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Old 21-11-2015, 12:34   #1
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Determining Scale for MapCal of Scaned Sea Temp Chart

I am going to Rutgurs Sea Surface Temperatures page

Sea Surface Temperature - IMCS Coastal Ocean Observation Lab

I click printable copy of the chart, save it as a pdf, convert to png then convert to bmp. I open it in MapCal convert it to WIC and calibrate it.

When I put the gird on it doesn't match the chart, I get waves in the grid lines, after activating the changes hovering the cursor over the corner points the lat is somewhat close the lon is of by a few to several minute.

The only thing I don't know about the Sea Temp Chart is the scale. So I go with the defalt.

Is this the problem? When the scaned chart has no scale how is it determined.

Thanks in advance.
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Old 22-11-2015, 10:21   #2
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Re: Determining Scale for MapCal of Scaned Sea Temp Chart

Quote:
When I put the gird on it doesn't match the chart, I get waves in the grid lines, after activating the changes
This usually means you don't have the calibration points' lat/lon correct.

AND/OR you are calibrating as the wrong projection- I mean, you must know if the image is MERCATOR, Transverse Mercator, Universal Transverse Mercator and so on.

AND/OR the image you are calibrating is NOT an accurate projection at all and is not intended for navigation. .. for instance, a gas station road map is about showing roads plainly...likewise a Rutgers Sea Surface Temperature map is about showing temperatures, not for gps navigation.

That said, Your "best bet" for most maps is MERCATOR, unless you are closer to the poles.
(The image can sometimes be correctly resized to approximate a correct projection per its latitude)

As to "Scale", without doing some math here, try a simple way that might take a few tries... view your map image at a scale where it is still plain and not a bunch of useless pixels on your screen Compare to a similar chart covering the same view in Opencpn and note the scale Opencpn displays in the lower right. This is a good starting point ..just a wild guess but it'll likely be something like 2500000 or at least 1000000 unless they are so kind as to offer very large and plain pdfs for free
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Old 22-11-2015, 18:44   #3
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Re: Determining Scale for MapCal of Scaned Sea Temp Chart

Thanks for the reply,

I use the Mecator projection and I check my lat and lon coordinates a couple times. It seems to me it is the scale. To take a stab at scale I use my caliper to measure the distance of 1 degree of lat. I got 1.6 something inches I divided that by 60nm and got 1- 22,000 plus. It still didn't work out. I probably need to talk to someone at Rutgers.
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Old 22-11-2015, 20:52   #4
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Re: Determining Scale for MapCal of Scaned Sea Temp Chart

I opened it with the weatherfax plugin. I chose mercator as input projection. It looks OK to me.

See the results in the attachment. (Remove .doc)

JM
Attached Files
File Type: doc SST.kap.doc (130.3 KB, 17 views)
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Old 22-11-2015, 22:09   #5
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Re: Determining Scale for MapCal of Scaned Sea Temp Chart

there are 60x6076x12 inches in every degree of latitude. But you "see" it as 1.6 inches, therefore (60x6076x12)/1.6
so 1 inch on your chart represents 2,734,200 inches.....
say, 1/2700000

1/22000 is a suitable scale for a harbour plan.

6076 is as I recall a nautical mile but you can look it up on wikipedia,no doubt.
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Old 23-11-2015, 08:27   #6
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Re: Determining Scale for MapCal of Scaned Sea Temp Chart

Houjelm thanks for the tip I have looked up plugins in the manual found weatherfax. I will try it out. Thanks

HappySeagull I relooked at my math I made a mistake on my unites when doing the math, thanks for the correction.
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Old 23-11-2015, 09:31   #7
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Re: Determining Scale for MapCal of Scaned Sea Temp Chart

Houlejm I tried opening you file in Word since the icon shows, but I just got text, and I wasn't able to open it in Google Earth. I have just started with OpenCPN and have no charts in it yet. I am guessing I must open it with CPN and have the appropriate chart in a CPN directory.

I have been using SeaClear.
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Old 23-11-2015, 09:55   #8
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Re: Determining Scale for MapCal of Scaned Sea Temp Chart

Chessyman
Your have to delete .doc from the .kap filename as it's added to get round file size limits here on the forum.

Sent from my XT1068 using Cruisers Sailing Forum mobile app
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Old 23-11-2015, 09:57   #9
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Re: Determining Scale for MapCal of Scaned Sea Temp Chart

I heartily recommend you get on to OpenCPN 4.0. .. SeaClear is ...ok but the WCI files are a nuisance that I'm glad I never got much into... because nothing else can see them?
But keep it around! - I still find its MapCal2 handy for calibration of large charts.
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Old 23-11-2015, 10:50   #10
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Re: Determining Scale for MapCal of Scaned Sea Temp Chart

Quote:
Originally Posted by Chessyman View Post
Houlejm I tried opening you file in Word since the icon shows, but I just got text, and I wasn't able to open it in Google Earth. I have just started with OpenCPN and have no charts in it yet. I am guessing I must open it with CPN and have the appropriate chart in a CPN directory.

I have been using SeaClear.
You must delete the .doc

It is now a KAP file and can be seen with OpenCPN. I made it with the weatherfax plugin in OpenCPN using your source.

Here is the recipe:

- Get the image from the source into your browser
- Right click in the image, save image as... It will be a .jpg image
- Open it with weatherfax plug-in in opencpn
- Calibrate it.
- When finished, it will overlay your charts in opencpn.
- You can then export it as a .KAP file for use in any charting program.

JM
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Old 25-11-2015, 19:40   #11
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Re: Determining Scale for MapCal of Scaned Sea Temp Chart

Great, thanks, I will work on it. I have just started on OpenCPN. It seemed like a more feature rich program. However I have liked SeaClear, but now want to switch to OpenCPN.

Thanks for the help.
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