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20001229: IMGREMAP: MAG= vs RES= (cont.)

>From: Jason Allard <address@hidden>
>Organization: PSU
>Keywords: 200010240345.e9O3jC425238 McIDAS-X IMGREMAP MAG RES

Jason,

re: pixels included in an IMGPROBE box being a function of projection
>Okay, I get this part, I think.  So, if I 'probed' the original image and
>a mercator image (with the same center point) the 'box' worth of data 
>would be slightly different?

Yes, slightly so.

>But. as I mentioned above... the projection I do this from does matter with
>regard to which pixels it will retrieve?

Yes.  You have to remember that the pixels in a remapped image are different
from the original anyway (we have been over this before).

re: what an IMGPROBE box represents
>I guess I understand this, if what I mention above is true.

The best way to convince yourself of all of this is to select a particular
image that has an easily discernable feature and then probe the original
image and a remapped version of the same.  If properly selected, the
feature will let you see the differences in the values returned.  My advice
is to start with a small region with one feature and then expand from
there.  This exercise, while a diversion from your research, will give
you confidence in the results you get.  This will be very important when
it comes time for you to defend your results.

re: No, it isn't, but you can adjust your request to get 80 data within
    an 80 km box.
>Okay, this makes sense... I can use trial and error by changing the number
>of lines and elements until the corners in the mcidas image are at the
>lat/long that I want (find this out by using the Alt E).  This method will
>not allow me to pre-specify each corner, but it does allow me to get close
>to the desired coordinates.

After you do a couple/few cases, you will build up the confidence and
experience that will make succeeding stpes easier and easier.

re: Again, the areal coverage of each pixel is a function of the distance
    it is away from the sub satellite point.  There is no way around this.
>Then I'll have to use the trial and error method I just mentioned.

Sounds good.

re: use of DIST
>This could come in handy to convert the distance from the ULEFT coordinate I
>give mcidas and the other corners... instead of using Alt E on the other
>corners.

Right.  Might as well make use of tools that are there to make your life
easier.

re: ARC/INFO has to deal with projections in the same way as McIDAS, so the
    lessons learned in one package translate to the other.
>Okay

>Basically, with mcidas, I can only specify one coordinate...

Yes, but you can also interrogate the value of each pixel individually.

>it my case, it
>will most likely be the ULEFT corner... then by changing the number of lines
>and elements (and using Alt E), I can get the other corners as close to my
>desired coordinates as possible.

Right.

re: using E command to get Lat,Lon position of a pixel
>Okay, this is part of what I wanted... but I still need to confirm my 
>above assumptions that the pixels extracted from mcidas are dependent upon
>the projection I extract them from.

Yes.  Again, you can get the value of each pixel individually if the
analysis is that crutial (which it shouldn't be since there are so many
other uncertainties in remote sensing).

re: Aside: If you are always dealing with the same location on the surface,
    then the lat,lon corner points will be fixed for whatever size box you
    want.
>This makes me think that my above assumption is incorrect.  Unless you mean
>this in the sense of going between images of the same projection... and if
>my assumption above is true, then your statement won't hold for images with
>different projections.

I was referring to either movement withing the same image, or between
images of the same projection.  Using IMGREMAP you can make different
images have the exact same projection (you have already done this), so
you eliminate one question.  But, always remember that a remapped
image's pixels are not the exact same as the ones from the original
image.  There is no way around this, and the uncertainty is just what
science is all about.

re: PLAX command
>Good point... I'll look over the command.

OK.

re: Since the satellites are geosynchronous, the viewing angle for points
    is not fixed, so you will never get anything exactly.  McIDAS will do
    as good a job as is possible in getting you the values you specify that
    you want.
>Okay, that's all I can ask for.
>
>Once again, thanks,

You are welcome.

Tom