[Mapserver-users] Projection Help

Wed Apr 7 19:54:22 EDT 2004

Paul,

The moment you crop a photo, whatever spatial referencing information (where
it sits in geographic space) you had becomes invalid, because that
information is usually based on the absolute location of a corner of the
image, plus information on the geographic size of a pixel. You are far
better of leaving your imagery intact (especially when you're debugging).

Pyramids in ArcMap make it faster, but I don't like them because they
decrease graphic quality. It is just an indexing method to make it display
faster.

It says it's missing "spatial reference information" because it doesn't know
where your image should sit in real-time space (even if you had a .jpw or
.wld file with information on its location, it would be invalid after you
cropped it).

You said through georeferencing, you expand it to the right proportions. Do
you mean location as well? If you got your image to sit in the rigth spot,
based on other information you had (roads, or whatever you used), then
you're better off creating an ortho-image: In the 'georeferencing' toolbar,
select 'rectify'. This button only activates if you changed the location of
your image. It will output a TIFF file with a TFW file. These files will be
georeferenced, and sit in the right spot. Theoretically, mapserver can
display these.

The reason that what you did isn't working is probably that ArcMap saves
georeferencing information (shifts, scale change, etc.) to a .AUX file. This
information is not read by mapserver, so it will only be in the right spot
when opened in ArcMap. That is why you have to output a TIFF, because then
it will simply re-create the image with your modifications built into it,
and a correct .tfw file.

But like I said, normally you're better off to stick with your original
image, find out its extents, and maybe write a jpw file for it. The more you
resample, the more quality you lose.

Regards,

Jacob

-----Original Message-----
From: Paul VanDyke [mailto:pvandyke at kib.co.kodiak.ak.us] 
Sent: Thursday, 8 April 2004 06:16
To: Frank Warmerdam
Cc: mapserver-users at lists.gis.umn.edu
Subject: RE: [Mapserver-users] Projection Help

I'm sorry for not being too specific, but I didn't know what information was
necessary.  Thank you for the questions.

Here's what I'm doing:

I acquired a .jpg satellite picture of Alaska that was 5202x4002 pixels. I
cropped it to 1800x1162 pixels (to include only the relevant parts) and
saved it as a 24-bit uncompress RGB .tif file

When I add it to ArcMap, it prompts me to build pyramids, which I say YES to
and then I get a message that says, "One or more layers is missing spacial
reference information. Data from those layers cannot be projected."

The raster shows up a just a spec on the map, but thru the georeferencing
process, I expand it to the proper proportions and then output a recitfied
image.  I realize that this image is going to be very grainy when zoomed in,
but it's just a birds eye view (a very high
bird/satellite) of our island.

The rectified .tif does not have a coordinate system defined for it yet as
checked with the LISTGEO command.

Then I assign it a projection from within ArcCatalog by right-clicking and
selecting properties; choosing the "Spacial Reference" tab and clicking
Edit; I then choose Import and select one of the shape files that is on the
map and import it's coordinate sytem, which happens to be
NAD_1927_StatePlane_Alaska_5_FIPS_5005.

When I look at my MapServer output, the raster is plotted south of the
shapefile by a big stretch. I originally said 100 miles but I think it's
probably more like 700 miles.  Changing the projection in my .map file from
init=epsg:26705 to init=epsg:26735 make the map disappear entirely. One of
the rasters that work is of type 26705, but the shapefile that I'm working
with is 26735.

Please feel free to comment on my proceedures.  Maybe I'm missing a step,
but it all looks good in ArcMap...

Thanks,

Paul

-----Original Message-----
From: Frank Warmerdam [mailto:warmerdam at pobox.com] 
Sent: Wednesday, April 07, 2004 9:29 AM
To: Paul VanDyke
Cc: mapserver-users at lists.gis.umn.edu
Subject: Re: [Mapserver-users] Projection Help

Paul VanDyke wrote:
> Most of my raster images are working great and I am very thankful to
> those who helped me.  However, I am having problems with a few of my 
> rasters and I'm scratching my head...
> 
> I am adding them as a layer to my ArcMap project, doing the
> georeferencing, then exporting them out.  I've gotten a few to work, 
> but others haven't.  The last one I did showed up on my MapServer map 
> about 100 miles south of where it should have been.  I've tried 
> playing with the projection in my .map file and I've tried defining 
> the spacial information in ArcCatalog.  I realize that I don't have 
> the knowledge/background/training to do the job that I'm doing, and so

> I am asking for help from this community.  If you can provide me with
> any links/websites with further information, I'd be very appreciative.

> If you can tell me why my raster displays 100 miles south (roughly) of

> where it's supposed to, I'd be indebted.
> 
> The map in question is Map 9 at http://209.165.152.73 and you'll have
> to zoom out to the south to see what I'm talking about.

Paul,

This isn't much for us to go on.

Where did you get the data?  Did it come with any coordinate system
information or other metadata that might be helpful?  Can you go back to the
source to get such information?  Does it display properly in ArcMap? What
projection definition are you using now?  Why?  Do you have other layers
that are working properly?  What coordinate system are you using for them?

A 100 mile error could be the result of a number of things.  Perhaps you are
using the wrong state plane zone, or are missing false easting/northings.
What it is not is a datum/ellipsoid error since those errors would be tiny
by comparison.

Best regards,

-- 
---------------------------------------+--------------------------------
---------------------------------------+------
I set the clouds in motion - turn up   | Frank Warmerdam,
warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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