The center of the projection, or requested image, should be somewhat
close to a UTM zone for that center. If you start using a UTM
projection too far from the central meridian of a zone, the accuracy
of the coordinate transformations suffer. When wandering into the
neighboring zone area, the accuracy of the coordinates deteriorate.
Using a center point on the opposite side of the earth from a UTM zone
really won't have meaning. Northing and easting values are offsets
from the real x/y origin of the zone of the projection (the central
meridian and I think, the equator, someone correct me if I'm wrong),
the basis for the UTM meter coordinates.
So the center should be chosen with the proper UTM projection in mind.
You can use the UTMPoint to figure out which zone is most appropriate
for a given lat/lon.
- Don
On Fri, Feb 25, 2011 at 10:12 AM, Greg Jewell <greg17_at_jewell.net> wrote:
> Based on Tore's comments, it sounds like it may be a bad idea to change the
> northing and easting values if connected to WMS. Is my interpretation
> correct? I have an application that defines an initial center, but then may
> switch to the other side of the globe. In the cases where the center
> changes by a great amount, the rendering in UTMProjection becomes very
> "interesting" since the northing and easting values aren't changed. Putting
> a new projection into the map bean every time the center changes is my
> current solution. Is this bad? If so, do you have any suggestions?
>
>
>
> On Fri, Feb 25, 2011 at 8:37 AM, Don Dietrick <dfdietrick_at_gmail.com> wrote:
>>
>> This is a good point. Greg, changing the "center" of this projection is
>> not the same thing as changing the northing and easting. OM5 lets you
>> change the n&e, but that just defines the projection parameters. The view is
>> controlled by the center.
>>
>> -- Don
>>
>> On Feb 25, 2011, at 3:05 AM, Tore Halset <halset_at_pvv.ntnu.no> wrote:
>>
>> > Hello.
>> >
>> > For the WMS, it is important that the UTMProjection can be used with a
>> > center coordinate outside of the natural UTM zone number. That is, they
>> > select a fixed EPSG-code and pan outside of the UTM zone area.
>> >
>> > Regards,
>> > - Tore.
>> >
>> > On Feb 24, 2011, at 22:56 , Don Dietrick wrote:
>> >
>> >> Hi Greg,
>> >>
>> >> This was probably an oversight as the OM5 beta has accessors for those
>> >> UTMProjection parameters.
>> >>
>> >> - Don
>> >>
>> >> On Thu, Feb 24, 2011 at 4:33 PM, Greg Jewell <greg17_at_jewell.net> wrote:
>> >>> Hello,
>> >>>
>> >>> I have a question about the implementation of UTMProjection in OM
>> >>> 4.6.5.
>> >>> The fields zone_number, isnorthern, and ellps are set in the
>> >>> constructor.
>> >>> These values are used in several methods of the class. However, a
>> >>> later
>> >>> change to the center of the projection never updates these values.
>> >>> The
>> >>> fields are private, and setCenter(LatLonPoint llp) isn't overridden.
>> >>> Was
>> >>> this intentional, or just an oversight? Right now, every time the
>> >>> center
>> >>> changes (through user panning or other means), I create an entirely
>> >>> new
>> >>> UTMProjection instance and give it to the MapBean. The other option
>> >>> is to
>> >>> subclass UTMProjection, but I'd have to essentially copy the entire
>> >>> class
>> >>> and add an overridden setCenter method.
>> >>>
>> >>> If this behavior was intentional, will my workarounds cause any
>> >>> problems?
>> >>>
>> >>>
>> >>> Thanks,
>> >>> Greg Jewell
>> >>>
>> >>>
>> >>
>> >> --
>> >> [To unsubscribe to this list send an email to "majdart_at_bbn.com"
>> >> with the following text in the BODY of the message "unsubscribe
>> >> openmap-users"]
>> >>
>> >
>
>
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Received on Fri Feb 25 2011 - 10:42:14 EST