[postgis-users] Bug or Problem with st_transform

[Paul Ramsey]

Those are the correct answers...

On Tue, May 18, 2010 at 10:15 AM, Charles Galpin <cgalpin at lhsw.com> wrote:
> Steve, I get the same results on 1.4 and 1.5 (but they differ from yours)
>
> On 1.4
>
> "PostgreSQL 8.4.2, compiled by Visual C++ build 1400, 32-bit"
> "POSTGIS="1.4.1" GEOS="3.2.0-CAPI-1.6.0" PROJ="Rel. 4.6.1, 21 August 2008" USE_STATS"
>
> "LINESTRING(0 0,4030 0,4030 4030,0 4030)";
> "LINESTRING(0 0,2.46766330028192e-013 4030,-4030 4030,-4030 2.46766330028192e-013)";
> "LINESTRING(0 0,2.21673965870407e-018 0.0362021035411944,-0.0362021059500167 0.0362021035411944,-0.0362021059500167 0)";
> "LINESTRING(-71.26162 42.30028,-71.26162 42.3364821035412,-71.29782210595 42.3364821035412,-71.29782210595 42.30028)"
>
> On 1.5
>
> "PostgreSQL 8.4.2 on x86_64-redhat-linux-gnu, compiled by GCC gcc (GCC) 4.1.2 20071124 (Red Hat 4.1.2-42), 64-bit"
> "POSTGIS="1.5.1" GEOS="3.2.0-CAPI-1.6.0" PROJ="Rel. 4.7.1, 23 September 2009" LIBXML="2.6.26" USE_STATS"
>
> "LINESTRING(0 0,4030 0,4030 4030,0 4030)";
> "LINESTRING(0 0,2.46766330028192e-13 4030,-4030 4030,-4030 2.46766330028192e-13)";
> "LINESTRING(0 0,2.21673965870407e-18 0.0362021035411944,-0.0362021059500167 0.0362021035411944,-0.0362021059500167 0)";
> "LINESTRING(-71.26162 42.30028,-71.26162 42.3364821035412,-71.29782210595 42.3364821035412,-71.29782210595 42.30028)"
>
> hth,
> charles
>
> On May 18, 2010, at 11:39 AM, Stephen Woodbridge wrote:
>
>> Mark Cave-Ayland wrote:
>>> Stephen Woodbridge wrote:
>>>> Hi guys,
>>>>
>>>> This is looking like it might be a bug on version "POSTGIS="1.3.3" GEOS="3.0.0-CAPI-1.4.1" PROJ="Rel. 4.6.0, 21 Dec 2007" USE_STATS" which I know is ancient, but upgrading is not trivial.
>>>>
>>>> What I am trying to do is construct a shape in 900913 in meters and then rotate, transform it to 4326 and translate it to a location.
>>>>
>>>> The problem is the transform does not look correct. To just rough out the math, 4030 meters should be about 0.036202 degrees based on
>>>> 4030/40075016*360 = 0.036202 but st_transform is giving back numbers like -5.67596869587729e-09
>>>>
>>>> Is this a known problem on this version?
>>>> Is my logic faulty?
>>>> Is there a better way to do this?
>>>>
>>>> Thanks,
>>>>  -Steve
>>> Hi Steve,
>>> The first thing I would suggest is that you run the same query on a spare fresh 1.4/1.5 installation and see what happens. The transformation code had a good tidy up and some logic corrections within that timeframe, including better reporting of error messages.
>>
>> Hi Mark, et al,
>>
>> 1) Can someone run this query 1.4 and report back the results:
>>
>> SELECT astext(st_linefromtext('LINESTRING(0 0,4030 0,4030 4030,0 4030)', 900913)),
>>       astext(st_rotate(st_linefromtext('LINESTRING(0 0,4030 0,4030 4030,0 4030)', 900913), radians(90))),
>>       astext(st_transform(st_rotate(st_linefromtext('LINESTRING(0 0,4030 0,4030 4030,0 4030)', 900913), radians(90)), 4326)),
>>
>> astext(st_translate(st_transform(st_rotate(st_linefromtext('LINESTRING(0 0,4030 0,4030 4030,0 4030)', 900913), radians(90)), 4326),-71.26162, 42.30028));
>>
>> It assumes that you have 900913 loaded in your spatial_ref_sys table.
>>
>> 2) Does anyone know where I can get postgis 1.4 for debian lenny. I can get postgresql 8.4 from from backports.org, but they do not have postgis there. Ideally, at package like postgresql-8.3-postgis based on 1.4 would be simplest, but I'm willing to take a couple of days to dump and reload all my databases to upgrade to postgresql 8.4 also.
>>
>> Thanks,
>> -Steve
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