Hello. I am trying to make an interface for 'polygon refinenment'. My starting point is this from the Locator documentation:

DynamicModule[{p = {0.5, 0.5}}, {Graphics[Locator[Dynamic[p]], 
   PlotRange -> 2], Dynamic[p]}]

Here is an example polygon

poly1 = {{0, 0}, {1, 0}, {1, 1}, {0, 1}};

My first thought is

DynamicModule[{p1 = poly1}, {Graphics[Map[Locator,Dynamic[p1]]], Dynamic[p1]}]

But this fails with the message "Coordinate {{0, 0}, {1, 0}, {1, 1}, {0, 1}} should be a pair of numbers, or a Scaled or Offset form." If I get rid of the Dynamic, there is no error.

DynamicModule[{p1 = poly1}, {Graphics[Map[Locator, p1], 
   PlotRange -> 2], Dynamic[p1]}]

and I get four locators that I can move, but of course p1 is now not updated.

Can anyone see how to make a set of locators that update p1? I am wondering if I will have to programmatically create a list of named vertices, and make them all individually Dynamic.

Gareth