Catamaran Cruising

Well to start creating a chart from a digital photo, first get your photo . I am using a Samsung A70- most android phones will do. However I don't use the stock camera app It does not have the controls , it can be used but it causes complications . I installed an app called open camera.
It has a lot of controls particularly one you can set it to take  .PNG pictures rather than .jpg . The  .PNG format is very good for txt  , an iPhone uses .PNG for screen shots .
 You can scan a chart many scanners have an .PNG option if you have an iPhone it's best to take the picture of the chart then screenshot it and use the screenshot to make the chart. It is possible to convert s .jpg to a .PNG with a convert app..
Anyways, here is my photo of a chart of St Malo out of bloc marine .
By the way sorry the photo a small it might make the txt quite blurry

I was careful to line up the long and lat with the edges , it's easy to aline with a photo editor but mapcal2 does take account of slightly skewed charts and so does opencpn . You have to be careful to try to make the picture flat and the grids parallel, but it will still callibrate and produce an accurate position even allowing for lens distortion. The program is part of the seaclear navigation package that is freely available for Windows it is 10 /20 years old and will run on xp vista windows 7 .. it should run on win 8 and 10 but might have to run with s compatibility mode , it's available for free download here . Its best to down load and use the most recent version 
http://www.sping.com/seaclear/
The download is a library and you have to extract the programme. Mapcal2 out of the zip folder into a folder and put the chart photo PNG file in with it

I took the picture allowing a good border around the edges to minimise distortion which I then used a photo editor (gimp free download and it is very good) to crop the edges off . It can be used to improve contrast and  brightness.

Run mapcal2.exe and then open the .PNG.  In my case it was stmalo.png you will be faced with this 
Well nearly this .. I run Linux so have virtualbox and run vista in it   basically the box window has a running version of Windows in  and as mapcal2 only runs in window I run it in that . I can have vista ,XP, win7 even raspian pie all at the same time!

The box shown is the border box you can mark the corners of the area of the chart that you want to use as a raster image . The quilting option in opencpn let's you move from one chart to another seamlessly you can of course switch by choice. Between vector raster and bought charts even producing your own little charts of unsurveyed channels or bays. The north Cornwall coast has miles of unsurveyed bays .

It's just a case then off filling boxes in with latitude an longitude for selected points only 2 points are needed but you can use as many as you need and in particular if the photo has any photo grid distortion you can select points to straighten the distortion. Top left corner has a little drop in the latitude line . I will post a picture of how the calibration allows for this and produces accurate GPS grid.

The lock lat long allows you  to freeze lat long points
It is actually very easy and simple  to use in practice.

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