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Re: OZ .plt files into Magellan SD

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  • Trevor S
    ... Emphasis on looks like , using the beta of GPSBabel, the file it spits out (supposedly Meridan compatable) bears no resemblance to what a track
    Message 1 of 12 , Feb 1, 2004
      <Snip>
      > GPSBabel looks like it can read/write to the CD card:
      > http://gpsbabel.sourceforge.net/capabilities.html
      > Maybe there is a version that can also read/write Ozi
      > .plt files,

      Emphasis on "looks like", using the beta of GPSBabel, the file it
      spits out (supposedly Meridan compatable) bears no resemblance to what
      a track file on a Meridian SD card looks like.

      Looks like I will need to write my own... Only really tricky bit is I
      will need to code someting to work out the hex checksum on the end of
      each line, I just didn't want to re-invent the wheel !

      >or maybe you can use another program, such as G7ToWin.

      AFAIK, like Ozi it will only work directly with the GPS, which is time
      consuming, as I have 100's of tracks to convert ie OZI --> GPS --> SD
      Card and repeat several hundred times, as opposed to "convert all to
      SD" :)

      Cest la' vie !
    • eeronpoika
      ... what ... I ... of ... time ... SD ... If the Magellan file-format on SD-card is like below, you can use GeoConv to make the conversions between
      Message 2 of 12 , Feb 1, 2004
        --- In OziUsers-L@yahoogroups.com, "Trevor S" <trevor_s@b...> wrote:
        > <Snip>
        > > GPSBabel looks like it can read/write to the CD card:
        > > http://gpsbabel.sourceforge.net/capabilities.html
        > > Maybe there is a version that can also read/write Ozi
        > > .plt files,
        >
        > Emphasis on "looks like", using the beta of GPSBabel, the file it
        > spits out (supposedly Meridan compatable) bears no resemblance to
        what
        > a track file on a Meridian SD card looks like.
        >
        > Looks like I will need to write my own... Only really tricky bit is
        I
        > will need to code someting to work out the hex checksum on the end
        of
        > each line, I just didn't want to re-invent the wheel !
        >
        > >or maybe you can use another program, such as G7ToWin.
        >
        > AFAIK, like Ozi it will only work directly with the GPS, which is
        time
        > consuming, as I have 100's of tracks to convert ie OZI --> GPS -->
        SD
        > Card and repeat several hundred times, as opposed to "convert all to
        > SD" :)
        >
        > Cest la' vie !

        If the Magellan file-format on SD-card is like below, you can use
        GeoConv to make the conversions between SD-card-files and OZI. You
        can convert a set of files in one run, from file to file.

        $PMGNTRK,4743.481,N,12210.813,W,00038,M,131308.00,A,,160702*60
        $PMGNWPL,4611.052,N,12357.419,W,0000000,M,Ft-Stvns,,j*15

        Below a sample GeoConv-run:

        rem initialize parameters
        call geocoini.bat

        rem set input-parameters
        fvalue geoconv.infile=c:\gpsdata\magellan\sour\*.trk
        fvalue geoconv.inform=magellan

        rem set output-parameters
        fvalue geoconv.outfile=c:\gpsdata\ozi\dest\.plt
        fvalue geoconv.outform=ozitrk

        rem do the conversion
        geoconv

        You find GeoConv from Dave Pattons list of OZI third party utilities
        or directly from:

