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Old 16-10-2009, 18:40   #193
bdbcat
Marine Service Provider
 
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Join Date: Mar 2008
Posts: 6,160
CM93 at Darwin

Gone Troppo / ColdFusion....

There are several things going on here:

1. Failure to show anchors/chains and berth numbers is a bug. These are not S57/S52 standard objects, but are cm93 private objects. I will track them down, and get them rendered...

2. Failure to zoom further is not a bug, it is by-design behavior. Long time forum members will recognize my hot-button.

At this geo point, there is no larger scale chart in cm93 than the 1:20000 F scale chart. As you can see in the lower right corner box of the status bar, the chart may be zoomed to a factor of 4X overzoom. 4X overzoom is all that is allowed by opencpn. For a 1:20000 F scale cell, this equates to an actual onscreen scale of 1:4800, as indicated by the TrueScale value. Zooming further provides no more information, and exaggerates, (or overstates by implication) the inherent accuracy of the chart.

Theoretically, if we were to be compliant with S52 standards for big ship ECDIS displays, we should zoom no further than 2X.

I'll try to put it another way. Looking at the CMAP ECS coverage of the same area at 1:1500 on an F scale chart is nearly the same as looking at the 1:20000 paper chart of the same area with a 13 power magnifying glass. The only difference is that the features on a vector ENC are always rendered cleanly, without the pixellation that would result from looking thru a glass, or zooming a raster chart. Thus the misrepresentation.

I'd recommend you read Calder on this subject. He certainly writes better than me.

Frankly, the users coming from CMapECS and MaxSea have worn me down on this issue. My soapbox is getting thin. I'll say it one more time, and then throw in the towel.

Excessive overzoom on vector charts is a dangerous use of ECS, and will lead to misinterpretation of chart data.

The next version of opencpn will have an "expert" mode option, allowing near infinite overzoom. I will not use it.


Good Luck, and safe sailing
Dave
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