[Geotiff] Ignored Tie Points in ERDAS?

[Co-op DA]

Hello,

I'm new to geotiffs, and I have been spending the past few weeks getting the
information together to write metadata files, to be used with geotifcp. I
have three images that I am trying to georeference, and I have had success
with the two smaller ones. All of the images are Polar Stereographic, but
have different central meridians. 

The image that I am having trouble with depicts most of North America. I am
very sure that I have all of the keys right. I also have collected a lot of
tie points that I am very confident in, because many of them lie on an
intersection of the latitude/longitude grid in the image. However, there
seems to be some problem with the tying. If I specify more than 3 tie
points, the image doesn't seem to respond much to further points. 5 point
and 66 points look virtually the same, and both are distorted incorrectly.
It isn't a translation issue - the image is just not opening in quite the
right shape, or the right place. 

I've been trying different sets of three points, and the resulting
distortions vary widely. As I understand it, if all the projection
information is complete and you provide at the very least two correct tie
points, the image should be successfully referenced. The fact that the
choice of points dramatically changes the appearance of the geotiff suggests
to me that something is badly awry. Here's my metadata file that I'm working
with:

Geotiff_Information:
   Version: 1
   Key_Revision: 1.0
   Tagged_Information:
       ModelTiepointTag (7,6):
       2          2           0        -3415328.4652632         
-59734.0339616709     0    
       2          337        0        -3216318.85713759        
-5885451.94765147     0    
       571       337        0        5396145.23162201         
-4185980.99679257     0    
       571       2           0        3355077.60552792         
1277959.98036367      0
       291       70         0         303000.290631328         
-789342.743722715     0
       132       196        0        -1553107.57503345        
-2801880.23443414     0
       382       197        0        1883394.10004617         
-2166597.07103956     0
      End_Of_Tags.
   Keyed_Information:
      GTModelTypeGeoKey (Short,1): ModelTypeProjected
      GTRasterTypeGeoKey (Short,1): RasterPixelIsArea
      GTCitationGeoKey (Ascii,31): "UDF1 North Polar Stereographic"
      GeographicTypeGeoKey (Short,1): User-Defined
      GeogCitationGeoKey (Ascii,29): "Projection based on a sphere"
      GeogGeodeticDatumGeoKey (Short,1): User-Defined
      GeogPrimeMeridianLongGeoKey (Double,1): 0.0
      GeogLinearUnitsGeoKey (Short,1): Linear_Meter
      GeogAngularUnitsGeoKey (Short,1): Angular_Degree
      GeogEllipsoidGeoKey (Short,1): User-Defined
      GeogSemiMajorAxisGeoKey (Double,1): 6371000
      GeogSemiMinorAxisGeoKey (Double,1): 6371000
      ProjectedCSTypeGeoKey (Short,1): User-Defined
      PCSCitationGeoKey (Ascii,31): "UDF1 North Polar Stereographic"
      ProjectionGeoKey (Short,1): User-Defined
      ProjCoordTransGeoKey (Short,1): CT_PolarStereographic
      ProjLinearUnitsGeoKey (Short,1): Linear_Meter
      ProjNatOriginLongGeoKey (Double,1): -111.0
      ProjNatOriginLatGeoKey (Double,1): 60.0
      ProjFalseEastingGeoKey (Double,1): 0
      ProjFalseNorthingGeoKey (Double,1): 0
      ProjScaleAtNatOriginGeoKey (Double,1): 1
      ProjStraightVertPoleLongGeoKey (Double,1): -111.0
      End_Of_Keys.
   End_of_Geotiff.


I'd appreciate any suggestions or guidance.

Thanks,

Colleen
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