| Re: Minimum curvature surface problem [message #32579] |
Tue, 22 October 2002 10:16  |
Med Bennett
Messages: 109
Registered: April 1997
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Senior Member |
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Med Bennett wrote:
> James Kuyper wrote:
>
>> Med Bennett wrote:
>>>
>>> I'm having a problem using the min_curve_surf function. I am feeding it
>>> data where X and Y are in UTM coordinates (like 650000, 4073500) and Z
>>> ranges from 0.25 to 27,300. The result from min_curve_surf in IDL is a
>>> paraboloid looking surface with a minimum of 2.4E+10 and a max of
>>> 1.2E+15. Needless to say, this is dramatically wrong. I also tried
>>> subtracting off the minimums from the X and Y values to reduce the
>>> number of sig figs, but this does not seem to help. I can compute a
>>> minimum curvature surface with the same data in another software package
>>> (Surfer, Golden Software) and it gives me a reaasonable result. What's
>>> wrong with the IDL implementation, or what am I doing wrong?
>>
>> If you're plotting geo-referenced data covering a significant portion of
>> the Earth, then you should probably be using the /SPHERE keyword. If you
>> are using /SPHERE, then X and Y need to be latitude and longitude in
>> degrees, rather than UTM coordinates.
>>
>> Other than that, I can't think of anything obvious. It might help to
>> post your code.
>
> Hi James,
>
> The area in question is only 4000 meters east-west and 2000 meters
> north-south, so I don't think the earth's curvature is a problem. My code is
> really just the command
>
> mcs = min_curve_surf(cddata,cx,cy,xout=xax,yout=yax)
>
> where xax and yax are just the grid definition. My data looks like
>
> IDL> for i=0,57 do print,cddata[i],cx[i],cy[i]
> 2.50000 654388.42 4074227.3
> 2.50000 653843.10 4074772.3
> 2.50000 653290.98 4074706.9
> 2.50000 653323.82 4075362.3
> 2.50000 653851.11 4074328.6
> 2.50000 653848.19 4073995.6
> 0.250000 653290.04 4074263.0
> 2.50000 653305.74 4073885.9
> 35.6000 652827.10 4074199.2
> 2.50000 652820.14 4074587.5
> 2.50000 652750.34 4074996.8
> 2.50000 652349.49 4074956.4
> 73.1000 652244.41 4074843.5
> 1630.00 652355.23 4074634.6
> 664.000 652379.22 4074291.0
> 1990.00 652375.85 4073980.2
> 2.50000 652046.13 4073952.2
> 3000.00 652031.08 4074295.9
> 151.000 652034.06 4074628.9
> 1230.00 651699.00 4074401.0
> 2.50000 651713.84 4074068.3
> 8830.00 652951.30 4073778.5
> 5.00000 653031.97 4073758.4
> 186.000 651272.11 4074506.6
> 3690.00 651429.43 4074507.6
> 20100.0 651464.52 4074536.9
> 3500.00 651552.10 4074610.7
> 2770.00 651545.20 4074794.1
> 93.7000 651540.86 4075159.0
> 2.50000 650900.82 4074493.5
> 11600.0 652630.78 4073856.0
> 24500.0 652701.20 4073805.4
> 14100.0 652717.04 4073748.5
> 27300.0 652619.43 4073929.3
> 251.000 651228.38 4074786.7
> 11200.0 651343.95 4074680.8
> 2.50000 652661.85 4073649.9
> 9.10000 652528.42 4073788.9
> 2.50000 652527.30 4073773.8
> 2350.00 652648.33 4073675.5
> 2080.00 652648.17 4073683.7
> 12.3000 652647.31 4073705.1
> 2.50000 652704.45 4073637.8
> 2.50000 652706.39 4073645.0
> 2.50000 652706.39 4073645.0
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ bad!
>
> 2.50000 652796.01 4073604.5
> 2.50000 652978.58 4073553.7
> 3600.00 652700.44 4073719.5
> 10300.0 652772.18 4073722.6
> 4900.00 653065.91 4073832.9
> 0.600000 653198.66 4073806.5
> 13900.0 651645.66 4074401.0
> 5.00000 651053.48 4075268.2
> 5.00000 650699.44 4075252.1
> 5.00000 650653.14 4074709.0
> 670.000 651331.96 4075131.0
> 1630.00 651127.30 4074695.9
> 20.0000 650907.27 4075118.6
>
> I'd be happy to mail a couple of gif's illustrating the results if you're
> interested. Thanks, Med
How embarassing - it appears that the one duplicate X,Y data point I had in my
arrays was causing min_curve_surf to blow up. Not the first time I've tripped
up by @#$&* duplicates! These are analytical chemistry data and they often have
duplicate analyses from the same location. sorry sorry sorry - M
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