Rasters, TileIndex and Shapefiles - Oh My! Really Confused

[Christopher Harris]

Thanks again, Ed.  I need to clear up some things that I guess I didn't make clear.

I know that a world file provides georeferencing.  I meant to say that I had a .gif that had no georeferencing info associated with it, and then added one.  From there I got my initial app to work (displaying the big map).

One thing I omitted was that the little .gifs (tiles), when assembled, make up a different big map pic then the one where mentioned :
“it uses one .gif
(the big map pic), attaches the big map to the globe via a world file. 
That big map .gif had no georeferencing info attached to it."Before I had a pic of a large section of a college campus.  Now I have a pic of the entire campus, but in little tiles.
I know Mapserver makes maps and not pics too.  I probably just worded something wrong.
"So – what do you know about these
images?  Do you really have a world file that correctly describes your big GIF
image?  Do you know exactly how the little images were created from the big
image?  If so, you should be able to figure out how to generate world files for
each individual image.  If not, you’ll need to get that information for
your big image."

Yes, I have a world file, but it's for the pic that shows a large section of the campus - not for the big pic that is the sum of the little pics.


Ok, so then I have to have a world file for every little tile, but before that I need to correctly set up the world file for the big pic, which I guess I'll need to assemble in Photoshop.  Does that sound right?  I can do it, it's just a bit tedious lining up the tiles and such.  Also, how do you correctly align a pic of some map on the globe.  I've been using Google Maps to do it.  I'll sit there and study where the pic's corners should approximately be, then get the lat/lon from that (clicking directions to or from will yield the lat/lons).

Thank you.

 - Chris  Subject: RE: [UMN_MAPSERVER-USERS] Rasters, TileIndex and Shapefiles - Oh My!  Really Confused
Date: Wed, 26 Sep 2007 13:36:42 -0400
From: ed at topozone.com
To: docterrobert at MSN.COM; MAPSERVER-USERS at LISTS.UMN.EDU



















Chris –

 

Let me suggest you try to get unconfused
just one step at a time!

 

“it uses one .gif
(the big map pic), attaches the big map to the globe via a world file. 
That big map .gif had no georeferencing info attached to it.”

 

That’s a bit of a contradiction.  A
world file is one way of providing georeferencing.  If you’ve got an
image “attached” to the Earth via a world file, you’ve
georeferenced it.

 

MapServer makes maps, not pictures.  One
of the chief differences is that a map has geographic location information
associated with it.  When you ask MapServer to generate a map for you, you need
to tell it the location of the map you want in some coordinate system.  In
order for MapServer to know which of your GIF images to use in making the
output map, it needs to know the geographic location of each of those images.  Otherwise
it couldn’t figure out which ones to use.

 

A TILEINDEX is step two in the process. 
Once you have a set of more than 1 properly georeferenced images that you’d
like to use like a single logical image, you can create a TILEINDEX to do
that.  But you have to completely and correctly make it through step one
first.  Once you get the individual images properly georeferenced, gdaltindex
will just work.

 

So – what do you know about these
images?  Do you really have a world file that correctly describes your big GIF
image?  Do you know exactly how the little images were created from the big
image?  If so, you should be able to figure out how to generate world files for
each individual image.  If not, you’ll need to get that information for
your big image.

 

If you do have that world file and know
how the tiles were created, let us know (you can post the world file in your
reply – it’s just six lines of text).

 

-         
Ed

 

Ed McNierney

TopoZone.com

 

 









From: UMN MapServer
Users List [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] On Behalf Of Christopher Harris

Sent: Wednesday, September 26,
2007 10:02 AM

To: MAPSERVER-USERS at LISTS.UMN.EDU

Subject: [UMN_MAPSERVER-USERS]
Rasters, TileIndex and Shapefiles - Oh My! Really Confused



 

Hi.  I have a map that is
broken up into a bunch of .gif tiles.  I want to display them on a layer
in Mapserver.  I have working version of what I want to accomplish, but it
uses one .gif (the big map pic), attaches the big map to the globe via a world
file.  That big map .gif had no georeferencing info attached to it.



These .gifs have no georeferencing information included or attached as well.



I read Section 4 (and Section 9 too) on the mapserver site page:
http://mapserver.gis.umn.edu/docs/howto/raster_data