Garmin GPS Extension
|
Current
Version ArcView
Extension: 3.0
VB Program: 1.2.4 Build Date:
3/15/2002 Posted Date: 4/11/2002 Platform/ArcView Version
Dependencies ESRI - Dialog Designer Extension Internet Explorer 5.0 or higher. Garmin Communications using pcoGarmin by Ron Whately. http://www.c-nav.com |
Purpose of this Extension Frequently Asked
Questions This extension was built to provide users the ability to directly transfer data between ArcView GIS and a Garmin GPS handheld receiver. Using this extension a user can take polygon or line shapes in ArcView, create a track log and upload to the GIS Unit.
This extension has a real-time tracking mode that allows users to follow their progress on the ground within an ArcView View document. This real-time track log can be saved as either points or lines as a set of graphics or in a shapefile.
At this time this extension contains the
following functionality.
Planned UpgradesThe
ability to transfer and manage route data. |
For track logs, each Garmin Unit
has a different amount of memory to store coordinates. If you select polygons
or lines to convert to a track log the extension will check to see how many vertices
are in the selected shapes. If the number of vertices is greater than the
number of points that the unit can store in a track log, then the extension
will weed the vertices, based on a user supplied tolerance, using the
Douglas-Poiker algorithm until the number of points is below the threshold.
Question – I have my Garmin unit set to display
coordinates in UTM, NAD83 Datum but when I look in the DNR Garmin window they still
show the coordinates in Decimal Degrees? What gives?
Answer
– On Garmin GPS’s when transferring waypoints and tracks the
coordinates are always downloaded as Lat/Longs in Decimal Degrees based on the
WGS84 Datum no matter how the display units are set in the GPS.
Question – I’m confused
about how DNR Garmin handles projections.
Answer – As stated
above, when coordinates
are transferred from the Garmin GPS they are expressed as Lat/Long in decimal
degrees, WGS84 Datum. When data is transferred to and from ArcView, the data is
projected (to ArcView) or unprojected (to the GPS) they are projected on the
fly using the projection you define using the DNR Garmin | Set Projection menu
option. The first time you use the program you will be asked if you want to use
the default projection which is set to UTM Zone 15, NAD 83 Datum (this is the
MN DNR Standard). If you choose NO to this query, you will be presented with
the ArcView Projection Definition Dialog so that you can tell the extension
which projection you want to use. It will then store this information in a file
that is used in future upload/download process. You can reset the projection at
any time by using the DNR Garmin | Set Projection menu option.
This process makes the assumption
that you're base data (existing data you are comparing the GPS data to) is
projected and is being displayed in an unprojected View.
For those users who's data is in
Geographic Coordinates and they are using a "Projected View" this is
where the problems start. Many times users mis-interpret the DNR Garmin query
for projection and enter their view projection parameters at this point. The
problem at this point is that the data is first being projected to the
coordinate system they entered and then, ArcView is projecting the data again
because it's putting the data into a Projected View.
If you're base data is in Geographic
Coordinates, then you need to specify Geographic Coordinates as the projection
system as Geographic listed under the Projections of the World Category.
Question – Why do the coordinates always show
up as Lat/Long in Decimal Degrees in the DNR Garmin VB Program?
Answer – The Garmin Extension is actually a
combination of an ArcView Extension (DNRGARMIN.AVX) and a Visual Basic (VB)
program (DNRGARMIN.EXE). The VB program is the middleware between ArcView and
the Garmin GPS. It provides the capability to use the com port for
communications to and from ArcView to the GPS. Since this program was designed
around ArcView it was decided to use ArcView’s native projection engine rather
than build one ourselves.
When
you install the DNR Garmin extension the first prompt you will see is where to
install the extension. If you are part of the Minnesota DNR use the default
value. If you are not a Minnesota DNR Employee you will need to change the
installation location to the folder where ArcView accesses extensions.
Typically this is \ESRI\AV_GIS30\ARCVIEW\EXT32.
You
will then have the option of doing a Typical Install or a Compact
Install. Which type of install you choose depends on your desktop
computer environment. For example, in the Minnesota DNR we have offices that
have networks and those that don’t. In offices where there is a network, all of
the ArcView users access extensions via a shared network folder. If this is the
case only the system files need to be installed on your computer so the Compact
Install works for you. In offices where there is no network and all
machines are stand-alone, then choose the Typical Install option.
Typical
Install – Use this option when you don’t access your extensions across a
shared network drive or you want to use the real-time tracking options outside
of the office.
Compact
Install – Use this option when you are in a networked location where all
ArcView extensions are accessed via a shared network location and you don’t
plan on using the extension outside of the office.
DOWNLOAD
DNRGARMIN_SETUP.ZIP
- Full Extension with Documentation
(4.0 mb)
4/11/02
– Version: DNRGarmin.AVX – 3.0, DNRGarmin.exe – 1.2.4
Changes:
1)
Internal changes to AVX and EXE to avoid conflicts with other
ArcView Extensions that use DDE.
2)
New DNRGarmin_Setup.EXE file that provides both the Typical and
Compact installation options in one file.
3)
Now converts from WGS84 to NAD27 on the fly using NADCON compliant
code compliments of Mark Cederholm.
4)
Fixed Date fields on tracks and waypoints.
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