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## [task #15669] Calculating forward coefficients of TPV to SIP

 From: Sachin Kumar Singh Subject: [task #15669] Calculating forward coefficients of TPV to SIP Date: Tue, 2 Jun 2020 17:23:13 -0400 (EDT) User-agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:75.0) Gecko/20100101 Firefox/75.0

```Follow-up Comment #1, task #15669 (project gnuastro):

Now, features are implemented to do the tpv->sip translation for forward
coefficients. They are pushed here
<https://gitlab.com/sachinkumarsingh092/gnuastro-test-files>. The final
results in the headers of the python implementation(using sip_tpv module in
astropy which is done here
<https://gitlab.com/sachinkumarsingh092/gnuastro-test-files/-/blob/master/scripts/tpv2sip.py>)
and the test GnuAstro library are shown below:

Using sip_tpv module in astropy:

A_0_0   =  -0.5947048847413352

A_0_1   = 0.000511373196373184

A_0_2   = 9.71733789710970E-07

A_0_3   = -6.2376422946773E-10

A_1_0   = 0.000870132842249571

A_1_1   = 5.60499034638399E-07

A_1_2   = -2.5505398795854E-10

A_2_0   = 1.01770599638340E-07

A_2_1   = -2.1900816534747E-10

A_3_0   = -4.3245647824626E-10

Using test GnuAstro library:

A_0_0   =  -5.947048847413E-01 / SIP distortion coefficient:

A_0_1   =   5.113731963732E-04 / SIP distortion coefficient: y

A_0_2   =   9.717337897110E-07 / SIP distortion coefficient: yy

A_0_3   =  -6.237642294677E-10 / SIP distortion coefficient: yyy

A_1_0   =   8.701328422496E-04 / SIP distortion coefficient: x

A_1_1   =   5.604990346384E-07 / SIP distortion coefficient: xy

A_1_2   =  -2.550539879585E-10 / SIP distortion coefficient: xyy

A_2_0   =   1.017705996383E-07 / SIP distortion coefficient: xx

A_2_1   =  -2.190081653475E-10 / SIP distortion coefficient: xxy

A_3_0   =  -4.324564782463E-10 / SIP distortion coefficient: xxx

So this task can now be closed:-)

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