title: Determine Time Offset given Olson TZID and local DateTime?
body: <p>I need to <strong>determine Time Offset given Olson TZID of an event and a DateTime of an event</strong>.</p>
  
  <p>I suppose I can do it with a help of Noda Time, but I'm new here and need help - an example of actual API call sequence to perform this task.</p>
  
  <p>A few more details of what we're using and doing.</p>
  
  <ol>
  <li>We're running ASP.NET + SQL Server based Web site. Users of our site enter and save events which are happening at various locations. For each event Lat/Long and DateTime with time offset (of that event) are among required fields.</li>
  <li>There are various scenarios of data entry, sometimes Lat/Long is entered first, sometimes DateTime is. System allows to determine Lat/Long from an address or a map point. We want Time Offset to be consistent with Lat/Long in most of the cases because we normally expect DateTime being entered as local to that event.</li>
  <li>We use SQL Server DateTimeOffset field to store data.</li>
  <li>We don't want to depend on third-party web services to determine an offset, but prefer our system to do that.</li>
  </ol>
  
  <p>I'm free to download and use any necessary tools or data. I already downloaded shapefiles from <a href="http://efele.net/maps/tz/" rel="nofollow">http://efele.net/maps/tz/</a> and used Shape2SQL <a href="http://goo.gl/u7AUy" rel="nofollow">http://goo.gl/u7AUy</a> to convert them to SQL Server table with TZIDs and GEOMs.
  <br><strong>I know how to get TZID from Lat/Long</strong> by querying that table.
  <br>What I need, again, is to <strong>determine Time Offset from TZID and DateTime</strong>.</p>