Adding Navigation Charts to Maps in Saga: KAP, BSB, S-57
Abstract: After a
survey of "free" international sources of navigation charts (which
yields only a few States that do so), the exercise goes on to show how
to add vector format charts (an enhanced type of shapefile assembly) and
raster format charts (a special format developed commercially but now
used universally) to maps in Saga. Individual scientists will
probably need to purchase local navigation charts, for most locations,
due to the small number of States that provide them freely.
Preliminary Reading (in
OceanTeacher, unless otherwise indicated):
Charts (ENCs) - Vector files of navigation charts; composed of
shapefiles and annotations
Charts (RNCs) - Raster scans of navigation charts
Google List of Online Free Nautical Charts
- Some free charts, but mainly for sale by agents. See the MDL
Survey below for more information.
- 11485.zip (raster RNC) -
Chart for area along the east coast of Florida, USA (see source
- US5FL83M.zip (vector ENC)
- Chart for area along the east coast of Florida, USA (see
source info below)
- Nautical Chart Reprojector - Utility program provided by
NOAA for reprojecting BSB/KAPS files to orthogonal WGS84
World Borders Dataset, by Bjorn Sandvik (use
Brown and Pablo Guilherme
This exercise is provided only for instruction in how to work with these
digital files, and it is not to be a considered as training, instruction or
advice in navigation. Do not rely on the materials here for any maritime
purpose, other than study, because they are assuredly out of date and are selected only as
examples, and not for any actual use.
- 1. The survey of "free"
digital nautical chart sites is presented below in the last panel. You
can immediately see that the great majority of States do not provide
anything free at all. Most of them refer you to commercial vendors.
The author has double-checked the Google list and provided further
information for States that do provide something. We salute the
following entities for their generous attitude toward earth data:
- NEW ZEALAND
- UNITED STATES OF AMERICA
- EAST ASIA HYDROGRAPHIC COMMISSION.
|2. Download and install the
Nautical Chart Reprojector program.
|3. Run Saga and load the
WORLD BORDERS to use for general orientation.
|4. Download the example chart
files to the folder DATA > OCEAN > BASEMAP > CHARTS and unzip them in place.
Examine the results and you find these new folders:
- BSB_ROOT - Contains the raster image files
- ENC_ROOT - Contains the vector shape files
|3. Here's the contents of the
- *.BSB - Text file containing the "recipe" for the combined
KAP files that follow
- *.KAP - Individual charts
- *.TXT - Publisher's notification to users about rights and
|4. The KAP files must be
reprojected first. so run the NOAA CHART REPROJECTOR.
NOTE: This is
a very effective program, but the user interface is extremely awkward.
Just be patient and work slowly.
5. Click on INPUT FILE > BROWSE and this interface
opens. Work very slowly through the DIRECTORIES on the left to find
the 11485 folder where the KAP files are located. Select the first
one, and click OK.
NOTE: If you have trouble finding the right location, just look at the
above sequence of folders:
USERS > [NAME] > DOCUMENTS > PROJECTS
Try to follow this same sequence. Just take your time, and it WILL
work. There are some dead-end routes that will cause trouble, but just
|6. Now click on OUTPUT FILE >
|7. Navigate to the same
folder as for input, and insert an appropriate filename, with the extension
TIF. Then click OK.
|8. Now you're back to the
- Check the INPUT FILE to see that it's got the right name and
- Check the OUTPUT FILE to see that it's got the right name and
- Set UNITS = DEGREES OF ARC
- Set FILE FORMAT = TIFF
- Set PROJECTION = GEOGRAPHIC
- Set DATUM = WGS_84
Then click RUN
|9. When the program is
finished, check the OUTPUT location to see that you have new *.TIF and *.TFW
|10. Select SAGA > TOOLS >
IMPORT/EXPORT-GDAL/OGR > GDAL: IMPORT RASTER
- FILES = New TIF file you just made
- INTERPOLATION = Nearest Neighbor
Then click OK.
|11. Look for the new raster
in the grids section of the DATA panel.
|12. Use ADD TO MAP to place the new
raster on the WORLD BORDERS map.
|13. Here you can see the
small dark area of the new grid, along the east coast of Florida (or
wherever your selection is).
|14. Enlarge it a bit.
|15. And here it has been
greatly zoomed to see how it fits. You can immediately see that the
WORLD BORDERS coastline is very crude and does not match up very well.
This is expected.
|16. On your own, you can play
with the color scheme. The raster is a classified grid, with few
colors (probably <20).
NOTE: One author (Guilherme) has experimented
with the Saga module VECTORIZING GRID CLASSES to "extract" separate
classified zones to polygon shapes from these rasters. For example,
you could create an entirely separate polygon shape for the light brown
areas here (probably wetlands). The possibilities are endless.
|17. Look back to Panel 5, and
you'll see that there were 5 other KAP files to work with. Here
they've been mapped separately (using the same steps as above). You
can see that they are subset maps or ancillary maps. The BSB file is
probably the "recipe" for how these maps combine when you have a real
electronic chart display system.
|18. Take the time to save the
grids (at least the first one) in Saga grid format, with appropriate names
|19. That completes this very
short introduction to raster chart usage. Now we'll look at the vector
|20. Here's the contents of
the ENC folder.
