Bug #828

Clarification for project

Added by Mark almost 3 years ago. Updated over 2 years ago.

Status:FeedbackStart date:2015-12-04
Priority:NormalDue date:
Assignee:Paul% Done:


Target version:-
Affected version:5.1.x Platform:Mac OS X


I am reporting back on something that stumped me in using gmt project. I noticed this issue when using the -G generate mode. The model uses -C to define the center of the projection, which is defined where p,q = 0,0. However, I find that when I specify a length for small circle, using -L and -Q, the length is defined as if the center is at the oblique equator. Of course, -G does not work for a small circle unless the colatitude is appended to the -G option.

I include an example below to demonstrate this issue. My opinion is that it would be better for the user to follow the concepts associated with a map projection. As such, I view the oblique projection provided by project to be defined relative to a central oblique meridian and a central oblique parallel. My intuition suggests that -C defines the lon, lat point where those two features cross. Alternatively, maybe -C is meant to mean the start of a path, in which case, it is no longer relevant to the center or origin of the projection.

Best, Mark

exampleGenerateSmallCircle.sh Magnifier - example showing problem (1.92 KB) Mark, 2015-12-04 05:26


#1 Updated by Paul over 2 years ago

  • Status changed from New to Feedback
  • Assignee set to Paul

I fixed issue #837 which has a bearing on your issue here. Could you please svn update and see if this problem has been fixed or possibly changed? If so please update the issue.

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