[worldKit-dev] use of GDA94 in world kit

[Mikel Maron]

Hi Matt, 

Picking this up again. Yes worldKit needs a reprojected image, as well as the extents of that image. I suspect Google Earth also needs a reprojected image, and is simply using the original .. this may look good enough, though slightly imprecise. The smaller the extent of the image, the less effect the reprojection will actually have. Does this make sense? Sorry, didn't actually get to take a look at the KML, bandwith in my current location is severely limited.

Best
Mikel

----- Original Message ----
From: Matt McClelland <matt at wildcolour.com>
To: Discussion of worldKit use and development <worldkit-dev at lists.brainoff.com>
Sent: Thursday, June 15, 2006 12:32:25 AM
Subject: Re: [worldKit-dev] use of GDA94 in world kit

Thanks Mikel
  
 OK my head is about to explode - I have not done this much math since ....  well, every really.
  
 I found an article on redearn formula that is used to convert between GDA9A Northing and easting to LAT and LONGS.  I then wrote and and PHP file to convert "BBOX=" values to northings and eastings to request the correct file.  And it seems to work well.  (there is a problem with zooming west of King island - as the server does not seem to allow request outside of zone 55 - so don't go west of king Island. 
  
 The script outputs a KML file for google earth to create an overlay - seems to work well.  But for this to work with world kit I think I need to pass an image not a xml file with the location of the image.  So next step is to pull out the PHP book again and learn how to pass and image file - unless you have a better idea. (I would rather not have to load the image into the server and then send it again - this would be very slow) 
  
 The script still have a little bit of tweeking you may notice the top of the map is stretched out a bit.
  
 I have attached the KML file to play with  --  remember to zoom right into Tasmania Australia (that is under downunder)
  
 Matt  :)
 

 
 On 6/14/06, Mikel Maron <mikel_maron at yahoo.com> wrote: Hey Matt

GDA94 [Geocentric Datum of Australia 1994 (GDA94)]   is a UTM projection .. chosen since it will produce less distorted images over Australia than unprojected lat/long imagery. 

I am not aware of an easy way either, but am aware of A way. http://brainoff.com/weblog/2006/06/02/1157 describes a bit of what we did to reproject imagery of Indonesia into unprojected lat/long. It may have enough pointers to get going. You will have to have a "world file" for this image prepared. 

Let me know how it goes, we can hash it out.

Mikel

----- Original Message ----
From: Matt McClelland
To: Discussion of worldKit use and development
Sent: Friday, June 9, 2006 8:13:53 PM
Subject: [worldKit-dev] use of GDA94 in world kit 

one data source that I am wanting to use with worldkit is in a GDA94 system (as apposed to normal lat and longs used in worldkit)  I really don't understand why there are different systems, but hay.

I am not aware of any easy way to convert between GDA94 and lat long, so I am a bit stuck in how to intergrate this into world kit. 

Here is a url with a sample image

 http://www.thelist.tas.gov.au/listmap/servlet/listmapGetMap?minx=440000&miny=5371500&maxx=446000&maxy=5376000&iwidth=1600&iheight=1600&layers=26,194,22,19,18,2,197,196,39,40,198,27,28,195,20,202,10,25&imageno=41&grid=true 

you can see the easting and northing figures in the minx miny (and maxx maxy)  (this map source is for the state of tasmania in Australia and is protected under copyright, ra ra ra)

Any ideas???

 thanks

Matt  :)
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