convert WKT polys in MySQL to Google Maps polys - mysql

Question

I have a column of WKT POLYGON values in MySQL (I inherited the db). The polys are queried and rendered on Google Maps. Since Google Maps polygon overlay requires an array of points, the previous user converted the WKT values to coordinate pairs and stored them in another column. This actually works rather well, but not well enough.
For one, the conversion was occasionally faulty, and for two, I am looking for ways to make this faster.
Re. the first issue, I have to re-implement this, and am looking for a converter that will convert a WKT poly into a string of coordinates. I am thinking I could use this to either write a stored procedure that will query the WKT column and spit out a string of JSON text that could be readily converted to Google Maps polys, or even preprocess all the WKT polys and store them as text like it is already done, but this time with correct values.
So, I am really looking for a function to convert WKT to a string of its constituent point coordinates, kinda like so
SELECT AsStringOfCoords(WKT_Column) FROM table WHERE condition
where AsStringOfCoords() would be my custom function.

Answer 1

I'd wrote a little C++ program to do MySQL WKT polygons to KML polygons.
This thing works as follows:
Read the information from the database
create a kml document
Rearrange the information and print it out to the file.
You can call the new kml to googlemaps and it shows pretty nice.
The source code is here...
#include <iostream>
#include <string>
/*
* Database includes...
*/
#include <mysql_connection.h>
#include <cppconn/driver.h>
#include <cppconn/exception.h>
#include <cppconn/resultset.h>
#include <cppconn/statement.h>
#include <cppconn/prepared_statement.h>
#include "../iolib/IOCoreFuncs.h"
#include "../iolib/ioconfigurador.h"
using namespace std;
using namespace sql;
using namespace IOCore;
sql::Connection * conectaDB(string dbSvr, string dbUsr, string dbPwd, string dbNombre);
int main(int argc, char **argv) {
string qry, arproc;
Connection * dbCon;
Statement * stmt;
IOConfigurador * miConf;
ResultSet * rs;
//Cargar configuración...
if (argc == 3) {
arproc = argv[2];
} else {
cout << "Using mode: sqltokml <polygon id> <file kml to export>\n";
return 1;
}
dbCon = conectaDB("dbserver", "dbuser"), "dbpasswd", "dbname");
stmt = dbCon->createStatement();
qry = "SELECT name, astext(geoarea) from " + "table name" + " where id = '" + argv[1] + "';";
rs = stmt->executeQuery(qry);
if (rs->rowsCount() > 0) {
string polnombre, polcoords;
string salida;
while (rs->next()) {
ofstream sale;
polnombre = rs->getString(1);
polcoords = rs->getString(2);
salida = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n"
"<kml xmlns=\"http://www.opengis.net/kml/2.2\" xmlns:gx=\"http://www.google.com/kml/ext/2.2\" xmlns:kml=\"http://www.opengis.net/kml/2.2\" xmlns:atom=\"http://www.w3.org/2005/Atom\">\n"
"<Document>\n"
"<name>" + polnombre + ".kml</name>\n"
"<Style id=\"sh_ylw-pushpin3\">\n"
"<IconStyle>\n"
"<scale>1.3</scale>\n"
"<Icon>\n"
"<href>http://maps.google.com/mapfiles/kml/pushpin/ylw-pushpin.png</href>\n"
"</Icon>\n"
"<hotSpot x=\"20\" y=\"2\" xunits=\"pixels\" yunits=\"pixels\"/>\n"
"</IconStyle>\n"
"<LineStyle>\n"
"<color>467f5500</color>\n"
"<width>3</width>\n"
"</LineStyle>\n"
"<PolyStyle>\n"
"<color>46ff5555</color>\n"
"</PolyStyle>\n"
"</Style>\n"
"<StyleMap id=\"msn_ylw-pushpin10\">\n"
"<Pair>\n"
"<key>normal</key>\n"
"<styleUrl>#sn_ylw-pushpin30</styleUrl>\n"
"</Pair>\n"
"<Pair>\n"
"<key>highlight</key>\n"
"<styleUrl>#sh_ylw-pushpin3</styleUrl>\n"
"</Pair>\n"
"</StyleMap>\n"
"<Style id=\"sn_ylw-pushpin30\">\n"
"<IconStyle>\n"
"<scale>1.1</scale>\n"
"<Icon>\n"
"<href>http://maps.google.com/mapfiles/kml/pushpin/ylw-pushpin.png</href>\n"
"</Icon>\n"
"<hotSpot x=\"20\" y=\"2\" xunits=\"pixels\" yunits=\"pixels\"/>\n"
"</IconStyle>\n"
"<LineStyle>\n"
"<color>467f5500</color>\n"
"<width>3</width>\n"
"</LineStyle>\n"
"<PolyStyle>\n"
"<color>46ff5555</color>\n"
"</PolyStyle>\n"
"</Style>\n"
"<Folder>\n"
"<name>" + polnombre + "</name>\n"
"<Placemark>\n"
"<name>" + polnombre + "</name>\n"
"<styleUrl>#msn_ylw-pushpin10</styleUrl>\n"
"<Polygon>\n"
"<tessellate>1</tessellate>\n"
"<outerBoundaryIs>\n"
"<LinearRing>\n"
"<coordinates>\n";
//Coordinates tranformation...
polcoords = polcoords.substr(9, polcoords.size() - 11);
vector< string > lascoords = split(polcoords, ",");
for (unsigned i = 0; i < lascoords.size(); i++) {
salida += lascoords[i].substr(0, lascoords[i].find(" ")) + ",";
salida += lascoords[i].substr(lascoords[i].find(" ") + 1) + ",0 ";
}
salida += "\n</coordinates>\n"
"</LinearRing>\n"
"</outerBoundaryIs>\n"
"</Polygon>\n"
"</Placemark>\n"
"</Folder>\n"
"</Document>\n"
"</kml>";
sale.open(arproc.c_str(), ios::out | ios::app);
sale << salida ;
sale.close();
}
}
rs->close();
stmt->close();
dbCon->close();
}
sql::Connection * conectaDB(string dbSvr, string dbUsr, string dbPwd, string dbNombre)
{
sql::Connection * retval;
sql::Driver *ctrl;
try {
ctrl = get_driver_instance();
retval = ctrl->connect(dbSvr, dbUsr, dbPwd);
retval->setSchema(dbNombre);
} catch (sql::SQLException &err) {
cout<<"Errors... :( "<<err.what()<<"\ngoing out\n";
retval = 0;
}
return retval;
}
I hope this can help you. Is easy to translate this to MySQL stored proc, or use it inside PHP or another languages... I also have some php/javascript scripts to do the same things with points.