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Author Topic: do I need to re-project data to WGS84 for Garmin GPS  (Read 871 times)

RCinSTP

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do I need to re-project data to WGS84 for Garmin GPS
« on: August 06, 2017, 05:50:24 AM »
When I make a map for Garmin GPS, do I need to begin with data that has a Coordinate System of WGS84?

-Oz-

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Re: do I need to re-project data to WGS84 for Garmin GPS
« Reply #1 on: August 06, 2017, 11:26:35 AM »
That would be best but most data is already in WGS84/NAD83 which work "out of the box"
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Pooneil

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Re: do I need to re-project data to WGS84 for Garmin GPS
« Reply #2 on: August 26, 2017, 05:23:30 PM »
When I make a map for Garmin GPS, do I need to begin with data that has a Coordinate System of WGS84?
Some raster data, such as geo-located park trail maps, use a mercator projection, (it's not a coordinate system) and must be converted into WGS 84 to be used on a GPS.  The only way I know how to do this is in a mapping program like QGIS. 

MojaveMan

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Re: do I need to re-project data to WGS84 for Garmin GPS
« Reply #3 on: August 30, 2017, 07:07:56 AM »
I do re-project my "raster" maps using a complex process involving a free graphics manipulation program: imagemagick.
The vast majority of the maps I make are Garmin Custom Maps - and for some reason most of the maps I download (USGS topo, park maps available online) are in a different projection such that things are terribly askew with the Garmin Custom Maps.  Fortunately, they have some guide marks on them (16 of them for the USGS topo maps) that show where the LAT/LON are supposed to be.
There is a manual process by which I find these hash marks and use imagemagick to force them into a proper grid.  Imagemagick takes my measurements and shifts every pixel on the map according to a 5th order polynomial in order to minimize distortions across the entire map.  After I use this process, I then put the shading in (which, for some reason, is provided in the proper projection).  I wrote a script to simplify this process.

I'm sure there is an easier way with something like GRASS GIS, but my chosen method seemed the path of least resistance with what knowledge I already had.

Boyd

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Re: do I need to re-project data to WGS84 for Garmin GPS
« Reply #4 on: August 30, 2017, 07:27:00 AM »
I still use my old version of GlobalMapper (the new version has gotten expensive and has restrictive licensing). These projection issues are trivial, just a few mouse clicks to re-project into anything you want. I use quite a bit of data from my state (NJ) and it is frequently in state plane format. Globalmapper opens anything and I set a preference for WGS84, so whatever I export is automatically set for that.

However, long term I'm trying to decide if qGIS can meet my needs since it is free open source and looks pretty good. Pretty sure it can easily re-project too. Check it out if you haven't already, but be prepared for a pretty steep learning curve if you're used to consumer software like Garmin's. ;)

http://www.qgis.org/en/site/

jolly47roger

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Re: do I need to re-project data to WGS84 for Garmin GPS
« Reply #5 on: August 30, 2017, 12:08:59 PM »
Reprojection is only relevant to Raster data as Vector data has no associated projection.

Reprojection is one of the functions I incorporated into MAPC2MAPC.

popej

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Re: do I need to re-project data to WGS84 for Garmin GPS
« Reply #6 on: August 31, 2017, 02:59:12 AM »
However, long term I'm trying to decide if qGIS can meet my needs since it is free open source and looks pretty good. Pretty sure it can easily re-project too.
QGIS is a very useful program but a bit buggy. It can reproject maps.

Other tools for this task are command line tools like GDAL. It is bundled with QGIS distribution, so the easiest way to get this working is to install QGIS.
http://www.gdal.org/gdalwarp.html
http://www.gdal.org/ogr2ogr.html

Reprojection is only relevant to Raster data as Vector data has no associated projection.
All Garmin maps are WGS84, but vector data in general do have projection, which should be converted to WGS84 for creating maps for Garmin.

RCinSTP

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Re: do I need to re-project data to WGS84 for Garmin GPS
« Reply #7 on: September 06, 2017, 07:42:46 AM »
Thank you all for your helpful advice.  Boyd, regarding Global Mapper, it is a great mapping program, very nice, very useful, too bad it is way too expensive, maybe that's why there are so many "hacked/free" version available on Torrent websites.  If it wasn't soo expensive, people wouldn't make hacked fully working versions of Global Mapper available. Some of them are a couple of versions old, not the most recent version but they have everything you need to make great maps.

Boyd

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Re: do I need to re-project data to WGS84 for Garmin GPS
« Reply #8 on: September 06, 2017, 08:03:23 AM »
If it wasn't soo expensive, people wouldn't make hacked fully working versions of Global Mapper available.

It really is too bad. Globalmapper was very popular around here "back in the day", that's what got me started. Here's an article about it from the (now defunct) cgpsmapper website for example: https://web.archive.org/web/20120310083822/www.cgpsmapper.com/download/GM8DocV2.pdf

I think it was about a $300 program back then. I went through maybe 3 upgrade cycles. Then it was bought by Blue Marble and got more and more expensive. Aside from the cost, this is what really puts me off with the current version.

"The Single Machine node lock license is licensed to a single computer only. Re-authorization provided only if software removal verification can be provided by customer. Customer system upgrades require un-installation verification prior to new licenses being issued. "

As a hobbyist, I can't afford to upgrade frequently and have moved my old copy across three different machines when I replaced my hardware. This new policy seems to depend on their whim, and when a version gets too old they can prevent you from authorizing it on another machines. And how to you verify to their satisfaction that the old copy has been removed?

I guess this is just the way of the world though. I started using a CAD package called MiniCAD back in the 1990's. It was probably the most powerful Mac CAD software at that time and cost around $350. It is now called VectorWorks and was bought by a big German corporation - prices just kept going up. Just found that my 2008 version will no longer run on the newest Mac operating system. I paid $1300 for that, which seemed expensive at the time. Of course, it's too old to qualify for upgrade pricing and the new version is about $2500. Ridiculous! I'm retired and don't need it a lot, but I still need something. So I keep one machine set up for dual booting into a legacy operating system for that.

Same thing is happening in both of these examples though. GlobalMapper was purchased by a big company that is no longer interested in the low end of the market and is now trying to compete with ArcGIS. VectorWorks is just the same, instead of a low cost CAD alternative, now they try to compete head on with AutoCAD.

Sorry for the rant, but this kind of stuff is very frustrating. ;)
« Last Edit: September 06, 2017, 08:05:25 AM by Boyd »

jolly47roger

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Re: do I need to re-project data to WGS84 for Garmin GPS
« Reply #9 on: September 07, 2017, 06:49:14 AM »
I sell MAPC2MAPC for $20 - but I have still had to put in a lot of work to stop hacking and the generation of fake codes. Being cheap is no protection!

Boyd

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Re: do I need to re-project data to WGS84 for Garmin GPS
« Reply #10 on: September 07, 2017, 07:09:09 AM »
Hey... maybe a big company will buy it, add a whole bunch of features we don't need and raise the price to $1250? ;)

 

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