My extended sitemap

mxs1.php

<?php

function mxs_flush_rules() {
    global $wp_rewrite;
    $wp_rewrite->flush_rules();
}
register_activation_hook( __FILE__, 'mxs_flush_rules' );
register_deactivation_hook( __FILE__, 'mxs_flush_rules' );

mxs_2.php

<?php

function mxs_add_modules() {
    global $bwp_gxs;
    $bwp_gxs->add_module( 'specials' );
}
add_action( 'bwp_gxs_modules_built', 'mxs_add_modules' );

mxs_3.php

<?php

function mxs_add_rules() {
    return array( 'specials\.xml' => 'index.php?gxs_module=specials' );
}
add_filter( 'bwp_gxs_rewrite_rules', 'mxs_add_rules' );

mxs_4.php

<?php

function mxs_module_dir() {
    return plugin_dir_path( __FILE__ ) . 'modules/';
}
add_filter( 'bwp_gxs_module_dir', 'mxs_module_dir' );

specials.php

<?php

class BWP_GXS_MODULE_SPECIALS extends BWP_GXS_MODULE {

    public function __construct() {
        $this->set_current_time();
        $this->build_data();
    }

    public function build_data() {
        global $wpdb;
        $sql  = "SELECT p.ID, p.post_modified, COUNT( p.ID ) FROM {$wpdb->posts} p, {$wpdb->postmeta} m WHERE p.ID = m.post_id AND m.meta_key IN( 'latitude', 'longitude' ) GROUP BY p.ID, p.post_modified HAVING COUNT( p.ID ) = 2";
        $data = array();
        foreach ( $wpdb->get_results( $sql ) as $post ) {
            $data             = $this->init_data( $data );
            $data['location'] = home_url( '/import/index.php?post_id=' . $post->ID );
            $data['lastmod']  = $this->format_lastmod( strtotime( $post->post_modified ) );
            $data['freq']     = $this->cal_frequency( null, $post->post_modified );
            $data['priority'] = '1.0';
            $this->data[]     = $data;
        }
        return true;
    }

}