dCaldav

Support is available on my badzilla forum.

How you obtain the URL for your caldav server collection is dependent on your server. You should refer to the user documentation of the server you are using. However the following hints are available below to help you:

OSAF Chandler Hub

Log in to your account, click on blue downward arrow next to the collection you wish to publish, click on invite, click on view only, click on CALDAV. A popup window will appear - select the URL and copy it. NOTE: Chandler Hub uses a ticket authentication method, so your URL should look like https://hub.chandlerproject.org/dav/collection/{unique number}?ticket={unique number}

dCaldav needs the URL of your Google Calendars collection to work correctly. To obtain this URL, log into your Google account.

Click on Settings->Calendars->{name of your calendar}->{Calendar Address: ical button}

This will launch a popup window with your URL. Copy this URL by selecting it then right click and copy.

If your calendar is not marked as 'Public', you need to do this first. Click on Settings->Calendars->Shared: Edit Settings. Tick on 'Make this calendar public'

In an ideal world, the protocols I have used whilst developing jCaldav to obtain remote calendar ics files would be consistent. Unfortunately this is not the case, although I hasten to add that this is totally transparent to the end-user, and only minimally inconvenient for a Joomla website administrator. 

The problem is Google don't make life easy for a developer to interface with their calendaring system. They have published a PHP API which on the face of it should provide the ideal mechanism for me. BUT the API requires the installation of the Zend MVC to work - which means an additional dependency for anyone installing my component. Secondly, I haven't tested Zend with Joomla and don't know if the Zend MVC would co-exist with the Joomla MVC.

The alternative would be to develop my own Google API. This itself isn't easy due the complex authentication code I would need to write just for Google connectivity. Developing, testing and maintaining this code quite frankly isn't worth the effort considering there are other ways of skinning this cat. Google allow calendar files to be downloaded using a straight HTTP 1.1 GET request. Thankfully this is extremely easy to implement and as such is the process my code uses. 

The downsides to this approach are minimal. The Google Calendar needs to be marked as a 'public' calendar - which as you will be publishing the calendar's contents on your site, is no hardship, and whilst configuring the collection in Joomla you need to click the radio button marked 'Google Calendars'. And that's it! Oh, also check out the FAQ entry for obtaining your Google Calendar URL.

The module is installed just like any other,  by copying and installing into sites/all/modules

The component does not support all the features of iCalendar. In particular, the only components currently supported are:
VEVENT
VTIMEZONE
It is hoped to add VFREEBUSY soon, but there are no plans to include support for VTODO or VJOURNAL
Currently, recurring events are not supported.

To set the frequency of update of a collection, you should set the timeout parameter. That does NOT actually mean the collection will be updated after exactly timeout seconds. Instead, it will be updated the next page update after timeout seconds. If the connection to the remote collection fails, the component will simply use any existing data to hand and then wait again timeout seconds.