InfoPath Dev

Hello,
I am running into a problem with data validation. I have 2 fields that users have to enter latitude and longitude. The data type is "double, not required"(<xsd:element name="PHYS_LOC_begin_latitude" nillable="true" type="xsd:double"/>). I need this field to be validated but not required. I've used the "data validation" button and the field then becomes required. Is there a workaround for this? Can anyone help?

What about putting a default value in the field that you can than use in a rule to exclude validation if the default value is not changed?.

Any ideas on how that might be done? I've tried it with no success....

Add a rule that fires when the field is changed (this is the default, no condition rule). For this rule, add an action to set another value (ideally in a secondary data source). Use that value to conditionally enable or disable validation on the original field. Good luck Tracy!

Why not just add to the data validation  AND Lattitude "is not blank" to whatever you already have?