ArcGIS 10.2 - Trouble to georeferenced an image?

[VincentLaunstorfer]

Hi,

I got a shaded-relief image for North America from the USGS but it is not georeferenced.

Attached are the characteristics of the image in ArcCatalog, and the extent was filled-in by the .tfw file I made, as attached.

Looking at the image, I guessed the upper-left corner was long -130 and lat +60. Still according to the image, I found the upper-right corner long -50 and lat +60 while bottom-left long -130 and lat +15

With 9600 columns, the cell size would be: (130-50) / 9600 = 0.008333333°, which is 30''. Looks good

And with 7240 rows, the cell size would be: (60-15) / 7240 = 0.006215469°, whi ch is roughly 22''. Not as good.

Even with a .tfw with these values do not update the Cell Size in the image in ArcCatalog. Why? Usually, it does...

Also, would it be possible to have rectangular pixel? I guess why not...

Does the number of bands, which are 3, change anything in georeferencing the image? How could I convert the image from 3 bands to 1 bamd only?

Thanks for your help

[SepheFox · Accepted solution]

Why don't you just download a georeferenced version? Search for a Dataset - Data.gov

[DarrenWiens2]

Also, would it be possible to have rectangular pixel? I guess why not...

Your pixels must be stored as squares, however you can trick ArcMap into displaying rectangular pixels on-the-fly by changing the data frame projection to one which introduces significant distortion. Of course, this doesn't help your case, but you should abandon the plan to specify rectangular pixels.

[VincentLaunstorfer]

Thanks

For no reason, my North American image was tricky to georeference and the Data.gov portal has plenty of imagery (ans WMS) for download. Though, I haven't find a nice North American grey relief-shaded yet... Just for conterminous United States so far. Need to look more into the images available.