[postgis-users] Need Help with Transform

Thu Sep 11 12:07:47 PDT 2008

RH,

I'm not aware of an easy way to tell if its in range (I think you can
from the proj4text lon a b blah blah blah args) defined in
spatial_ref_sys, but I'm not that technically savvy.

  If you get something like all the same long lat when you project back
to 4326 (WGS 84), or you get weird numbers like 135, 90 etc. then its
probably wrong.

Given that all your below seem to project to below - I would say you are
wrong
POINT(-115.583333333333 90)

First of all when I look in spatial ref

SELECT srtext from spatial_ref_sys where srid = 32107 

I get the below
"PROJCS["NAD83 / Nevada
East",GEOGCS["NAD83",DATUM["North_American_Datum_1983",SPHEROID["GRS
1980",6378137,298.257222101,AUTHORITY["EPSG","7019"]],AUTHORITY["EPSG","
6269"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0
1745329251994328,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4269"]],PRO
JECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",34.75],PAR
AMETER["central_meridian",-115.5833333333333],PARAMETER["scale_factor",0
.9999],PARAMETER["false_easting",200000],PARAMETER["false_northing",8000
000],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AUTHORITY["EPSG","32107"]]
"

so if you know your data is not in Nevada - you guessed wrong about the
spatial reference system

Well even if its in the range doesn't necessarily mean you have the
right projection. 

The trick I normally use when I have no clue what projection a data set
is in but I have some guesses e.g. I know its a meter projection or the
state etc) and I know say the long lat of a point that should be in that
range would be something like below (and that usually 0s down to 1 or 2
likely candidates).  If the projection doesn't exist in spatial_ref_sys
(or I have the ESRI .prj file) - then I go to
http://spatialreference.org and do some searches and load up some likely
culprits in my spatial_ref_sys table and retry the below db or upload
the prj to spatial ref.

 SELECT srid, srtext, proj4text
FROM spatial_ref_sys 
WHERE proj4text ILIKE '%units=m%' AND srtext ILIKE '%NAD%' 
AND ST_Transform(ST_SetSRID(ST_MakePoint(-71.015,42.372), 4326), srid)
&& 
	ST_Expand(ST_SetSRID(ST_MakePoint(239898, 902552), srid),1000)

Hope that helps,
Regina
________________________________

From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of R H
Sent: Thursday, September 11, 2008 11:42 AM
To: PostGIS Users Discussion
Subject: RE: [postgis-users] Need Help with Transform

Thanks for the Help Regina, below are some of the points I attempted.

setsrid(MakePoint(834934.2263,26712690.6089, 32107) 
setsrid(MakePoint(834533.210694,26712881.1962, 32107) 
setsrid(MakePoint(834224.086891,26712318.3331, 32107) 

Is there a way to check if it is in the range of the projection? 

________________________________

From: lr at pcorp.us
To: postgis-users at postgis.refractions.net
Subject: RE: [postgis-users] Need Help with Transform
Date: Fri, 5 Sep 2008 18:19:58 -0400

RH,

This kind of thing happens if your input points are not actually in the
projection you say they are with setsrid.

Give us an example 32107 point you are using.  I suspect it doesn't fall
in the range of a valid 32107 point.

Hope that helps,
Regina

________________________________

From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of R H
Sent: Friday, September 05, 2008 1:13 PM
To: postgis-users at postgis.refractions.net
Subject: [postgis-users] Need Help with Transform

________________________________

Transform is returning to the same value, for different inputs?  Below
is what I have done...

select AddGeometryColumn('data_stage', 'table', 'geo4269', 4269,
'POINT', 2)
select AddGeometryColumn('data_stage', 'table', 'geo32107', 32107,
'POINT', 2)

update table
set geo32107= setsrid(MakePoint(x, y), 32107) 
where ....

update table set geo4269 = transfrom(geo32107, 4269)
where ....

column geo4269 all have the same vaule.  select AsText(geo4269) returns
'POINT(-115.583333333333 90)' for all rows.  And select AsText(geo32107)
returns the point as input.

Am I using transform wrong?  Or any other problems?  Any help many
thanks...

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