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| GeoCommunity Mailing List |
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| Subject: | Re: [gislist] 'transpose' |
| Date: |
07/26/2006 06:45:00 PM |
| From: |
Bryan Keith |
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John,
I make transformations like this frequently to move between a real
coordinate system and finite difference model space for a number of
modeling projects. I'm not sure what the name of the procedure is or if
there is one (coordinate rotation?). For my work often it's just a
simple rotation and x offset and y offset. Given a rotation, x and y
offset and x and y scale, you can transform a set of coordinates from
one system to another.
Here's a simple example that I found quickly that works for me for one
project (there's no scaling and it works for whatever quadrant my
rotation's in):
dXNew = (dX - dXOrigin) * Cos(dAngle) + (dY - dYOrigin) * Sin(dAngle)
dYNew = (dY - dYOrigin) * Cos(dAngle) - (dX - dXOrigin) * Sin(dAngle)
Maybe that helps.
Bryan
Bryan Keith
GIS Specialist
Geomega, Inc.
Boulder, CO, USA
John Daues wrote:
> I am trying to remember a term used in GIS that I heard used by a GIS
> person. It has similar meaning to the word 'transposed'. It is used to
> describe this process:
>
> Suppose I have a rectangular transect in a landscape that runs something
> other then straight east-west or north-south, ie, at some diagonal. The
> illustration here shows this where 0 is 'not transect' and non-zero is
> the transect, with each number representing (let's say) a vegetation type:
>
> 000000000
> 000000132
> 000003440
> 000044400
> 000443000
> 004330000
> 033300000
>
>
> This GIS person cuts/rotates this transect such that you end up with
> data that looks like this:
>
> 344431
> 334443
> 333442
>
> The purpose of this is that the 2nd data set is much easier to work
> with, computationally, than the first.
>
> Anybody know the word I am looking for?
>
> Thanks!
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