[gradsusr] Help: How to interpolate the shaded area where there are only a few points (lets say 3)?

[얍준후이]

Hi all,
 
I am trying to figure out how to interpolate the shaded area to make it looks more presentable to see.
 
The shade level is represented by julian date.
 
I only have 3 input points from the input as per below:
 
StationID    Longitude    Latitude        JulianDay
100            36.573          128.707        249
121            35.105          129.032        262 
122            36.573          128.040        265 
 
As you can see station 121 and station 122 are near to each other, whereas station 100 is further apart.
 
By making the JulianDay 249 as the min. shaded level and JulianDay 265 as the max. shaded level. It gives me a non-interpolating area. (refer to the attachment)
 
Any idea on how to fix this?
 
Regards,
JH
 
 
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