Jansepar.com

Hey guys!
So, last week I set out some goals for myself to get com­pleted this past week. I’ll re-post them here:

Have the arti­cle from Andrew read so I can be brought up to speed on some of the OGR ter­mi­nol­ogy.
Have OGR built with Opti­miza­tion on.
Have a sam­ple piece of C code going that demon­strates KML.
Hope­fully have the details from Chuck on what the changes are from list­ing the SQL func­tions. If this pans out, try to get a stub func­tion going that out­puts “Hello KML!”

I am proud to say I’ve achieved my goals! First thing that I did was to get the build for OGR going, so I will dis­cuss that first.

OGR

OGR is an open source library OGR is actu­ally a sub­set of the GDAL pack­age, so in order to build GDAL, it meant hav­ing to build OGR. Here is a link to the GDAL source:

wget http://download.osgeo.org/gdal/gdal172.zip

Andrew wanted to know how large OGR would be once opti­miza­tion was turned on, and so I set out to find out this info. I didn’t exactly know what it meant for opti­miza­tion to be on — but I learned that it meant that it was a build of OGR that would be pro­duc­tion ready, that min­i­mized the amount of debug data. After doing a build of OGR, it was deemed an accept­able sized library to include in Ingres! Here were the steps I used to build OGR:

export CFLAGS=-O2
export CXXFLAGS=-O2

And the configure:

./configure –prefix=/usr/local \
> –with-threads \
> –with-ogr \
> –with-geos \
> –without-libtool \
> –with-libz=internal \
> –with-libtiff=internal \
> –with-geotiff=internal \
> –without-gif \
> –without-pg \
> –without-grass \
> –without-libgrass \
> –without-cfitsio \
> –without-pcraster \
> –without-netcdf \
> –without-png \
> –with-jpeg=internal \
> –without-gif \
> –without-ogdi \
> –without-fme \
> –without-hdf4 \
> –without-hdf5 \
> –without-jasper \
> –without-ecw \
> –without-kakadu \
> –without-mrsid \
> –without-jp2mrsid \
> –without-bsb \
> –without-grib \
> –without-mysql \
> –without-ingres \
> –without-xerces \
> –without-expat \
> –without-odbc \
> –without-curl \
> –without-sqlite3 \
> –without-dwgdirect \
> –without-idb \
> –without-sde \
> –without-perl \
> –without-php \
> –without-ruby \
> –without-python \

Once I was able to com­pile, build, and install it, I was able to fol­low some of the sam­ple API stuff in OGR.

KML

The ques­tions sur­round­ing KML have been inter­est­ing, its been on and off as to which library to use to con­vert well known binary (WKB) into KML. The orig­i­nal idea was to use OGR, but then when talk­ing to the OGR com­mu­nity, they said that it may not be thread safe.. We started doing research into what else we could use, maybe just directly using libkml. If we were to go this route then we would have to cre­ate the algo­rithm that con­verts WKB into some­thing that we can enter into the libkml library. We went back to the OGR route, and with the help of Frank Warmer­dam, we were able to get WKB con­verted into KML! My biggest chal­lenge dur­ing this process was learn­ing how to com­pile and build exe­cuta­bles in C, using dynamic libraries, but after learn­ing, it was really quite sim­ple. I just haven’t done very much C

Here is the code that con­verted WKB into KML incase any­one wants to use this themselves:

#include “ogr_api.h”

int main()
{
OGR­Err eErr;
OGR­Ge­om­e­tryH hGeom = NULL;
char *kml = NULL;
unsigned char *wkb_buffer = “\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x14@\x00\x00\x00\x00\x00\x007@”;

eErr = OGR_G_CreateFromWkb( wkb_buffer, NULL, &hGeom, –1 );
if( eErr == OGRERR_NONE )
{
kml = OGR_G_ExportToKML( hGeom, “???I do not know what this is” );
OGR_G_DestroyGeometry( hGeom );
printf( “kml = %s\n”, kml );
//CPLFree( kml );
}
else if( eErr == OGRERR_NOT_ENOUGH_DATA )
{
printf(“error1”);
}
else if( eErr == OGRERR_UNSUPPORTED_GEOMETRY_TYPE )
{
printf(“error2”);
}
else if( eErr == OGRERR_CORRUPT_DATA )
{
printf(“error3”);
};

}

The next step now is to imple­ment the asKML func­tion within the Ingres source code! Right now one of the devel­op­ers Chuck is still work­ing on reviv­ing the instruc­tions to do this, but once he is fin­ished, I will be good to go!

Shawn