[Proj] Problems with /Op option used to compile proj in Microsoft Visual Studio
mauceri at actgate.com
Wed Mar 14 12:32:21 EST 2012
I've been struggling since a few days to understand a very odd behavior
I have 2 versions of proj libraries and utils, one compiled with
Microsoft Visual C++ 2008 (Express Edition) and another one compiled
with Microsoft Visual C++ 2003.
Analyzing some strange results in our processes, I found out that
executing some transformations using the two proj libraries return two
(very) different results.
Here is an example of a transformation that is giving me problems using
the cs2cs utility.
cs2cs -f "%.5f" +proj=tpeqd +a=2440e3 +b=2440e3 +lat_1=-22.960070000
+lon_1=65.546300000 +lat_2=-22.959730000 +lon_2=65.546160000 +no_defs
+to +proj=longlat +a=2440e3 +b=2440e3 +lon_0=0 +no_defs
On the cs2cs compiled with Microsoft Visual C++ 2008 that transformation
returns a meaningful result
65.56780 -23.01227 0.00000
while in the version compiled with Microsoft Visual C++ 2003, it returns
* * 0.00000
The same result happens with other (few) sets of coordinates.
Looking at the error returned in the latter case, the pj_transform exits
-19: acos/asin: |arg| >1.+1e-14
The error happens in the aacos function: in the first case
0.999999999999996 is passed to the function while in the other case the
number passed to the aacos is 1.000000000000012.
Now, looking (by chance) at the compilation options of the proj, I
noticed that between the options passed to the cl compiler there is the
consistency floating point option " /Op". As stated in the "Microsoft
Visual Floating-Point Optimization"
"The consistency model can seriously reduce efficiency while
simultaneously providing no guarantee of increased accuracy. To serious
numerical programmers, this doesn't seem like a very good tradeoff and
is the primary reason that the model is not generally well received."
Disabling that option, the result returned in the version of proj
compiled with Microsoft Visual C++ 2003 is more consistent.
Is there any reason why the /Op option is used to compile the proj?
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