Petiar.sk: How to add and process location CCK field on Drupal form programatically?

Recently (actually, an hour ago) I have been creating a Drupal module which should create a form and process it. The purpose of this form was to replace the node add form so the only process action has to be the node_save call. This was quite simple, however, this form should contain gmap widget as a coordinate chooser. It took me a while to get it work so I would like to share my knowledge.

Firstly, how to we display the coordinate chooser as a form element. After long googling I have found a function gmap_set_location. It accepts three parameters. The first one, $map, is a gmap macro which you want to use to display the map coordinate chooser. The second one, &$form, is a reference to the particular form, you want to add this widget to. The third parameter is an array containing names of fields storing information to process. latitude and longitude keys are required, the address key is optional. So the form (or the location piece) itself will look like this:

$map_macro = '[gmap|id=usermap|center=0,30|zoom=13|width=400px|height=400px]';
$form = array();
 
$form['title'] = array(
	'#type' => 'textfield',
	'#title' => t('Location title'),
	'#required' => TRUE,
);
 
$form['latitude'] = array(
  '#type' => 'hidden',
  '#default_value' => '48.15509285476016',
);
 
$form['longitude'] = array(
  '#type' => 'hidden',
  '#default_value' => '17.105712890625',
);
 
$form['gmap']['#value'] = gmap_set_location($map_macro, $form, array('latitude'=>'latitude','longitude'=>'longitude'));

Now lets go to process the form. We can break down the processing to two steps - save the location and save the node. And that's very easy, the only thing we need to know is, how to save the location. Fortunately, there is a location_save function, which does all the dirty job for us. It accepts an array containing all the location information. As we want to store only the coordinates, it would like somehow like this:

$location = array();
$location['latitude'] = $form_state['values']['latitude'];
$location['longitude'] = $form_state['values']['longitude'];
$location['inhibit_geocode'] = TRUE;
$lid = location_save($location);

When the location_save function finishes successfully, it will return the location id ($lid). With the new node you will save it like this:

$node->locations[0]['lid'] = $lid;
 
// other stuff
 
node_save($node);