Splitting mpw files

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Feb 13, 2011, 11:06:09 AM2/13/11
to Mapwel Forum
I have been loading a large area of data into one mpw file, to ensure
consistency across maps.
The only way I can find to clip these files into an area that contains
the maximum number of points for a Garmin img file is to use Image -
Clip. This is a tedious and inexact process, and I have no way of
knowing just how large I can make the area.

Is there a better way, or would it be possible to add the capability
to clip the map file automatically? I think that it would still be
necessary to edit each map file before export to Garmin, to make sure
the maps had unique numbers.


Feb 14, 2011, 4:45:03 AM2/14/11
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Creating very large map at once is not recommended. The maps for GPS
are supposed to be created by tiles (separate img files) that are
later merged into large GMAPSUPP.IMG file. There are multiple factors
affecting the max. size of single tile (img file), mostly imposed by
file format - cities number, binary file size, etc. While overall
GMAPSUPP file can have virtually any size, the child img files are
limited to about 16-20 megabytes each (max 16 MB binary file + text
labels and other sections). Area of the map is not very important in
map splitting to tiles, but large maps (larger than 22.5 Lat/Lon
degree) are coded with lower coordinate accuracy by Mapwel.
Current version of Mapwel does not have tool to calculate if map in
the work area will fit into single img file, but I will consider
adding such tool.
In general, I would recommend to create tiles only up to 100x100 km
large. To ensure map consistency between the tiles (especially in case
of routing maps), I do recommend the following: 1. place (any) POIs to
all border nodes, use snap to nodes option to ensure precise position.
2. Save copy of the map with these POIs, erase all other objects and
leave only 'border' POIs there. 3. Merge the 'border' POIs file to
next tile map and use these POIs to place border nodes in this tile
precisely. 4. Delete POIs. This approach helps to achieve consistency
between the map tiles.

I plan to add more sophisticated tools for map clipping and border
nodes alignment in a near future. Above guide is a work-around for the
current version.

Best Regards

Mapwel team


Feb 14, 2011, 2:41:05 PM2/14/11
to Mapwel Forum
Large maps may not be recommended, but it is the only way I can create
maps with consistent information and display parameters across 7.7
million square kilometers of Australia.
I have boken it up into the 7 states and territories, at an average of
1.1 million sq. km each. Will try the suggestion of creating border

Note also that it is quite frustrating to split osm files, and then
merge them again in a mpw file. I understand you have a range of
reasons for limiting the size, but shapefiles can be imported over a
larger area. Could the limit be raised?


Findlay MacDermid

May 21, 2014, 1:19:24 PM5/21/14
to mapwel...@googlegroups.com
Could you elaborate please ""There are multiple factors affecting the max. size of single tile (img file), mostly imposed by file format - cities number, binary file size, etc"

I am having several problems. My applicaition is attempting to load a very dense shapefile into garmis. the file consists of a very dense point grid (spacing about 60mx240m) with about 8000 features. When I load it into the garmin it behaves oddly in the field. station numbers are often not what I specified or do not show up at all. My gut feeling is that, like most garmin problems, the root of the issue is the garmin file structure. it would be helpful if I know what the max number of features for a given symbol type is. I use "small city" because I like the way it looks on the garmin display. The area is not  large (Maybe 30 km x 30 km) but it has a lot of points within the area making me think I am running into the same type of issues that one might have with a larger map.

Do I need to split the dataset up to get it to load properly? I assume I would then make multiple .img files and batch load them with the other vector data? What is the max number of points for an .img file?

I'm having another problem whereby some of the symbols are displayed differently (incorrectly) on a garmin 60CX compared to my 78. Any thoughts on that?
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