To subscribe to Cal4D published calendars, the Cal4D Manual states:

In the URL field enter what will be last segment of the subscription URL, e.g. "mySchedule.ics". Cal4D will parse the URL "https://<myIPaddress>/CalSRVR/mySchedule.ics" or "webcal://<myIPaddress>/CalSRVR/mySchedule.ics" or "webcals://<myIPaddress>/CalSRVR/mySchedule.ics".

With regards to the "myIPaddress" element of the URL, there are two situations that must be taken into consideration...

First, if Cal4D is going to publish calendars on a "closed" LAN only certain applications will be able to access the calendars. Apple’s iCal™ and Microsoft’s Outlook™ (version 7 or greater) applications will be able to subscribe to Cal4D published calendars. In this case the "myIPaddress" will simply be the local network IP address of the computer hosting the 4D Web Server. Google Calendars cannot subscribe to these Cal4D published calendars because the Google servers cannot access the 4D Web Server.

Second, if Cal4D is going to publish calendars on a network that has an IP address available to the external world, then Apple’s iCal™ and Microsoft’s Outlook™ (version 7 or greater), and Google Calendars can subscribe. In this case the "myIPaddress" element of the URL should be IP address of the network router that acts as the network gateway to the World Wide Web. For Google Calendars this is a so that the Google servers can request the calendar from the Cal4D calendar server. Not only will this facilitate users subscribing to Cal4D published calendars from Google Calendars but also for those subscribers using Apple’s iCal™ and Microsoft’s Outlook™.