Charts II: NGA - 2700 Charts

[r.fairman]

NTM.
Here is a section of a NGA chart i corrected using gpx import to OpenCPN


The total number of changes needed to bring this chart up to date was 30 and took 30 mins to apply using GPX The bouy icons we captured from a cmap 93 chart and save as xpm.s in the usericon folder. Still having problems where old Nav obect have to be removed I have created a image from the chart color as a xpm icon to overlay old nav objects. Works well at some zoom levels but is obtrusive when you zoom out. Can scaleable waypoint icons be introduced The other problem is submarine cables where a line is needed on the chart,
I seem to have gone down a route i did not agree with. A certain happy seabird will be pleased
Now the big question
How can i accurately plot these waypoints on an image i extract from the kap file. I can read x y coodinates from my cursor position in my image editor can i do the same in OpenCPN or can I convert lat longs to x y
If i can do this I estimate it will take another 45 mins to update an image file and reconvert to kap
Perhaps all of this could be done in a NTM plugin

regards

Richard

[HappySeagull]

Richard,off the wingtip(off the cuff as you'd have it)
as an idea
Using a new layer in Adobe or the gimp etc,You could draw straight grid lines on the chart,using the chart's illustrated lat/long...place your corrections in yet another layer.When done,delete the homemade grid layer and then merge the correction layer to the chart image.Well,you'll know what I mean,if I've described it wrong...

[HappySeagull]

Originally Posted by wdkester

My graphics/picture editor (ACDSee) doesn't seem to be able to open large jpeg files. Can someone recommend a free program that can create a tinn and a lng file from jpeg?

irfanview can do it.Just don't zoom in or out incrementally unless you are prepared to wait...
Use CTRL+H instead to see full size...

To convert downsize or recolour,Irfanview does these in its batch dialogue quite well.

[r.fairman]

Notice to Mariners

Is there a zoom level in OpenCPN which displays a kap chart at 100% I can display the image from a kap chart in Photoshop at 100% I need to do the same in OpenCPN. I have a utility that will overlay the screen with a configurable grid to help with positioning the Nav Objects.

regards

Richard

[HappySeagull]

Interesting...,if you look lower right corner,O displays zoom "True"scale as 1.0,2.0,etc.
On the "proper"chart I am testing,(using kapview alongside)this agrees as 100% zoom....

BUT some homemade charts only display as 0.98 or otherwise-not 1.0,2.0,etc which is a can of worms to do with the header or what?

[wdkester]

Originally Posted by r.fairman

Install ImageMagick and use the convert command at the command prompt

convert NAME.jpg NAME.png

regards

Richard

Richard,
My ImageMagick has a gui and when given a 35MB jpeg file and after several minutes it gets an error something like "Windows won't let me open a bitmap x by y"

nconvert does work tho so I'm OK.

Thanks

[P_Dub]

Originally Posted by HappySeagull

Interesting...,if you look lower right corner,O displays zoom "True"scale as 1.0,2.0,etc.
On the "proper"chart I am testing,(using kapview alongside)this agrees as 100% zoom....

BUT some homemade charts only display as 0.98 or otherwise-not 1.0,2.0,etc which is a can of worms to do with the header or what?

One thing that should have been done was to have exact number scale such as 1:10000 or 1:20000; not 19850 or such. Could this be done in the near future?
Regards
P_Dub

[HappySeagull]

PDub, you might have something there!Let's try it...!that could be why,alright!
no,unfortunately does not give me a 1.0 scale per r.fairman post above

in the same vein,

(Nohal?) I note on the https://github.com/ngacharts/ngacharts/wiki/The-Plan
that the scale should be taken from the chart...but I guess it needs dividing by 2 if the images are reduced 50% to calibrate.

I am building a portable calibration kit using mc2bsbh.exe,tif2bsb.exe,MapCal_2.exe,the images and a batch script.It's very fast...but it's because images-I'm pre-converting to 16colour tiffs in my own favourite editor...(yes,MapCal will do tiffs if in open dialogue choose "all files")

[P_Dub]

[QUOTE=HappySeagull;742495]PDub, you might have something there!Let's try it...!that could be why,alright!
in the same vein,

I have been using various programs and various success as well for that. But I still believe that no matter the screen it should be that way. Only few commercial program have this exact scale, say 1:10 000 or such. Those that do not have that they generally have problem with the adjustment of vessel (or boat) size.
Bye
P_Dub

[r.fairman]

Thanks for that BUT

I have self calibrated NGA chart 1:25000 scale. Scale appears correctly in the kap header as 25000 But when i zoom to what looks like 100% compared to photoshop the true scale displays as 3900 I can work with this but does anyone have any answers as to what true scale is displaying Surely at 100% display True scale should display the scale of the chart

regards

Richard

[r.fairman]

I am refining the application of NTM's to the image file and trying to improve the precision
When i place a nav opject on the image file and recalibrate its coodinates on the chart read out as
36.823078
28.288911

The coordinates should be
36.823178
28.288975

How much of an error is this in distance terms Is it within normal GPS error range and what degree of precision is acceptable

regards

Richard

[r.fairman]

Ok found out the answer

The difference in position of my nav objects when plotted on an annotated image file, compared with that stated in the NTM and plotted using GPX import is 13 metres

Is this level of error acceptable

regards

Richard

[r.fairman]

I have just refined the method of applying NTM's to a calibrated image file The precision is now 2.5 meters

Richard

[Surveyor]

Are you using a lat/long to pixels formula? A speadsheet could be set up to give pixel coords for each item (or a batch) to be placed fairly easily.

If the chart origin (0,0) is the top-left corner of the sheet, which all I have seen are, you can input:

# of pixels from top edge to the top border
latitude of top border
# of pixels to bottom border
latitude of bottom border
# of pixels to the left border
longitude of left border
# of pixels to right border
longitude of right border
--SSheet
formula for pixels/dms ratio
output proportionate measure in pixel coordinate pairs

Moving the chart image origin to the bottom-left border corner would greatly simplify things by removing the need to enter sheet edge to border widths and would also result in always positive pixel coordinates:

latitude of bottom border
# of pixels to top border
latitude of top border
longitude of left border
# of pixels to right border
longitude of right border
--SSheet
formula for pixels/dms ratio
output proportionate measure in pixel coordinate pairs

This would also eliminate the need to scale the chart image to match the scale stated on the chart or whatever it is you are doing.

You could even take it a step further and send the batch pixel coords with a descriptor (symbol file name) to a csv file and import that to photoshop which would place the symbol file at each pixel coord. I have seen this done before but I do not know how it is done.

I use mapping software (Autodesk Land Desk Top) and my setup is basically what I describe above except that my coord pairs are lat/long/desc. I import a csv file containing all the coords, symbol images are imported at each coord based on the descriptor and scaled based on the symbol to map ratio automagically!

No matter how it is done, it is not easy.

[bdbcat]

Richard....

OCPN TrueScale is the "true scale" as displayed on the screen. The relation to chart posted scale and zoom factor depends on the pixel pitch of the display, and the pixel resolution used in scanning the chart. All are variables from chart to chart and system to system.

Try it out. Get a ruler, measure a vertical distance on the screen (Mercator charts, please), and do the calculations. Pretty close for my eye.

Dave