Generate HTML-Map from image

Is there a way of automatically generating a HTML-Map compatible list of coordinates of polygon-like objects (e.g. countries on a map) with very distinctive borders?

Example image:

Map of CEE countries http://www.bankaustria.at/landkarten/CEE_2007_w524.jpg

Final output:

<map id ="ceemap" name="ceemap">
    <area shape="poly" coords="149,303,162,301,162,298,171,293,180,299,169,309,159,306,148,306,149,303" href="austria.html" target ="_blank" alt="Austria" />       
    <!-- ... -->
</map>

Any tools/scripts extracting the coordinates of a polygon-like selection would be helpful.

Answers


Open the map in Inkscape. If it is a bitmap, use Path -> Trace Bitmap to trace the edges. Clean up the vector data to include only the paths that you want to appear in your imagemap. Save the document, I suggest to a POVRay file. Now you have a list of vertices (and plenty of markup or metadata that you don't care about) in a plain text format. Converting from that to the requisite HTML syntax is still a problem, but not nearly as complex as the first step.

For what it is worth, there is a long standing feature request for Inkscape to include an option to export HTML image maps.


Thanks for your help!

Although Jonathans hint to use the Sobel filter definitely would work, I chose Sparrs approach of first converting the bitmap into a vector image (via Inkscape) and then processing the SVG file. After studying some of the basics of the SVG spec, it was pretty easy to extract the - for HTML image maps needed - X/Y coordinates from all the other junk and generate a suitable code.

Although it’s no rocket science, someone might find this piece of code useful:

// input format: M 166,362.27539 C 163.525,360.86029 161.3875,359.43192 161.25,359.10124 C ...
private static void Svg2map(string svg_input)
{
    StringBuilder stringToFile = new StringBuilder();

    // get rid of some spaces and characters
    var workingString = svg_input.Replace("z", "").Replace(" M ", "M").Replace(" C ", "C");
    // split into seperate polygons
    var polygons = workingString.Split('M');
    foreach (var polygon in polygons)
    {
        if (!polygon.Equals(String.Empty))
        {
            // each polygon is a clickable area
            stringToFile.Append("<area shape=\"poly\" coords=\"");
            // split into point information
            var positionInformation = polygon.Split('C');
            foreach (var position in positionInformation)
            {
                var noise = position.Trim().Split(' ');
                // only the first x/y-coordinates after C are relevant
                var point = noise[0].Split(',');
                foreach (var value in point)
                {
                    var valueParts = value.Split('.');
                    // remove part after comma - we don't need this accurancy in HTML
                    stringToFile.Append(valueParts[0]);
                    // comma for seperation - don't worry, we'll clean the last ones within an area out later
                    stringToFile.Append(",");
                }
            }
            stringToFile.AppendLine("\" href=\"targetpage.html\" alt=\"Description\" />");
        }
    }
    // clean obsolete commas - not pretty nor efficient
    stringToFile = stringToFile.Replace(",\"", "\"");

    var fs = new StreamWriter(new FileStream("output.txt", FileMode.Create));
    fs.Write(stringToFile.ToString());
    fs.Close();
}

I can give you one step of the process: you are going to need to use the Sobel filter (often called edge detection in programs like Photoshop).

After that you will need to find a tracing library in your language of choice.


I made some changes and implementation to the code of Gerhard Dinhof.

The PHP function generate an image map of the provided svg coord. You can specify a factor number that resize the area and x-y translation numbers to align the map to your image.

<?php

/**
 * $str SVG coordinates string
 * $factor number that multiply every coordinate (0-1)
 * $x translation on the x-axis
 * $y translation on the y-axis
 */
function svg2imap($str, $factor=1, $x=0, $y=0) {

    $res = "";

    $str = str_replace(array(" M ","M ", " C "," z "," z"),array("M","M","C","",""), $str);

    $polygons = explode("M", $str);

    for($i=0; $i<count($polygons); $i++) {

        if($polygons[$i]!="") {

            $res .= "<area shape=\"poly\" coords=\"";

            $coordinates = explode("C", $polygons[$i]);

            foreach( $coordinates as $position ) {

                $noise = explode(" ", trim($position));
                $point = explode(",", $noise[0]);

                for($j=0; $j<2; $j++) {

                    $val = round( $point[$j]*$factor, 0);

                    if($j==0)
                        $res .= ($val + $x).",";
                    else
                        $res .= ($val + $y).",";
                }
            }
            $res .= "\" href=\"link.html\" alt=\"desc\" />";
        }
    }

    return $res = str_replace(",\"","\"", $res);;
}
?>


<?php

$svg = "M 6247.5037,5935.0511 C 6246.0707,5940.7838 6247.5037,5947.9495 C 6243.2043,5959.4149 z";

highlight_string( svg2imap($svg, $factor=0.33, $x=0, $y=0) );

