[Xastir] Maps, again!

[Gerry Creager n5jxs]

Aha.  the pages referenced below simply did the leg-work for you.

Curt,  We need to talk about postgis again.  Some of this pain can be 
dealt with directly therein.

John,  Find the metadata associated with the images you have gotten. 
See what the center point and the corners are supposed to be at... 
you've pretty well gotten there.  Identify the datum associated with the 
geodetic position, and the coordinate system.  Determine if the image is 
appropriately rectified.  Also, in the registration process the degree 
of affine used (number of points) should be given.  Finally, did the 
supplier project the image to match a particular maptype?  This is 
uncommon but not unheard of.  If so, you may have to reproject it, which 
is a pain.  It'll likely mean, more to the point, doing a rubber-sheet 
re-registration/rectification of the image which will introduce some 
distortion.

73, gerry

John Ronan wrote:
> Hi There again,
> 
> I'm about to head up to my folks place (30 miles or so - EI7IG-9), I've 
> been busy putting in the sections of the map so that I can see it 
> afterwards.
> 
> Each Tiff is 4724 x 4724 and the boundarys are the lines in the map.  So 
> I've been using
> http://www.megalithomania.com/conversion/
> 
> To convert from Irish Grid to Degrees Minutes Seconds and then
> http://www.uky.edu/KGS/gis/converter.htm
> 
> to convert to decimal Lat/Long.
> 
> I'm wondering what others use to convert to decimal lat/long as I'm 
> seeing gaps/slight overlaps in the pictures.
> 
> Tomorrow I'll check it out a bit more, but It looks to me like a 
> rounding error of some sort as two of the maps (I've done a square) that 
> I have done have the northeast/southwest corners at the correct point.
> 
> Bearing in mind that I know little or nothing about maps except that 
> they are all a 'projection' of some sort.  Can I assume that as I go 
> further and further from the 'point' mentioned above that I will begin 
> to see gaps in the projection.
> 
> Thanks for the help (and a great application)
-- 
Gerry Creager -- gerry.creager at tamu.edu
Network Engineering -- AATLT, Texas A&M University	
Cell: 979.229.5301 Office: 979.458.4020
FAX:  979.847.8578 Pager:  979.228.0173
Office: 903A Eller Bldg, TAMU, College Station, TX 77843