NOAA Nautical Charts

                                Methods for conversion of NOAA nautical charts to TIFF images

        Overview - the basic process was to convert the BSB charts from
        MapTech into ArcInfo grids using the ChartViewer extension from
        NOAA and Spatial Analyst extension from ESRI in ArcView 3.2a.
        The grids were then reprojected to UTM, borders were clipped,
        and colors were matched before converting to TIFFS.  Three sets
        of TIFFs were made, the unclipped charts in UTM NAD83, the clipped
        charts in UTM NAD83, and the clipped charts in UTM NAD27 (for the
        Coast Guard).

        DETAILS

        Conversion - We got the newest BSB-format NOAA charts from MapTech,
        Edition 3.0, Region 2 (Block Island, RI to Canadian border).  I
        copied these to a local drive on the Dell server.  I then downloaded
        the BSB ChartViewer extension from NOAA's website:
        http://www.csc.noaa.gov/products/chartview/
        and installed in on the Dell server, which was running ArcView 3.2a.
        I also installed ESRI's Spatial Analyst 1.1. on this server.  Then,
        for each of the 58 charts in Maine waters, I added it to ArcView
        with the ChartViewer and saved it as a grid with Spatial Analyst.

        Projection - As I converted each chart, I checked to ensure they all
        had a consistent projection system.  This was for the most part true,
        all were in a Mercator projection.  However, the latitude of true scale
        varied between charts based on their location.  I recorded each chart's
        latitude of true scale, and then coded an AML to run through and define
        each chart's projection in its corresponding grid.  Then, I coded another
        AML to go through and reproject each grid to UTM with the following
        projection parameters:
        projection utm
        zone 19
        units meters
        datum nad83
        spheroid grs80
        For the record, the Mercator projection used with these charts was based
        on the NAD83/WGS84 datum.
        A second set of grids was created with the same UTM parameters above, except
        datum nad27, spheroid clarke1866.

        Clipping - Once I had a complete set of charts as UTM grids, I coded an
        AML to run through each grid, clip it to the boundaries of the chart,
        and convert any NODATA cells to values of 2 (white).  This operation was:
        grids_clip_83\g%quad% = con(isnull(selectpolygon(grids_utm\g%quad%, tempcov, /
        inside)), 2, selectpolygon(grids_utm\g%quad%, tempcov, inside))
        The boundaries of each chart were taken from an ArcInfo coverage, which was
        on-screen digitized using the charts themselves.  The coverage from the
        earlier charts was not used because it didn't line up.  Also, the dates of
        the charts were added to this coverage.  An export file (.e00) of this coverage
        is on the CD-ROM(s).

        Colormapping - I found that most charts had inconsistent color maps.  The result
        was that I had to go through each chart and create an individual color map.  I
        first recorded a consistent set of colors to be used in all charts, then checked
        each chart's grid in ArcMap to see what values related to the various features.
        The colors used are:
        Feature		Color		R	G	B	Comment
        Text		Black		0	0	0
        Open water	White		255	255	255
        Coastal water	Light Blue	215	225	235
        Mid-water	Lighter Blue	240	245	255	Not on all charts
        Land		Khaki		240	220	190
        Towns		Darkest Khaki	175	160	130	Only on Canadian charts
        Intertidal	Olive		200	200	175
        Navigational	Purple		175	105	235
        Green buoys	Forest Green	70	160	0
        Bathymetry	Aqua		0	205	255	On most charts, also Loran "W"
        Bathymetry	70% Gray	80	80	80	On few charts
        Shipping lanes	Pink		240	195	255	On small-scale charts
        Boundary water	30% Gray	180	180	180	International water boundary
        Canada charts	Medium Khaki	190	175	145	Only on Canadian charts
        Regulatory area Steel Blue	100	180	255	NWR's, parks, etc.
        Cleared areas	Pale Green	200	255	215	Casco Bay charts
        Loran "Y"	50% Gray	110	110	110	On small-scale charts
        Colormap files were created for each grid with the appropriate RGB values, then
        converted to TIFFs.  The .cmp files are on the CD-ROM(s).

        Conversion - All grids were then converted to TIFFs using the Arc GRIDIMAGE command,
        with the appropriate .cmp file, and compressed with packbits compression.  LZW was
        not used so that the images could be utilized in ArcView (which doesn't support LZW
        compression).

        CD-ROM - The TIFF images, along with supporting files, were written to CD-ROM by
        the GIS Unit.  Three sets were created - unclipped images in UTM NAD83, clipped
        images in UTM NAD83, and clipped images in UTM NAD27.
                              

                                To create a catalog of the converted TIFF images, I wrote an AML to loop through all the images, capture their extent using [SHOW MAPEXTENT], and write that to a text file.

The text file was converted to DBF in Excel, and imported into SDE as this catalog.