?>

It seems "Gerhard Dinhof" function is not correct and I was wasting time on that. Here you can find a modified version written in c# to convert a simple SVG file into relevant html map codes. Usage: MessageBox.Show(Svg2map("c:\test.svg"))

    // Sample file contents:
    // <?xml version="1.0" encoding="UTF-8" ?>
    // <!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
    // <svg width="739pt" height="692pt" viewBox="0 0 739 692" version="1.1" xmlns="http://www.w3.org/2000/svg">
    // <path fill="#fefefe" d=" M 0.00 0.00 L 190.18 0.00 C 188.15 2.70 186.03 5.53 185.30 8.90 L 0.00 0.00 Z" />
    // </svg>
    private string Svg2map(string svg_file_path)
    {
        string[] svgLines = File.ReadAllLines(svg_file_path);
        string svg = string.Join("", svgLines).ToLower();

        int temp;
        int w = int.Parse(ExtractData(svg,0,out temp, "<svg", "width").Replace("pt", "").Replace("px", ""));
        int h = int.Parse(ExtractData(svg, 0, out temp, "<svg", "height").Replace("pt", "").Replace("px", ""));

        StringBuilder stringToFile = new StringBuilder();
        stringToFile.AppendLine(string.Format("<img id=\"image1\" src=\"image1.jpg\" border=\"0\" width=\"{0}\" height=\"{1}\" orgwidth=\"{0}\" orgheight=\"{1}\" usemap=\"#map1\" alt=\"\" />", w, h));
        stringToFile.AppendLine("<map name=\"map1\" id=\"map1\">");

        byte dataKey1 = (byte)'a';
        byte dataKey2 = (byte)'a';

        int startIndex = 0;
        int endIndex = 0;
        while (true)
        {
            string color = ExtractData(svg, startIndex, out  endIndex, "<path", "fill");
            string svg_input = ExtractData(svg, startIndex, out endIndex, "<path", "d=");
            if (svg_input == null)
                break;

            startIndex = endIndex;

            /// Start..
            stringToFile.Append(string.Format("<area data-key=\"{0}{1}\" shape=\"poly\" href=\"targetpage.html\" alt=\"Description\" coords=\"", (char)dataKey1, (char)dataKey2));
            dataKey1 += 1;
            if (dataKey1 > (byte)'z')
            {
                dataKey2 += 1;
                dataKey1 = (byte)'a';
            }

            bool bFinished = false;
            while (!bFinished)
            {
                string[] points = new string[0];
                string pattern = "";
                svg_input = svg_input.ToUpper().Trim();
                char code = svg_input[0];
                switch (code)
                {
                    case 'M':
                    case 'L':
                        pattern = svg_input.Substring(0, svg_input.IndexOf(" ", svg_input.IndexOf(" ", svg_input.IndexOf(" ") + 1) + 1));
                        svg_input = svg_input.Remove(0, pattern.Length);
                        points = pattern.Trim().Substring(1).Trim().Split(' ');
                        break;
                    case 'C':
                        pattern = svg_input.Substring(0, svg_input.IndexOf(" ", svg_input.IndexOf(" ", svg_input.IndexOf(" ", svg_input.IndexOf(" ", svg_input.IndexOf(" ", svg_input.IndexOf(" ", svg_input.IndexOf(" ") + 1) + 1) + 1) + 1) + 1) + 1));
                        svg_input = svg_input.Remove(0, pattern.Length);
                        points = pattern.Trim().Substring(1).Trim().Split(' ');
                        break;
                    case 'Z':
                        bFinished = true;
                        continue;
                    default:
                        throw new Exception("Invalid pattern");
                }

                int count = points.Length;
                if (count > 4)
                    count = 4;
                for (int i = 0; i < count; i++)
                {
                    var valueParts = points[i].Split('.');
                    // remove part after comma - we don't need this accurancy in HTML
                    stringToFile.Append(valueParts[0]);
                    // comma for seperation - don't worry, we'll clean the last ones within an area out later
                    stringToFile.Append(",");
                }
            }
            stringToFile.AppendLine("\" />");
        }

        // clean obsolete commas - not pretty nor efficient
        stringToFile.AppendLine("</map>");
        stringToFile = stringToFile.Replace(",\"", "\"");


        return stringToFile.ToString();
    }

    private string ExtractData(string data, int startIndex, out int endIndex, string key, string param)
    {
        try
        {
            endIndex = 0;
            int a = data.IndexOf(key, startIndex);
            int a2 = data.IndexOf(key, a + key.Length);
            if (a2 == -1)
                a2 = data.IndexOf(">", a + key.Length);
            int b = data.IndexOf(param, a + key.Length);
            int start = data.IndexOf("\"", b + param.Length) + 1;
            int end = data.IndexOf("\"", start + 1);
            if (b > a2 || start > a2 || end > a2)
                return null;
            int len = end - start;
            endIndex = end;
            string t = data.Substring(start, len);
            return t;
        }
        catch
        {
            endIndex = 0;
            return null;
        }
    }

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