[Talk-it-piemonte] Mappa Del Piemonte per GPS Garmin

[Kay F. Jahnke]

Dear group!

After several years of only small changes (apart from the rare updates 
of the OSM content in my map) I have created a new version with 
different contours. The original map was using the contour lines from 
the CTRN dataset. While these were a valuable asset and proved to be 
quite reliable, I was never entirely happy with them. This was due to 
the fact that - as far as I am aware - the DEM the CTRN was using was in 
parts derived from the CTR and interpolated where there wasn't enough 
detail. So, especially in more remote areas where the CTR only provided 
50m contours, the CTRN contours weren't really very good.

Some time ago, when browsing the data at dati.piemonte.it, I noticed 
that a new DEM had appeared there, which was based on a reasonably 
recent LIDAR survey of the entire piemontese territory. This DEM is very 
detailed (5m X 5m squares), and promised uniform quality over the whole 
area. If any of you are interested, the most accessible form of these 
data are the GeoTIFF files in this dataset:

RIPRESA AEREA ICE 2009-2011 - DTM

I had a good look at the data with QGIS, was happy with what I saw, and 
so I decided to make a set of contour lines for my map. Using the same 
basic method as I used to convert the CTRN data into garmin img files, I 
did this:

- downloaded all of the GeoTIFFs
- created a VRT file from them
- created contour lines with QGIS' contour plugin
- cut the shapefiles with the contours to the tiles my map uses
- converted the shapefiles to intermediate OSM format (with ogr2osm.py)
- converted the intermediate OSM format to garmin images with mkgmap
- built the gmapsupp.img with the new contour tiles

Next a friend of mine and I did some testing with the new contours, and 
all seemed well. So I figured that I might as well make them part of the 
official distribution of my map. I asked dati.piemonte.it for permission 
to use an abbreviated attribution on the GPS unit's splash screen, which 
I received. Now all was ready for the launch and the new map went online 
a couple of days ago!

As ever, there is a gmapsupp.img file for the GPS unit, and a version to 
use with basecamp. Instead of Qlandkartegt, which used a basecamp-style 
install, I now recommend Qmapshack, which can use a gmapsupp.img 
directly, so if you can live without basecamp, just download the 
gmapsupp.img. The maps can be found via

http://www.piemontegps.altervista.org/

Alternatively you can go straight to the download page at

http://rossanigo.com/mappa-piemonte-per-garmin-ezp-58.html

This is a bit confusing now, because it also offers the BDTRE-OSM map; 
my map is a bit lower down under the heading 'CTRN-OSM', where you can 
see the new 2017-02 versions.

I hope that the new contours make my map better - the new contours have 
one small drawback which is their larger size; they need a bit more 
memory and are a bit more detailed, so rendering times may be slightly 
longer. I think the better quality is worth it. I'd like to hear what 
you think!

With regards
Kay F. Jahnke