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
Solved! Go to Solution.
Why don't you just download a georeferenced version? Search for a Dataset - Data.gov
Why don't you just download a georeferenced version? Search for a Dataset - Data.gov
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.
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.