[UW-GIS-L] scale problem?

[Keven Bennett]

    It's hard for me to tell, but those look like UTM (meters) coordinates
and I've never seen much data in NAD 83 in UTM.  Likely from the fact you
got it from DRGs it's likely to be UTM Zone 10 NAD27 in meters.
    Your other data is in geographic DD.
    I may be wrong, but I think that ArcGIS, though it can do 'on the fly'
stuff, cant correctly rescale one to the other across these two frames of
reference.

    Try going into arctools, and define the projection of your points as
geographic decimal degreees using North American Datum of 1927 (the NAD27
referred to earlier).
    Then use the projection tools to reproject it into UTM Zone 10 NAD27
with horizontal units as meters.  I think that there is a good chance it
will match up.

    Keven Bennett
    ONRC GIS

----- Original Message ----- 
From: "Sacha Vignieri" <sachav at u.washington.edu>
To: <uw-gis-l at u.washington.edu>
Sent: Sunday, November 23, 2003 7:05 PM
Subject: [UW-GIS-L] scale problem?


> Hello again,
> Thanks to everyone who provided advice on this problem earlier, it was
> extremely helpful! I have come closer to solving the problem, but am
> still stuck. I was able to get some assistance from more experienced
> users and together we were able to ensure that we were correctly
> attempting to place both my lat long points and the TIFF map (changed
> into a raster grid) in the same projection. We even reprojected both
> datasets and in doing so were able to see the points plotted on the same
> screen as the map (however I am unconvinced that the map was changed).
> This made it clear that there is a scale issue occuring. The points and
> map are off by several orders of magnitude. In the metadata preview, the
> boundings for the map are
> West: -444153.292651
> East:-442348.673352
> North: 172351.152340
> South: 170998.773464
>
> Whereas those of the points are
> West: -123.538300
> East:-122.537003
> North: 47.480598
> South: 47.400002
>
> Clearly, the point boundaries are determined from the lat long values.
> Perhaps the map is in meters? I have tried to reproject the map,
> unsuccessfully. I have also tried to reproject the points into UTM (and
> many other projections) with no change in scale. I am not sure how to
> re-define one or the other so that they will overlap. When I overlayed
> the points onto a map of the US provided with the ArcGIS software, they
> maintained their considerably larger scale. These points were collected
> in a river drainage that spans, at most, 30 miles. When overlayed onto
> the Washington portion of the US map, they appeared spread out across
> the entire Olympic Peninsula.
>
> Hopefully, this will be my last call for help.
> Thanks again for your advice and time!
>
> Sacha Vignieri
> Department of Biology
> University of Washington
> sachav at u.washington.edu
>
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