Message 1 of 4 , Oct 1, 2006
      I'm just starting to play with this - my quest is to get detailed national
      forest boundaries onto my Garmin GPS, which led me to buy Ozi a couple weeks
      ago. Seems like the only way is to trace the boundaries in Ozi. Anyway, I
      found free USFS vector and raster images at 1:24000 here:

      http://svinetfc4.fs.fed.us/

      What follows are some notes on how I've been importing them. Feel free to
      ignore if you're an experienced user. Thought it might be useful for other
      newbies like me, since I burned quite a few hours figuring it out.

      Raster seems to be what you want for Ozi. The files on the USFS site are
      compressed in TAR format - WinZip was able to handle it without any
      problems. The download will have 2 versions - uncollared is just the map,
      collared has the stuff you'd normally see on the white border of a printed
      topo. I've had better luck importing the uncollared maps. In Ozi, I start
      with Map/Blank Map, then do File/Import Map/Single DRG Map. Got stuck on
      the datum - the metadata supplied on the USFS website says "North American
      Datum of 1927" - but Ozi has several NAD27 choices. The forest service maps
      are based on USGS topos, and as best I can tell from digging around online,
      the right answer for those is "NAD27 CONUS". As a new user I also got burnt
      by the calibration thing - I would trace a boundary in Ozi, and the line I
      drew would display in Ozi, but it would be an inch or two off from where I
      thought I had put it. Problem solved when I calibrated using the corners of
      the map - the lat/long of the corners are displayed on the collared version,
      which opens in Microsoft Office Document Imaging when I double-click the
      TIF.

      I'd be interested to hear tips from anyone who's doing it differently.

      Bill


      --- In OziUsers-L@yahoogroups.com, "hrs_o1" <hrs_o1@...> wrote:
      >
      > Does anyone know of a source for scanned national forest maps for the
      > USA?
      >
      > Thanks, Harold
      >



      [Non-text portions of this message have been removed]
    • rwcx183
      ... national ... couple weeks ... Anyway, I ... free to ... for other ... site are ... the map, ... printed ... I start ... stuck on ... American ... service
      Message 2 of 4 , Oct 1, 2006
        --- In OziUsers-L@yahoogroups.com, "Bill Davison" <wdavison@...>
        wrote:
        >
        > I'm just starting to play with this - my quest is to get detailed
        national
        > forest boundaries onto my Garmin GPS, which led me to buy Ozi a
        couple weeks
        > ago. Seems like the only way is to trace the boundaries in Ozi.
        Anyway, I
        > found free USFS vector and raster images at 1:24000 here:
        >
        > http://svinetfc4.fs.fed.us/
        >
        > What follows are some notes on how I've been importing them. Feel
        free to
        > ignore if you're an experienced user. Thought it might be useful
        for other
        > newbies like me, since I burned quite a few hours figuring it out.
        >
        > Raster seems to be what you want for Ozi. The files on the USFS
        site are
        > compressed in TAR format - WinZip was able to handle it without any
        > problems. The download will have 2 versions - uncollared is just
        the map,
        > collared has the stuff you'd normally see on the white border of a
        printed
        > topo. I've had better luck importing the uncollared maps. In Ozi,
        I start
        > with Map/Blank Map, then do File/Import Map/Single DRG Map. Got
        stuck on
        > the datum - the metadata supplied on the USFS website says "North
        American
        > Datum of 1927" - but Ozi has several NAD27 choices. The forest
        service maps
        > are based on USGS topos, and as best I can tell from digging around
        online,
        > the right answer for those is "NAD27 CONUS". As a new user I also
        got burnt
        > by the calibration thing - I would trace a boundary in Ozi, and the
        line I
        > drew would display in Ozi, but it would be an inch or two off from
        where I
        > thought I had put it. Problem solved when I calibrated using the
        corners of
        > the map - the lat/long of the corners are displayed on the collared
        version,
        > which opens in Microsoft Office Document Imaging when I double-
        click the
        > TIF.
        >
        > I'd be interested to hear tips from anyone who's doing it
        differently.
        >
        > Bill

        The problem with the USFS maps is that although they're rectified and
        fully georeferenced to the UTM coordinate system, the Forest Service
        has not provided them in a non-rotated form. That is, despite not
        embedding the georeferencing data within the .tif file itself,
        the .tfw file is specifying rotation/translation for the axes.

        2.43821350156848
        -0.04957878608911
        -0.04933228222783
        -2.43822674772635
        303490.69635168235982
        3821166.33178112842143


        While that is technically allowed per the ESRI specification
        of "world" files, few non-pro mapping programs support that.
        OziExplorer is not one of them. So, if you want to use these images,
        you'll have to sink to the dirty deed of manual calibration. Not
        hard, but to be avoided on philosophical grounds.

        Nobody should fret over the exact version of NAD27 they're using,
        since there isn't much difference, so long as you stick to one that
        applies to the region of which your map images cover. Ie, NAD27
        Alaska, if your map image coverage is in Alaska. NAD27 ConUS
        otherwise. Don't be tempted by NAD27 Central, as that actually
        refers to Central America, in which the U.S. does not yet have any
        National Forests ;-) Technically, there is just one NAD27 datum.
        It's in Kansas somewhere, but it was defined in the pre-GPS era and
        it represents a somewhat distorted view of the continent. So, there
        are numerous translations from NAD27 to WGS84 defined in an effort to
        minimize error for a given local area. Use the one that is best for
        the area of interest.

        J.G.
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