[OpenLayers-Users] projection transform, not working on first load?

[christopher.schmidt at nokia.com]

On Jun 22, 2010, at 7:42 AM, ext Ken Sanderson wrote:

> So I am using a few transforms with my openlayers mapping application. 
> Generally speaking it works fine, however it seems to never transform 
> properly when the application first loads.
> 
> So for example I have a database with EPSG:26911 points in it. I create 
> a point with those coordinates, then transform them to 900913 before 
> adding them as a feature to a vector layer.
> 
> Points will not show up, but if I put alert(point.x); then I will see 
> that the very first point will give me the UTM coordinate, but then 
> after that they will all be transformed appropriately and they will 
> display on the map and the alert gives me the web Mercator coordinate. 
> Without the alert though it doesnt 'trigger' it to work properly and 
> none of the points will be displayed.

 * OpenLayers only knows how to transform to/from EPSG:900913/EPSG:4326
   by default.
 * With proj4js support, it can support more projections, but only based
   on the available definitions.
 * If proj4js does not have projection information, it will attempt to 
   load http://spatialreference.org/ref/epsg/26911/proj4js/ into your
   page.
 * This operation is non-blocking -- meaning proj4js has no way to know
   when it is done and 'pause'.

As a result, when you first attempt to transform, proj4js will try to 
load http://spatialreference.org/ref/epsg/26911/proj4js/ , it will take
a second, and in the meantime, your transform will do nothing.

The fix to this is to include:

  Proj4js.defs["EPSG:26911"] = "+proj=utm +zone=11 +ellps=GRS80 +datum=NAD83 +units=m +no_defs";

directly in the source of your page.

In general, it's polite to do this anyway so as to not hit sr.org for 
every page load.

Best Regards,
-- 
Christopher Schmidt
Nokia