- US5FL83M - Folder containing shapes and text notifications
for the map
- CATALOG.031 - Text formulary specifying how the shapes and
texts fit together to make a map
- README.TXT - Information about the map's reliability
- USERAGREEMENT.TXT - Self explanatory
|21. Look in the US5FL83M
folder to find these files:
- US5FL83M.000 - Primary vector file, in S-57 format, with most
of the map objects; contains shapes
- US5FL83M.nnn - Ancillary shapes; also S-57 format; most are
- USnnnnnn.TXT - First (of many, not shown) text note to place
on the chart
Remember that the file CATALOG.031 specifies how the pieces fit together.
If you have a real electronic chart display system, everything will be
integrated accordingly. With Saga we can only use the pieces
separately, and admire the technology involved.
|22. Select SAGA > TOOLS >
IMPORT/EXPORT-GDAL/OGR > OGR: IMPORT VECTOR DATA
- FILES = First (and primary) S-57 file
Then click OK.
|23. These LINE, POINT and
POLYGON shapes appear in Saga.
|24. Here is the line shape.
It's also the east coast of Florida.
|25. Here is a zoomed section
of the northern end. The WORLD BORDERS shape is included just to
orient you. They don't match because WORLD BORDERS is very crude,
compared to the ultra-fine precision of a good navigation chart.
|26. Here we've selected the
line shape and selected ATTRIBUTES > SHOW to see the DBF table for it.
Clearly you'll have to do a lot of research to find out the meaning of the
fields. None of them is a clean list of feature names, so labeling
won't be easy.
|27. But you can use the
fields (after your own research) to work with the coloring. The yellow
polygon is from the World Borders, providing a classic example of how badly
low-resolution data would serve us for coastal zone purposes.
|28. Here is the point shape,
with one of the fields used for labeling.
Much work would be needed to convert these codes to understandable
|29. And here is the polygon
shape, colored by one of the fields. These are roughly similar to what
you'd get if you vectorized the grid classes from the KAP maps, as mentioned
in Panel 16.
NOTE: The broad band of blue represents the legal
"territorial sea" of the USA. This is a very old concept, predating
Law of the Sea zones which go much farther out.
|30. Just having the files and
knowing, now, how to get them into GIS, is only half the problem. It's
up to you to do the research to find out what these codes in the ATTRIBUTES
table mean. Remember, you don't have an electronic chart display
system, so you're peeking into a different world and trying to capture
useful information for other purposes, so expect a lot of work.
|31. Take the time to save the
new shapes to the folder PRODUCTS > SAGA > VECTORS > CHARTS with name like
|32. The above methods cover
only the mechanics of getting these valuable (but often neglected) map
objects into your GIS. The research needed to understand the different
features is all up to you. You can't use a map like the one in Panel
28, because nobody knows what a #39 means, so get ready for some extra work.
|33. MDL Survey of Free Digital
Navigation Chart Availabilities.
Based on the Google List cited above. Presumably all countries'
charts can be found either at the websites listed in the Google List or
through the IC-ENC website. The MDL survey below is intended to
highlight truly "free" digital charts, such as they are. Due to the
many URLs at each country, you must go through the Google List to research
the contents on the MDL survey. The few links below are to special pages within
the cluster of citations for each country in the Google List.
Countries with no information do not provide free digital charts of any kind, don't
provide clear guidance on what's really available or how to get it, don't
have enough English language information to make any determination, or only
provide chart visualizations of unknown projections (i.e. not WGS84).
Several States do provide dynamic websites where you can view (but not
download) maps; these online maps are not described here.
||Notes on Resources
||RAR files mislabeled as ZIP. Change extension
then unzip with 7zip or WinZip. Contents are BSB + KAP
rasters; can be read with Saga's GDAL grid input module
|Australia, Belgium - Nothing free found; please
notify the author if wrong.
||ZIP files containing BSB + KAP rasters; can be read
with Saga's GDAL grid input module
|Canada, Chile, China, Columbia, Croatia, Denmark, Ecuador, Egypt, Estonia, Finland,
France, Germany, Iceland, India, Italy, Japan, Rep. Korea, Latvia, Lithuania, Mexico
- Nothing free found; please notify the author if wrong.
||All available WGS84 charts (2) available as PDF
||The reference to WGS84 is the very
civilized way the Montenegrins inform us that the maps are not
projected and can be georeferenced, i.e. in Saga. They are
applauded for this information. Use the method in
2.14 Image Georeferencing in Saga.
|Netherlands - Nothing free found; please notify
the author if wrong.
||Annual compilation of all raster digital charts available free (180
MB); also the free sample here
||A sample raster file
New Zealand BSB Test Dataset;
||All rasters are BSB/KAP format, so
can be loaded into Saga with the GDAL import module
|Norway, Panama, Peru, Poland, Portugal, Russia, Singapore, Slovenia, Spain, Sweden, Turkey, United Kingdom
- Nothing free found; please notify the author if wrong.
||Online catalog interfaces to all vector (S-57
format) and raster (BSB/KAP formats) charts
- ENC charts unzip to yield S-57 format file, which can
be read with Saga's OGR vector input module (to yield point shapes,
line shapes and polygons), plus TXT notes to annotate the charts.
Main file to load has extension 000
- RNC charts unzip to yield BSB/KAP format, so can be
into Saga with the GDAL import module.
|Uruguay, Venezuela - Nothing free found; please
notify the author if wrong.
||South China Sea charts (vector ENC)
download the SCS ENC, user has to register with the EAHC.
Not checked by MDL.