function red_silk_attachment_field_data ( $form_fields, $post ) {
   $form_fields[ 'rs-horizontal-pos' ] = array(
    'label' => 'Horizontal Position',
    'input' => 'text',
    'value' => get_post_meta( $post->ID, 'rs_horizontal_pos', true ),
    'helps' => 'Far Left is 0, Right is 100.',
);

   $form_fields[ 'rs-vertical-pos' ] = array(
    'label' => 'Vertical Position',
    'input' => 'text',
    'value' => get_post_meta( $post->ID, 'rs_vertical_pos', true ),
    'helps' => 'Top is 0, bottom is 100.',
);

   $form_fields[ 'rs-location' ] = array(
    'label' => 'Location',
    'input' => 'text',
    'value' => get_post_meta( $post->ID, 'rs_location', true ),
    'helps' => 'Address or City',
);

return $form_fields;
}
add_filter( 'attachment_fields_to_edit', 'red_silk_attachment_field_data', null, 2 );

function red_silk_attachment_field_data_save ( $attachment, $post ) {

// Horizontal position check and update.
if( isset( $attachment['rs_horizontal_pos' ] ) ) {
    update_post_meta( $post['ID'], 'rs_horizontal_pos', sanitize_text_field($attachment[ 'rs_horizontal_pos' ] ) );
} else if ( !isset( $attachment[ 'rs_horizontal_pos'] ) ) {
    update_post_meta( $post['ID'], 'rs_horizontal_pos', null );
}

// Vertical position check and update
if( isset( $attachment[ 'rs_vertical_pos' ] ) ) {
    update_post_meta( $post['ID'], 'rs_vertical_pos', sanitize_text_field($attachment['rs_vertical_pos'] ) );
} else if ( !isset( $attachment[ 'rs_vertical_pos'] ) ) {
    update_post_meta( $post['ID'], 'rs_vertical_pos', null );
}

if( isset( $attachment[ 'rs_location' ] ) ) {
    update_post_meta( $post['ID'], 'rs_location', $attachment[ 'rs_location' ]  );
   }
}

add_filter( 'attachment_fields_to_save', 'red_silk_attachment_field_data_save', null, 2 );