        www.iki.fi/eino.uikkanen/geoconvgb/

        Regards,
        Eino
        www.iki.fi/eino.uikkanen/
      • rwcx183
        ... what ... I ... of ... time ... SD ... The hex checksum is pretty easy to generate, but before you go to the trouble, make sure that you need to. Some
        Message 3 of 12 , Feb 1, 2004
          --- In OziUsers-L@yahoogroups.com, "Trevor S" <trevor_s@b...> wrote:
          > <Snip>
          > > GPSBabel looks like it can read/write to the CD card:
          > > http://gpsbabel.sourceforge.net/capabilities.html
          > > Maybe there is a version that can also read/write Ozi
          > > .plt files,
          >
          > Emphasis on "looks like", using the beta of GPSBabel, the file it
          > spits out (supposedly Meridan compatable) bears no resemblance to
          what
          > a track file on a Meridian SD card looks like.
          >
          > Looks like I will need to write my own... Only really tricky bit is
          I
          > will need to code someting to work out the hex checksum on the end
          of
          > each line, I just didn't want to re-invent the wheel !
          >
          > >or maybe you can use another program, such as G7ToWin.
          >
          > AFAIK, like Ozi it will only work directly with the GPS, which is
          time
          > consuming, as I have 100's of tracks to convert ie OZI --> GPS -->
          SD
          > Card and repeat several hundred times, as opposed to "convert all to
          > SD" :)
          >
          > Cest la' vie !

          The "hex checksum" is pretty easy to generate, but before you go to
          the trouble, make sure that you need to. Some GPS receivers, though
          they do generate the checksums for data that they send, they don't
          require them for data they receive. Probably a quick test would
          establish the answer. If you do need to generate the checksums, then
          just do an XOR of all of the chars between the $ at the beginning of
          the sentence and the * at the end of the sentence. Don't include the
          $ or *. After that, convert the result to 2 ascii digits and append
          it to the sentence.

          J.G.

          P.S. What DOES the file that GPSBabel spits out, look like?
        • rwcx183
          ... UTM ... calibration ... Greg, I agree that it is possible to export a tfw file in decimal degrees, if the original map image is in lat/lon projection.
          Message 4 of 12 , Feb 4, 2004
            --- In OziUsers-L@yahoogroups.com, "Greg Harewood" <explorer@v...>
            wrote:
            >
            > Dave, emailed you ages ago about this but obviously got lost in
            > limbo - please add to your info on tfw.dat that it is possible to
            > export a tfw file in decimal degrees (not just metres) if your map
            > is calibrated using the Lat/Long Map projection. If you require
            > decimal degree output and your map is calibrated in metres using
            UTM
            > there is no need to recalibrate the entire map using degrees and
            > lat/long ...just change the Map Projection used in the calibration
            > from UTM to Lat/Long, save and then any resulting tfw files created
            > will be in decimal degrees. You can then change your map
            calibration
            > back to UTM when you are finished with no harm done. The map image,
            > as mentioned in the list, must be "square" (i.e. lat/long or E/N
            > lines must be parallel) with no rotation if you are chasing a
            > perfect result.
            > Cheers
            > Greg

            Greg,

            I agree that it is possible to export a tfw file in decimal degrees,
            if the original map image is in lat/lon projection. Temporarily
            changing the map cal projection from UTM to lat/lon, so that the .tfw
            file units will be in degrees, doesn't exactly work correctly. This
            is because of some implicit assumptions about .tfw files in general.
            The first assumption is that the image is rectified. That is, there
            is a simple transform from pixel coordinates to the given coordinate
            system. This assumption would not be true for an image that is
            rectified and projected to UTM coordinate system and then the
            reference points and scale values in the .tfw file are changed to
            decimal degrees. It may be true that such a .tfw file along with
            it's
            companion image file, will import correctly into OziExplorer, but the
            world of mapping programs that can read/import .tfw/image file pairs,
            is much larger than the tiny little corner occupied by OziExplorer.
            Of the couple dozen mapping programs other than OziExplorer, that I
            have, not a one of them can handle a UTM projected image with it's
            companion .tfw file in units of degrees. The underlying reason, is
            that there is a fundamental difference between true north and "grid
            north" on the UTM coordinate system. An image that is perfectly
            square to UTM grid, with grid north straight up and down, is most
            definitely not aligned to true north. The one exception to that, is
            if the image is precisely at the center of a UTM zone. That is the
            only place where UTM grid north and true north are the same.
            Everywhere else, there's a difference known as "grid convergence".
            That the two are different, means that there is not a simple
            transform from pixel coordinates to lat/lon coordinates.

            To sum it up, exporting a .tfw file in units of degrees, by changing
            the cal/projection to lat/lon, for a UTM rectified image, will
            produce a .tfw file that Ozi maybe can use for subsequent
            importation, but
            such a .tfw file is useless to most if not all, other mapping program.

