[postgis-users] different answers for Transform and cs2cs

Obe, Regina robe.dnd at cityofboston.gov
Fri Oct 31 05:12:25 PDT 2008


Don,
4030 is missing datum information  so I think  when you transform the
datum gets ignored which 
means best proj can guess is that 4030 and 4267 should return same
number since it can't tell if they are the same or different datum

4030 looks like this - "+proj=longlat +ellps=WGS84 +no_defs "

I suspect you should be using 4326 which looks like this
"+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs "

When I use 4326 with your example
select
X( Transform( SetSRID(MakePoint(-86.123456789::double
precision,34.123456789::double
precision),4326),4267 ))::double precision, Y( Transform(
SetSRID(MakePoint(-86.123456789::double
precision,34.123456789::double
precision),4326),4267 ))::double precision;

I get the below which accounting for rounding differences is about the
same
-86.1234814621629;34.1233611276746

Hope that helps,
Regina

-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Don
Sent: Thursday, October 30, 2008 11:11 PM
To: PostGIS Users Discussion
Subject: [postgis-users] different answers for Transform and cs2cs

I have basically the same transformration encoded below in 2 different
ways.  One uses transform the other the program cs2cs.   I am just
trying to convert a latlong to a different datum.  It seems that I am
getting the wrong answer with Transform.

select
X( Transform( SetSRID(MakePoint(-86.123456789::double
precision,34.123456789::double
precision),4030),4267 ))::double precision from al_ent;
       x
---------------
 -86.123456789
 -86.123456789

>cs2cs +proj=latlong +datum=NAD83 +to +proj=latlong +datum=NAD27 -f
%.12f<<EOF
>  -86.123456789 34.123456789
>
> -86.123481462163      34.123361126798 -0.000032913871

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