Hello,

I am in the process of decoding radial nexrad images (product code 19
currently) and was wondering if I could get some clarifcation on a couple
of items.

For reference, I'm looking at the Interface Control Document for the RPG
to Class 1 user.

First of all, I can decode the data with no problem, so that much is good
to go. However, I am a bit confused as to how the I and J sweep center
point and scale factor come into play. I'm noticing on the particular
data set that I'm decoding that the I, J center point is (256, 280) and
the scale factor is 0.999. I used figure 3-10 (sheets 1 & 2) to use as a
reference for these values.

Does the I, J coordinate correspond to the center of the radar? If so, I
assume that this would have to further correspond to the lat/lon of the
radar as given in the Graphic Product Message. Assume both of these
assumptions are correct, I'm a little confused about why the I, J
coordinate is even needed. Can you help me out here?

Regarding the scale value, the number of bins in the scan is 230, so there
seems to be some precision issues with the scale factor (i.e. should be
1.000) according to the equation presented in figure 3-10 of the WSR-88D
ROC. It states (230 / #bins == scale factor).

Does anyone have experience using this? I'd be most greatful for any help
on it.

Thanks,
Brian