There is an extensive help pdf available here: Virtuemart 3.x Radius Shipping Plugin Instruction
Basically what ever the address entered by your customer is looked up in the Google Maps v3 api to find the distance between it and the "source" address. The "source" address is either the VM Vendor address or the address configured in the Virtuemart 3.x Radius Shipping Plugin method admin.
This is to allow a different address say from a delivery center etc. You can have multiple methods with different vendor addresses and each calculated shipping cost will be shown.
If Google can't find the address it will notify by a message so the customer can attempt to try again with an altered address. It is also possible to configure a Shopper field so the customer can fill in their GPS coordinates (latitude & longitude).
If Google does find the address (and extensive testing has proved it has to be radically wrong before it doesn't!) then the address is returned plus a link to a popup map so the customer can check it is correct. A link is provided on this map to a detailed Google map with driving instructions and also in the invoice administration so the directions can be printed out by the store owner.
The shipping calculation as very extensive options - we think we just about thought of everything.
- A minimum "free" delivery area can be specified.
- A maximum delivery radius distance can be specified.
- Imperial or metric can be chosen.
- A simply charge per distance can be specified.
- As this will return prices to 2 decimal places rounding to 0.5 or 1.0 can be selected.
- Weight can be factored into the calculation (open to suggestions here as to how this could be better handled - at the moment it is simply multiplied if over 1).
- Variable Set Fee
You can set up a matrix of distance/fee to cover things like set costs for long distance (this is especially useful for service deliveries etc).
- Sector calculations
You can set up as many distance sector/price matrix as you need so that shipping is charged in set blocks depending on distance.
- Fixed set fee
This can be used a minimum charge - all these settings can be used individually or in combination.
Of course all the normal shipping plugin filters are also available such as countries, min/max weight, min/max product numbers, min/max order amount.
And please remember we are always here to help - we pride ourselves on our customer support so fell free to ask via our Support Page.
N.B. There may be further coding necessary if you are using a 3rd party OPCheckout extension. The problem is the majority of these extensions do not re-submit the address if it is changed - only the country .