Congrats! Simpeg is amazing! I just started using Simpeg. I have a question about Gravity tutorial Forward Simulation of Gravity Anomaly Data on a Tensor Mesh (Forward Simulation of Gravity Anomaly Data on a Tensor Mesh — SimPEG 0.14.3 documentation).
Why in “Simulation: Gravity Anomaly Data on Tensor Mesh”, in the example, have negative mgal anomalies related to sphere positive density body 0.2 g/cc and positive mgal anomalies related to block negative density -0.2 g/cc. It wouldn´t be the opposite??
Thanks!
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Hi @Marcelo,
SimPEG is consistent with having a Z-up positive convention for all methods (the Z-axis points up).
Example: A body with a positive density-contrast produces more pull, consequently its vector gravity anomaly is pointing down. Thus it produces a negative anomaly in that convention (which is, indeed, the reverse of the usual convention for gravity).
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New SimPEG user who had the same question. I figured it was like this and found this question and answer helpful.
Can I suggest that in the grav forward simulation tutorial the comment text be updated from “SimPEG uses right handed coordinate where Z is positive upward. This causes gravity signals look “inconsistent” with density values in visualization.” be updated to be more clear on this convention.
Thanks for all your great work and for having this discussion board open for new users. It’s very helpful!