Group by terms in a single vocabulary when multiple vocabularies are present?

I have a content type with a variety of vocabularies assigned to it, so that nodes will have terms from multiple vocabularies at once. I need a way to show a pie chart group the nodes by the terms in only one of the vocabularies at a time. Unfortunately, I can't seem to find a way to do that. Instead, it shows the terms from all vocabularies, sorted by vocab. Here's my views code:

$view = new view;
$view->name = 'dped_browser_charts';
$view->description = '';
$view->tag = '';
$view->view_php = '';
$view->base_table = 'node';
$view->is_cacheable = FALSE;
$view->api_version = 2;
$view->disabled = FALSE; /* Edit this to true to make a default view disabled initially */
$handler = $view->new_display('default', 'Defaults', 'default');
$handler->override_option('fields', array(
  'nid' => array(
    'id' => 'nid',
    'table' => 'node',
    'field' => 'nid',
  ),
  'tid' => array(
    'label' => '',
    'alter' => array(
      'alter_text' => 0,
      'text' => '',
      'make_link' => 0,
      'path' => '',
      'link_class' => '',
      'alt' => '',
      'prefix' => '',
      'suffix' => '',
      'target' => '',
      'help' => '',
      'trim' => 0,
      'max_length' => '',
      'word_boundary' => 1,
      'ellipsis' => 1,
      'html' => 0,
      'strip_tags' => 0,
    ),
    'empty' => '',
    'hide_empty' => 0,
    'empty_zero' => 0,
    'type' => 'separator',
    'separator' => ', ',
    'link_to_taxonomy' => 1,
    'limit' => 1,
    'vids' => array(
      '1' => 1,
      '2' => 0,
      '3' => 0,
      '4' => 0,
      '5' => 0,
    ),
    'exclude' => 0,
    'id' => 'tid',
    'table' => 'term_node',
    'field' => 'tid',
    'relationship' => 'none',
  ),
  'name' => array(
    'label' => 'Term',
    'alter' => array(
      'alter_text' => 0,
      'text' => '',
      'make_link' => 0,
      'path' => '',
      'link_class' => '',
      'alt' => '',
      'prefix' => '',
      'suffix' => '',
      'target' => '',
      'help' => '',
      'trim' => 0,
      'max_length' => '',
      'word_boundary' => 1,
      'ellipsis' => 1,
      'html' => 0,
      'strip_tags' => 0,
    ),
    'empty' => '',
    'hide_empty' => 0,
    'empty_zero' => 0,
    'link_to_taxonomy' => 0,
    'exclude' => 0,
    'id' => 'name',
    'table' => 'term_data',
    'field' => 'name',
    'relationship' => 'none',
  ),
  'name_1' => array(
    'id' => 'name_1',
    'table' => 'vocabulary',
    'field' => 'name',
  ),
  'views_sql_groupedfields' => array(
    'label' => 'Group By Fields',
    'alter' => array(
      'alter_text' => FALSE,
      'text' => '',
      'make_link' => FALSE,
      'path' => '',
      'alt' => '',
      'link_class' => '',
      'prefix' => '',
      'suffix' => '',
      'target' => '',
      'trim' => FALSE,
      'max_length' => '',
      'word_boundary' => TRUE,
      'ellipsis' => TRUE,
      'strip_tags' => FALSE,
      'html' => FALSE,
    ),
    'empty' => '',
    'hide_empty' => 0,
    'empty_zero' => 0,
    'exclude' => '1',
    'id' => 'views_sql_groupedfields',
    'table' => 'views_groupby',
    'field' => 'views_sql_groupedfields',
    'relationship' => 'none',
    'views_groupby_fields_to_group' => array(
      'name' => 'name',
      'name_1' => 'name_1',
    ),
    'views_groupby_sql_function' => 'count',
    'views_groupby_fields_to_aggregate' => array(
      'nid' => 'nid',
    ),
    'views_groupby_field_sortby' => 'nid',
    'views_groupby_sortby_direction' => 'desc',
    'override' => array(
      'button' => 'Override',
    ),
  ),
));
$handler->override_option('filters', array(
  'type' => array(
    'operator' => 'in',
    'value' => array(
      'application' => 'application',
    ),
    'group' => '0',
    'exposed' => FALSE,
    'expose' => array(
      'operator' => FALSE,
      'label' => '',
    ),
    'id' => 'type',
    'table' => 'node',
    'field' => 'type',
    'override' => array(
      'button' => 'Override',
    ),
    'relationship' => 'none',
  ),
));
$handler->override_option('access', array(
  'type' => 'none',
));
$handler->override_option('cache', array(
  'type' => 'none',
));
$handler->override_option('style_plugin', 'charts');
$handler->override_option('style_options', array(
  'views_charts_series_fields' => array(
    'tid' => 'tid',
  ),
  'views_charts_x_labels' => 'tid',
  'width' => '500',
  'height' => '700',
  'engine' => 'bluff',
  'type' => array(
    'bluff' => 'pie',
  ),
  'wmode' => 'window',
  'y_min' => '0',
  'y_legend' => '',
));
$handler = $view->new_display('page', 'Page', 'page_1');
$handler->override_option('path', 'chart');
$handler->override_option('menu', array(
  'type' => 'none',
  'title' => '',
  'description' => '',
  'weight' => 0,
  'name' => 'navigation',
));
$handler->override_option('tab_options', array(
  'type' => 'none',
  'title' => '',
  'description' => '',
  'weight' => 0,
  'name' => 'navigation',
));