[GRASSLIST:1622] Re: More projection problems...

[mberglund]

On Fri, 16 Mar 2001, Morten Hulden wrote:

> > After trying what Morten suggested, (shifting the false easting) yes it is
> > closer, but still  about 8000 feet off.
> 
> Yes, you can keep changing the parameters until you get the points to
> match. But one test point is not enough if you want to try to match the
> maps by altering the parameters. You need many points with known
> co-ordinates all over the map. For this kind of matching i.rectify maybe
> is a better tool. I just mentioned reducing the false easting as one way
> of adjusting the Albers map.
> 
> The main question still is: Are you sure that the upper left corner
> co-ordinates of the two locations really should coinside. Can you locate a
> geographic feature (city, lake, whatever) for which you know the
> co-ordinates, and which is present on both maps? If you can, then use that
> as a testpoint. 
This I kmay be able to do. I will hunt down some points and get the
coordinates.

> What I meant was: Your STP location is in 1-foot resolution (1x1 foot
> cells), the Albers map is in 1-meter resolution. You cannot expect to get
> more detail than what is available in the Albers map. You might as well
> reduce the resolution of the STP location temporarily to about 3x3 feet
> cell size before importing the Albers map (by defining a region within the
> STP location, with the same borders as the default region but with a
> different resolution). The projection will be faster and the imported map
> will become smaller in size, but the quality will still be the same.
Cool, I get it know.

> Also, I wanted raise the question whether your Albers map really _is_ in
> 1-meter resolution. Or did you just create the location that way? I
> believe it's unusual to have Albers in such high resolution, but of course
> it is possible.
This raises an interesting question. The image is a 1-meter doq. that is
to say that the image was taken with 1 meter accuracy (so I assume, and if
I am wrong folks, please speak up.)

So, I don't know, from that do we know that the map is really 1 sqr. meter
resolution. I guess I just assumed so, but as I told Bruce, I am not a
real map guy, more of a programmer guy. We'll see if my map guy wings
sprout and fourish or wither and fall off!

> Grass can do it better. It's only a matter of getting the data parameters
> right.
With your help, I don't see how I can go wrong! :)

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It is well structured, always growing, and has passed the test of time.