[Manifold-l] Projection Query - regarding Map Grid of Australia1994, Zone 54...

[Graeme Greenwood]

Hi Chris,

 

The help topic for Edit - Assign Projection states in part "..With images or
surfaces, the Local offset stores the offset to the left-bottom corner of
the left-bottom pixel of the image or surface.". That is the answer to your
question. For your own enlightenment, try having the status bar display
projected coordinates (tools / options / status bar / choose projected from
the drop down). Then with your surface component open and displayed at its
full extent, move your cursor to the lower left / southwest corner and note
the displayed location. Jot the values down. Then check your surface'
projection - the two values will coincide (well, within a screen pixel).

 

Hope this helps, good luck!

 

Graeme Greenwood

MapMakers Australia

Ph (03) 6334 5620

Fax (03) 6312 5005

Mob 0439 760 169

 <mailto:Graeme at mapmakers.com.au> Graeme at mapmakers.com.au 

 <http://www.mapmakers.com.au/> www.mapmakers.com.au 

 

  _____  

From: manifold-l-bounces at lists.directionsmag.com
[mailto:manifold-l-bounces at lists.directionsmag.com] On Behalf Of Medlin,
Chris (DWLBC)
Sent: Wednesday, 8 November 2006 10:41 AM
To: manifold-l at lists.directionsmag.com
Subject: [Manifold-l] Projection Query - regarding Map Grid of
Australia1994, Zone 54...

 

Hi List, 

Resend of msg sent to "manifold-l at lists.directionsmag.com" on Nov 6, 2006.
Is the list working properly?  Moving right along...

I recently imported an ESRI Grid into Manifold (v 6.5 build 408) as a
Surface.  The surface is a lidar derived digital elevation model of part of
Western Victoria (Australia) with a cell size of 10 metres.  The projection
used by this data is the Map Grid of Australia 1994 (zone 54).  Based on the
Geocentric Datum of Australia 1994 (GDA94) the Map Grid of Australia 1994
utilises a Universal Tranverse Mercator projection (with 6 degree zones)
with a scale factor of 0.9996 at the central meridien and a false northing
of 10,000,000 and a false easting of 500,000.  Map units are metres.

What I can't understand is why I see the appearance of a 'local offset' of
495000.00 in X and a local offset of 5880000.00 in Y.  What is this 'local
offset' about?  I've not come across it before with respect to this
projection.  Having read the Manifold help with regards to the 'local
offset' parameter, I still don't understand why these values are appearing.
If I use the Edit > Projection > Current Projection dialogue to set these
'local offset, values to zero, then the coordinates that I see as I move the
cursor around the surface are clearly incorrect (eg. 22967E 19276N).

Can anyone provide some insight into this for me? 

Thanks, 

Chris Medlin 

========================================================== 
Chris Medlin 
Geographic Information Systems (GIS) Officer 
Resource Information - Knowledge and Information Division 
Department of Water, Land and Biodiversity Conservation 
Level 3, 25 Grenfell St, ADELAIDE 
GPO Box 2834, ADELAIDE, SA, 5001 

Phone: (08) 846 37981;  Fax: (08) 846 37900;  Mobile Ph: 0410 413 616 
Email: chris.medlin at state.sa.gov.au 

 

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