Index

Charts are pictures. Maritime charts contain images of water, land, structures, depths, navigations aids, and many other things needed for safe navigation. These charts are created in two very different ways just like computer pictures; raster and vector. The decision of which chart program to use is influenced by the type(s) available in your area of interest and how you like to work with them.

Raster images are used in a lot of print media. They are composed of small dots that when viewed at arm’s length appear to be solid lines and colors. Look at a newspaper photo with a magnifying glass and you can see these dots. An electronic display puts images on the screen in exactly the same way and the dots are called pixels; picture elements. If you zoom in on a raster computer image far enough you will see the pixels as a bunch of colored squares. This raster image is stored in a sequential list of pixels along with their color. Exactly how they are processed and stored is determined by the picture format, i.e. file extension. Some familiar picture types are .TIF, .PNG, .GIF, and .JPG. Some chart formats are .RNC and .BSB.

The photographs on this web site are raster images and it takes only a few minutes to optimize, spruce up, cut to size, and place them on the page using top end raster software like Adobe Photoshop. Most computers come with a basic program to view, edit, and convert one file type to another that can be used. There are far fewer programs available that accept chart file formats.

Vector pictures might look similar but are created and stored quite differently. They are composed using a pallet of primary constructs such as straight or curved lines, circles, or polygons. These are then stretch, rotated, and distorted into their final shape and stored as their basic type, where it starts on the screen, its direction, how it is modified, where it stops, and its color. Data stored like this has the potential to be a much smaller file than its raster counterpart but this is not the primary reason vector images are growing in popularity and used for creating charts.

Because the computer redraws the image every time from a set of instructions, size is not a consideration in the design. In fact when I am creating a vector image I usually start with some random scale. If you want to see or modify some small detail just ask the computer to redraw that portion with everything bigger. The detail appears crystal clear. When finished I size and convert to a raster image that web software accepts. Some vector file types are .Al, .SVG, and .DWG for pictures and .000, .S64, and .ENC for charts. Yes; unlike their raster cousins most do not recognize these file extensions.

 

You might ask then why these vector drawings are not used more often.

Imagine drawing the thousands of basic elements and linking them seamlessly together to make a photo quality picture of your aunt Sadie. Believe me this is a challenging and time consuming process with a long learning curve to gain proficiency. Computer programs to convert raster to vector format have come a long way but the results are still not very good and require a great deal of cleanup. These complex images make a huge file and unlike charts or maps you probably don’t have any desire to zoom in for details of your dear aunt.

Vector charts are drawn by combining several basic shapes into icons, like a buoy or a light. This same icon can then be inserted any number of times. The expression goes; saved once, used many; very efficient.

To make vector charts more interactive and meaningful a database is usually created for each map icon. By clicking on it the information is displayed. For a navigation aid it might contain: name, number, light color, height, latitude and longitude, and the last time the battery was changed. The chart is not cluttered with data for which the viewer has no interest. Also you can do things like display only filtered information or shade water depths to highlight hazards based on your vessels draft. This is not possible with raster charts since the file only knows about one pixel at a time and has no idea what physical item it is use to represent.

On this web site the logos and a few other elements are created in vector format using programs like Adobe Illustrator so they can be scaled up or down with no loss of quality. The vector image of the LSPS burgee on the main page above our mission statement is exactly the same one used as the marker for dot points in many locations throughout the site. I can just as easily take this image and use it on a billboard. It would still look perfect.

Generally NOAA has ocean, coastal, and ICW charts in both formats. Inland charts for rivers and lakes are the responsibility of the Corp of Engineers and some are only available in raster format. The conversion to vector is slowly proceeding for the cash strapped agency.

Most chart viewing programs, especially the free ones, are either raster or vector. Full navigation programs use only raster or both formats. So if most of your boating is on inland waterways you might choose a free or inexpensive program that only loads raster charts. If you want coastal, open water, or ICW areas, the more serious programs that can use both chart types might be for you. I will go into more detail on finding and downloading charts including their web addresses in later chapters.

Some of the raster programs allow you to create and use your own charts. You can do this by taking a picture or scanning for instance a placemat and then annotating it with any raster drawing program. Load this into your chart program and register it with two points of known latitude and longitude. Snap a series of waypoints to create a route which you can load into your GPS for a hike in the forest or sailing on a local lake for which no chart is available. More on this in the next chapter.

I made one for St. Joe bay in Florida using a copy of the NOAA chart then snapped waypoints for known or potential scallop rich areas along with deep water routes between them. When loaded into my Garmin Map76 GPS we had no problem finding any of them miles from any observable navigation aid. Unfortunately the scallops must have used a different set of waypoints. For this project I used one of the three programs discussed in detail later. Clue: It’s the free one.