Reading Template Variables in a Snippet?

$id = $modx->resource->get('id'); // This page's ID
$tv = $modx->getObject('modTemplateVar',array('name'=>'name_of_my_tv'));
$my_tv_value = $tv->getValue($id);

$tv = $modx->getObject('modTemplateVar', array('name' => 'EventCategory'));
$eventCategory = $tv->renderOutput($eventId);

$val = $resource->getTVValue('TvName');
$val = $resource->getTVValue($id); // ID of the TV, not the resource -- this is faster)