# About free-air anomaly data & RTP module

**URL:** <https://forum.generic-mapping-tools.org/t/about-free-air-anomaly-data-rtp-module/3691>\
**Category:** Q&A\
**Created:** [February 19, 2023, 4:43am UTC](https://forum.generic-mapping-tools.org/t/about-free-air-anomaly-data-rtp-module/3691 "2023-02-19T04:43:19Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![prince-Ha](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/prince-ha/32/2754_2.png) [@prince-Ha](https://forum.generic-mapping-tools.org/u/prince-Ha)\
**Post date:** [February 19, 2023, 4:43am UTC](https://forum.generic-mapping-tools.org/t/about-free-air-anomaly-data-rtp-module/3691/1 "2023-02-19T04:43:19Z")

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Hello, first of all, thank you for making a good program.  
I would like to ask you a few questions while using pygmt.

1. 

gmt provides free-air anomaly data from the link below. I wonder if this data is free-air random or gravity disturbance. When I asked other people, I heard it was free-air anomaly, but I would like to hear an accurate answer.

> **[IGPP Global Earth Free-Air Anomaly — Remote Datasets documentation](https://www.generic-mapping-tools.org/remote-datasets/earth-faa.html)**

1. 

> **[grdredpol — GMT 6.4.0 documentation](https://docs.generic-mapping-tools.org/latest/supplements/potential/grdredpol.html)**

There is a grdredpol code among gmt modules, can I use it in pygmt? I’m asking because I need to apply regional area rtp now.

thank you

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**Author:** ![maxrjones](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/maxrjones/32/2698_2.png) [@maxrjones](https://forum.generic-mapping-tools.org/u/maxrjones)\
**Post date:** [February 21, 2023, 5:41pm UTC](https://forum.generic-mapping-tools.org/t/about-free-air-anomaly-data-rtp-module/3691/2 "2023-02-21T17:41:36Z")

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Have you reviewed the [two citations for that data product](https://www.generic-mapping-tools.org/remote-datasets/earth-faa.html#data-references)? As the GMT team did not create that dataset, we would similarly be a second-hand source for clarifying questions.

grdrelpol is currently not wrapped in PyGMT. You could either open a feature request (either waiting for a contribution or working to add the feature) or attend to use the clib module in PyGMT (e.g., [Calling grdfft with pygmt](https://flint.soest.hawaii.edu/t/calling-grdfft-with-pygmt/1926)).

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**Author:** ![prince-Ha](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/prince-ha/32/2754_2.png) [@prince-Ha](https://forum.generic-mapping-tools.org/u/prince-Ha)\
**Post date:** [February 24, 2023, 8:49am UTC](https://forum.generic-mapping-tools.org/t/about-free-air-anomaly-data-rtp-module/3691/3 "2023-02-24T08:49:49Z")

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I thought the GMT developers created a free-air anomaly

I’m sorry. @maxrjones

I’ll try the module.

Thank you.

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**Author:** ![pwessel](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/pwessel/32/30_2.png) [@pwessel](https://forum.generic-mapping-tools.org/u/pwessel)\
**Post date:** [February 24, 2023, 9:19am UTC](https://forum.generic-mapping-tools.org/t/about-free-air-anomaly-data-rtp-module/3691/4 "2023-02-24T09:19:11Z")

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Our involvement is just the tiling, downsampling, JP2000 packing, and delivery for all resolution versions, but the original sys comes from unmodified Scripps or elsewhere as the docs imply.

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**Author:** ![prince-Ha](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/prince-ha/32/2754_2.png) [@prince-Ha](https://forum.generic-mapping-tools.org/u/prince-Ha)\
**Post date:** [February 28, 2023, 2:58pm UTC](https://forum.generic-mapping-tools.org/t/about-free-air-anomaly-data-rtp-module/3691/5 "2023-02-28T14:58:14Z")

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thank you

I understand !!!