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Image Resolution for Garmin upload

Started by The Foster Bear, January 02, 2012, 01:17:45 PM

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The Foster Bear

The local preservation society has purchased a Garmin GPSmap 62 cs. The primary use is to locate and document historic cemeteries and ruins in the town. We are only 54 square miles but have 148 documented historic cemeteries. My problem is in securing a good Topo map of the town. We are in 4 grids so the maps need to be stitched together to make a single map. A Topo map is important because we are rural and have a lot of wet land. Thus traveling is difficult without knowing what the terraine is. Base camp will only allow me to load a maximum of a 1 megapixel image which is so small that any definition is lost. Any suggestions for a work around? We really can't afford to buy the map packages and what comes on this unit is worthless for our purposes.

Thanks, The Foster Bear


You don't give your location.  Where is your town?
Have you looked at the state topo maps available on this site?  Many of them include wetlands.  Most are 24k topos (USA), that is the quality of the USGS 7.5' Quadrangle maps.


Quote from: The Foster Bear on January 02, 2012, 01:17:45 PMBase camp will only allow me to load a maximum of a 1 megapixel image which is so small that any definition is lost

Actually, that is not true. 1024x1024 is the maximum size of a SINGLE TILE within a .kmz file. You can have a total of 100 tiles of this size within the .kmz. You will want to use some software to help construct such a map. Have a look at mapc2mapc, g-raster and mobile atlas creator for starters.

If you like the USGS 24k topo's, you can get unlimited downloads of them by purchasing Birdseye Topo. As a practical matter, there really isn't any limit to the size of this map that you can use, as long as it fits on your memory card:

For $30 I think this is a very good deal. Register your 62s at Garmin you you will get a 10% discount code, bringing the cost to $27.

The Foster Bear

Thank you for your quick replys.

I am the vice-president of the Foster Rhode Island Preservation Society. We received a grant to purchase the GPSmap 62sc in order to correctly locate the 148 Historic Cemeteries in the town as well as numerous ruins and historic sites.

I am now trying to get the g-raster program set up and am working with their support.

The Garmin Birds Eye maps are really not useful for our purpose as many of the sites we need to mark are located in heavily wooded areas and it is important to know where the wet areas are in order to avoid treking through swamps. These don't show up on ariel photos.

I didn't see any RI maps here that fit the bill and the RI DEM had nothing either so the Topos that I downloaded from the USGS store have to be it.

Thanks, The Foster Bear


If you are marking corners or other points be sure to use waypoint averaging. Multiple samples can get the point accuracy to within a few feet.


Quote from: The Foster Bear on January 03, 2012, 10:03:50 AMThe Garmin Birds Eye maps are really not useful for our purpose as many of the sites we need to mark are located in heavily wooded areas and it is important to know where the wet areas are in order to avoid treking through swamps. These don't show up on ariel photos.

I don't think you actually looked at the link I posted above, so here it is again:

These are not aerial photo's, the are scans of USGS 24k topo quads. They should show wetland areas. You can see an example here around the word "RIVER":

What kind of maps are you trying to create yourself? I think the Birdseye product is the same thing you're getting from USGS, and for $27 it really makes creating your own maps a fools errand. There is no practical size restriction to how much Birdseye imagery you can use.

The Foster Bear

I did in fact follow the link you posted earlier and under examples they show what appear to be overhead photos, not unlike what is in Google Earth, perhaps taken at different times but images none the less. Scrolling down the map list the Topos 1:24000 are listed at $129 each section.

I have downloaded g-raster and registered the copy. I then converted the USGS Topos that I had downloaded and was already using as overlays in Google Earth. The program worked like a charm and I now have the maps in Basecamp.

Many of our Historic Cemeteries were family lots on farms now long gone and were accessed on cart paths now long overgrown as well. Some were last documented nearly 100 years ago. Our task is to reestablish their locations and map them using GPS data so that they don't get "lost" again. Some of these may now be a mile into heavily wooded areas with considerable wet areas between the current roads and the ultimate location. So any wet areas obsured by trees or shrubs is a problem.

Some of the members assisting me are in their 80s so I really don't want to get into a swamp or marsh. I am the "kid" at 65, so I don't like to take chances.

Thank you again for your assistance...I will likely need more before I'm done.

The Foster Bear


Sorry, I don't know why that link won't work for you. The expensive topo maps are a completely different product. Birdseye topo costs $30 for unlimited downloads. Trust me, they are the same maps you are converting with g-raster, but all ready to use. This is what you should be seeing at that link

Rich has written about them at GPSTracklog:

the screenshots look like this, NOT like aerial photos. As I said above, you can see the wetland area clearly marked in this one


Don't get me wrong... I am all for making my own maps and have posted many of them here. In fact, I posted a number of custom maps made from USGS 24k topo's myself, such as this:

But that was right after Garmin introduced this form of map, and before Birdseye even existed. Now that Garmin offers the USGS 24k topo's as unlimited downloads for $30, frankly it makes no sense at all to roll your own. It is very time consuming to make your own maps, and $30 doesn't buy a whole lot of my time.  ;)

Aside from that, the Birdseye product is superior in many other ways. As stated more than once above, there is no limit to the size of the Birdseye maps. You can have several states worth if you want. Using the Custom maps (.kmz) format, after extensive trial and error I determined that the largest map I could make was about 20 miles x 20 miles before reaching the 100 tile limit.

And furthermore, Birdseye is more responsive on the gps, zooming and scrolling faster (in my experience at least). It is also visible over a wider range of zoom levels.

Indrid Cold

You need to realize that there are two BirdsEye products for the US, one as you have seen is satellite imagery and the second is USGS TOPO maps. Body has been trying to recommend the Second product not the first.

The Foster Bear

After checking back on the Garmin site I did find the Birds Eye Topo link and downloaded the 4 quadrants that cover Foster, RI. After deleting the maps I had generated with g-raster, I downloaded the Garmin maps and they are now on the unit.

I have to say that the g-raster program worked flawlessly and I was not unhappy with the resulting maps. The 4 quadrants after breaking them into bite sized pieces did exceed the 100 image limit. I copied them to my device using explorer which was the only way to get them on but then the device only showed 2 of the 4 quadrants.

Sooooooooo, thank you all for your patience walking me through this.

The Foster Bear


If you ever use G-Raster again for topo maps (or any other kind), you can get more maps on your unit with some simple adjustments:

- Loading a USGS topo map using the 1:24K topo map input type will automatically crop the collar of the map, which will let you get more maps on.

- You can also rescale the map to a slightly smaller size, which will result in fewer tiles with no major loss in image quality.

For example, using decollaring and a rescale factor of 1.7 on a USGS topo map, you'll be able to fit 6 quad maps under the 100-tile limit.


I think that's about right. Scaled at ~3 meters (10 feet) per pixel, a 24k quad is about 4000x4000 pixels. So that would break down into 16 tiles of 1~000x1000 and 6 x 16 = 96 tiles.

My own experience shows that if you try to reduce the resolution of the source image more than this, details like closely spaced elevation contours start turning into blobs.