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Graticules and NOAA charts

May 21, 2014, 20:29
Post: #1
Graticules and NOAA charts
I'm looking at GIMP, and I'm wondering if I'm trying to use a 15 yard Kenworth dump truck where all I need is a pickup.

I’m working on NOAA nautical charts. NOAA recently released all of their free navigation charts as PDFs, which is a giant step forward for sailors.

What I need to do is crop the charts (they're huge, for the cockpit of a racing sloop) to 13x19, then add back in the border. This project is for printing hard copies on a large format (13x19 inch) printer.

The border contains the graticule, the scale of degrees, minutes and seconds.

The latitude is significantly different from the longitude, the size is quite different.

I see that GIMP has a grid that has the ability to configure the X axis independantly of the Y axis, but I’m having trouble wrapping my brain around the problem. I’m not an artist, by any stretch of the imagination.

I need to line the grid up with two points on the edge of the cropped PDF, one on the top or bottom, and one on the side, so that the grid reflects degrees, minutes and seconds correctly. (The PDF has a printed grid every two minutes.)

I need sixty seconds in every minute. (None of the charts cover a full degree. Thank god.) I think I can put independant labels on each minute.

But I don’t even know where to start my research on how to make GIMP do this.

Thank you!

~Jammer
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May 21, 2014, 22:03
Post: #2
RE: Graticules and NOAA charts
Thank you!

I'll work now on figuring out how to take a screen shot. I'm pretty sure I can make a suitable screen shot (or two) that shows my problem.
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May 21, 2014, 23:12
Post: #3
RE: Graticules and NOAA charts
Okay, I have a couple shots I think will work.

GIMP opens the chart happily. I figured the PDF issue out. This is the lower right corner. I've included it to demonstrate two things: one, the size of the minutes of latitude are considerably different from the size of the minutes of longitude, and two, the numbers run "backwards". That is, because I'm in Puget Sound, latitude runs from south to north, and longitude runs from east to west.


.tiff  Lower Right.tiff (Size: 966.47 KB / Downloads: 32)

The next shot is a shot of the most important bit: how I need to divide minutes, both of longitude and latitude.


.tiff  Seconds.tiff (Size: 238.97 KB / Downloads: 31)

The last shot is of a cropped chart, and it's an example. I just cropped it for this reply, it's not the chart I want to make. I take the original chart, crop it in some way to make if fit on my paper so that the part of the chart I want is there, and then I want to align the graticule back up to the printed lines on the paper. There are lines on this chart, and those lines represent, in most cases, two minutes of longitude or latitude, and I need to be able to line a suitable graticule up to them as precisely as possible, and then print the whole mess out.

(Sometimes, to make the exercise harder, NOAA leaves different minute lines out, and there's only lines every three minutes, or five minutes, depending on the chart and the area, and what's in the area. They do it to avoid "chart clutter", and to make sure I break out in hives when I'm trying to figure graticules out.)


.tiff  Cropped Chart.tiff (Size: 220.61 KB / Downloads: 34)

Thank you for your help!
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May 22, 2014, 00:08
Post: #4
RE: Graticules and NOAA charts
No, I don't want anymore lines on the chart.

I assumed that the grid would be the easiest way to get the marks on the border.

The Guillotine may be exactly what I want, assuming it works in both vertical and horizontal.
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May 27, 2014, 03:39
Post: #5
RE: Graticules and NOAA charts
Thank you!

I can't figure out how to make this forum let me write your name... that's how good *I* am with computers.

I'll be looking at your script in detail.

So is GIMP for experts who can write scripts? Should I be studying how to write scripts?

Here's another piece of my puzzle: the Coast Guard puts out updates to these charts every Wednesday. So when I wake up each Thursday, my precious charts are out of date.

In the days of paper, one raced to one's desk every Thursday morning, looked over the list of updates, and started making updates on the chart with one's drafting equipment.

Now, it would be good to use GIMP on the PDFs, while replacing the chart on the bottom of the stack of overlays occasionally.

So I've been looking over various Mac programs that allow me to do that, including iDraw and OpenOffice, and while OpenOffice seems to have knocked itself out of the running, iDraw lets me draw a graticule fairly quickly. But replacing the chart on the bottom could be a pain in iDraw.

So is the idea behind GIMP that I can customize it with scripts, instead of using it out of the box?

If so, I can see how, after a long, painful process of developing appropriate scripts, that it could be much easier to use GIMP to update charts rather than iDraw, in spite of the fact that superficially, iDraw appears easier to use.
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