Garmin Custom Maps

[nfennie]

I have been making a number of custom maps from PDF files that I have acquired over the years. Some people have commented on how hard it is to get the maps to match the satellite image in Google Earth. This may actually be due to an inaccurate source map.

 

What I am finding is that once I have the map overlayed correctly (using at least 3 prominent landmarks, the custom map features may be significantly off. This is most like due to the original map maker's inaccuracies, especially if after making a track (by GPS signal) and then overlaying it in GE along with the custom map overlay, the Satellite image and the GPS agree, but not the custom map, guess who is right?

 

A guess this means that someone should create a GPSr that pulls in a live image from GE as well as a GSP signal.

 

There is a market opportunity in there for someone.

[+user13371]

You mean like any GPS-equipped smartphone already does?

[MikeToCache]

You may need to read about 'map projections' to understand the issues with getting your maps to line up. If your maps are all done with different map projections and datum then they will have issues like you describe.

[nfennie]

You mean like any GPS-equipped smartphone already does?

 

Yes, but with all of the other features that a GPSr has, geocahing, topo maps, etc. Maybe it's the Nuivphone? Haven't looked at that device in any detail.

[+user13371]

At the risk of setting off the usual feeding frenzy... iPhone has the all of the specifics you requested. And even carrying a dedicated GPS, a lot of folks like the iPhone as a secondary device because nothing else handles the "paperless" aspect better.

 

In an attempt to preempt one of the frequent misconceptions offered here: The iPhone's GPS does work when you're out of cell-phone range and you can also preload road and topo detail maps for such offline use.

 

And admitting some of its shortcomings: The iPhone is not designed foir outdoor/rugged use, nor is it waterproff. It runs down its battery very fast and you'd have to carry spares in an external pack, and the GPS accuracy is more suited to finding cafes than caches.

 

I'd write more, but I'm heading out the door in a few minutes with both my iPhone and my "real" GPS in my coat pocket.

 

I'm sure the arguments will be well in progress by the time I get home this afternoon. Carry on...

Edited December 13, 2009 by lee_rimar

[mtbikernate]

+1 on learning about map projections and georeferencing. 3 landmarks isn't nearly enough for a good georeferenced image. I usually try for at least a dozen, and they need to be from different parts of the image for it to work. You know, stuff from each corner, various spots in the middle, etc. you see, I'm not sure how much control you have over the process the way you're doing it. but with few points, only certain corrections can be made on the image. the more points you add, the better corrections that can be applied, and the better your final output is.

 

the software I use for georeferencing (ArcGIS) tells me how much a given reference point is helping or hurting the overall process, so I can change them, delete bad ones, etc.

 

with the right software (and the right person doing it), the process is EXTREMELY accurate. I have put these images onto ArcPad (windows mobile program) and the GPS coords are spot-on.

[snomchfun]

The key to getting your maps to fit from GE is when you open up the add overlay dialog go to the altitude tab and change "clamped to ground" to "absolute". My GE satellite maps on my Oregon are in perfect sinc with my gps data.

[+gelfling6]

I'm finding this as well, trying to line-up maps scanned into my computer (using an HP All-In-One unit.) and using a program called MyGPS (Link to MyGPS Home Page), and trails from the Connecticut Forrest & Parks Walk books. It only offers 2 points to calibrate the map.. It's crude at best, but I've used it to trace-out a few blazed trails, and overlay it to a few navigation mapping programs I have on my laptop. (I.E. Garmin MapSource, DeLorme Street Atlas USA, and Even Microsoft Streets & Trips.).

 

I ran into another program, from Microsoft, of all things, called MSR MapCruncher . Which allows for more calibration points, and tells the accuracy once the points are placed. But, MSR mapCruncher has a non standard data output. But it compares a raster map (which you place the calibration points on) to a BING Satellite image.

 

Also, You've got to remember, a lot of the road & trail maps were written either before, or with just GPSr readings. the physical road/trail locations are bound to be different.

 

Stephen (gelfling6)