            J.G.
          • Greg Harewood
            ... to ... map ... calibration ... created ... image, ... degrees, ... the .tfw ... This ... general. ... there ... coordinate ... the ... pairs, ...
            Message 5 of 12 , Apr 16, 2004
              --- In OziUsers-L@yahoogroups.com, "rwcx183" <lgalvin@p...> wrote:
              > --- In OziUsers-L@yahoogroups.com, "Greg Harewood" <explorer@v...>
              > wrote:
              > >
              > > Dave, emailed you ages ago about this but obviously got lost in
              > > limbo - please add to your info on tfw.dat that it is possible
              to
              > > export a tfw file in decimal degrees (not just metres) if your
              map
              > > is calibrated using the Lat/Long Map projection. If you require
              > > decimal degree output and your map is calibrated in metres using
              > UTM
              > > there is no need to recalibrate the entire map using degrees and
              > > lat/long ...just change the Map Projection used in the
              calibration
              > > from UTM to Lat/Long, save and then any resulting tfw files
              created
              > > will be in decimal degrees. You can then change your map
              > calibration
              > > back to UTM when you are finished with no harm done. The map
              image,
              > > as mentioned in the list, must be "square" (i.e. lat/long or E/N
              > > lines must be parallel) with no rotation if you are chasing a
              > > perfect result.
              > > Cheers
              > > Greg
              >
              > Greg,
              >
              > I agree that it is possible to export a tfw file in decimal
              degrees,
              > if the original map image is in lat/lon projection. Temporarily
              > changing the map cal projection from UTM to lat/lon, so that
              the .tfw
              > file units will be in degrees, doesn't exactly work correctly.
              This
              > is because of some implicit assumptions about .tfw files in
              general.
              > The first assumption is that the image is rectified. That is,
              there
              > is a simple transform from pixel coordinates to the given
              coordinate
              > system. This assumption would not be true for an image that is
              > rectified and projected to UTM coordinate system and then the
              > reference points and scale values in the .tfw file are changed to
              > decimal degrees. It may be true that such a .tfw file along with
              > it's
              > companion image file, will import correctly into OziExplorer, but
              the
              > world of mapping programs that can read/import .tfw/image file
              pairs,
              > is much larger than the tiny little corner occupied by
              OziExplorer.
              > Of the couple dozen mapping programs other than OziExplorer, that
              I
              > have, not a one of them can handle a UTM projected image with it's
              > companion .tfw file in units of degrees. The underlying reason,
              is
              > that there is a fundamental difference between true north
              and "grid
              > north" on the UTM coordinate system. An image that is perfectly
              > square to UTM grid, with grid north straight up and down, is most
              > definitely not aligned to true north. The one exception to that,
              is
              > if the image is precisely at the center of a UTM zone. That is
              the
              > only place where UTM grid north and true north are the same.
              > Everywhere else, there's a difference known as "grid
              convergence".
              > That the two are different, means that there is not a simple
              > transform from pixel coordinates to lat/lon coordinates.
              >
              > To sum it up, exporting a .tfw file in units of degrees, by
              changing
              > the cal/projection to lat/lon, for a UTM rectified image, will
              > produce a .tfw file that Ozi maybe can use for subsequent
              > importation, but
              > such a .tfw file is useless to most if not all, other mapping
              program.
              >
              > J.G.

              J.G
              The method I suggested is of course inaccurate if the map is not
              rectified and as you mentioned it is not likely a map would be
              rectified in both UTM and Lat/Long. The main reason I mentioned it
              is to make it known that you can create a tfw file in decimal
              degrees if required - a fact not mentioned in the information
              currently available on the tfw.dat function.

              Also the method is in fact useable for unrectified images despite
              your claim to the contrary. I recently created tfw files for a
              series of unrectified ecw maps that I wanted to view with erviewer.
              Because this program only reports to two decimal degrees an
              inaccurate tfw file was of no concern (well it wasnt to me). If you
              require a high degree of accuracy the method is not much
              chop..agreed.

              Cheers
              Greg
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