Charting, the game of 7 errors

A recent Thread on the Hisse Et Oh forum, I salute by the way, I challenged the accuracy of the chart data provided on the electronic charts. The subject concerns the observation that, in some location, existing information on the Navionics Marine HD application, or on some chartplotters, are missing on Navionics charts available on the website x-traverse.com used with iNavX (and MacENC). Quote :

"So the question is : Is there a difference between the 46XG map and the Europe map or is the difference due to the software that makes the cards tick?. ”

Damned ! It seemed useful to make comparisons closing electronic charts from various sources. As far as I know particularly well geographic location used in example, since it is the approach to the port of Concarneau, near the beacon tower Le Cochon, passage I borrowed hundreds of times over the years I was working with Glenans Nautical Centre.

On port in the channel (entrance) et à l’extérieur de celui-ci à environ 300 meters high, are Lué Vras rocks (or Vraz depending charts). Il va sans dire que les bateaux n’ont rien à faire là. But it is a fact that the heights of these drying rocks does not appear on some electronic charts.

Navionics versus Navionics

Navionics versus MapMedia (TimeZero)

Here we compare the vector charting with raster one. However, must logically find the same location at equivalent scale. Dans le cas ci-dessous, MapMedia chart is strictly reproduction of the raster chart from SHOM.

Actually, the overlay of the two charts is almost perfect, aligning markup location as a reference. On note cependant un léger décalage sur la droite,

Navionics contre CMap

Once aligned beacons, there is a slight shift of Lué Vras rocks eastward. Globalement, except depths, charting is faithful.

What can we conclude ?

Ce qui est rassurant, is that the charts topography, namely the geographical elements positioning, est respectée chez tous les éditeurs. Reproduction of official charts correctly georeferenced. Which is damaging, on the other hand, c’est le manque de précision dans la reproduction des informations. Red Card to CMap, Yellow Card to Navionics cartography delivered via X-Traverse. Concerning MaxSea MapMedia chart, it uses SHOM chart duplication and therefore has no merit.

About the above issue on the forum HEO, la réponse a été fournie à notre ami Jean Debèze (¹) by X-Traverse support :

« C’est clairement une limitation des cartes Navionics 46XG revendues par X-Traverse comparées aux cartes Navionics Silver incorporées dans les traceurs. I will ask Navionics to review this in their cartography department and see if additional data can eventually be put into this region of 46XG. Sorry I have no immediate solution, les données qui nous sont fournies sont celles que nous sommes en mesure d’offrir en téléchargement. ”

However, should minimize such a gap. La zone concernée est loin en dehors des chenaux de navigation, and if knowing the elevation of these rocks can be useful to evaluate a glance the level of the tide passing Le Cochon, cela ne crée pas de risque pour la navigation. Therefore let's be moderate in our comments about. Navionics is by far the most accurate charing and better updated around the World (²), and inaccuracies encountered by boaters can be reported, avec captures d’écran et photos à l’appui, until service dédié by Navionics.

I want to say to the readers that I have no particular interest in extolling the virtues of this charting, ce n’est que le constat effectué lors de navigations personnelles, ou encore rapporté par des sources fiables, in many areas of the Globe.

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(¹) Installing an iMux aboard "Lady Jane"
(²) Charting compared, a mixed result
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