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Projection roundtip losing too much precision for NAD27 at -128.0 longitude #47
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I tried to replicate this on the command line with cs2cs:
The round trip result was I used pyproj.Geod for the distance calculation and got: 6.0880917533296244e-09 meters. Close enough to your last result. This bug could be problematic. |
That is (kind of) good news. What else can I do to figure out what is causing this? |
Sorry, I didn't replicated your example fully. Here is the version with the error. Using -128.0 longitude.
And the distance calculation: >>> from pyproj import Geod
>>> wgs84_geod = Geod(ellps='WGS84')
>>> angle1, angle2, distance = wgs84_geod.inv(-128.0, 50.98, -128.00005191895048, 50.98006355013496)
>>> distance
7.954670001528683 That is similar to your results, about 8 meters off. Base on that I don't think pyproj is at fault, it is just using what the underlying PROJ.4 C library is giving it. Please report this issue to proj.4. |
Sorry. From my local tests I already noticed that some values around -128.0 don't trigger the issue.
|
This seems to be an issue of OSGeo/proj.4. Reported here. Closing. |
I'm trying to test roundtrip (roundtrip is p1->p2->p1) stability in my projections and found a curious case (a bug?) when trying to convert from WGS84 to NAD27 and back.
We can see the values here:
And they are almost 8 meters apart:
I have tested several positions and I only seem to have problems with longitude at
-128.0
and latitudes between50.98
and76.98
.For example:
Which seems to be just fine!
I also tested this with ArcGis API and it seems to work fine.
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