[postgis-users] ESRI Shapes from database

[Lee Keel]

  _____  

From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Obe,
Regina
Sent: Wednesday, October 17, 2007 11:16 AM
To: PostGIS Users Discussion
Subject: RE: [postgis-users] ESRI Shapes from database

 

Lee,

 

Well here is an example I grabbed from somewhere.  But if I exceed the size
of the bytearray - I get one of the errors you describe.  That was why I
thought maybe your offsets are wrong and part of your array has terminators
embedded in it.

 

For example these casts work okay

SELECT (encode(E'\\002The'::bytea, 'hex'))::float
SELECT (encode(substring(E'\\002The'::bytea from 1 for 8), 'hex'))::float

SELECT (encode(substring(E'\\002The'::bytea from 2 for 8), 'hex'))::float

 

--Now if I try to go past the size of the bytea observe - this casts to
empty

SELECT (encode(substring(E'\\002The'::bytea from 5 for 8), 'hex'))

 

And if I then try to cast that empty to float

SELECT (encode(substring(E'\\002The'::bytea from 5 for 8), 'hex'))::float

 

I get the error 

ERROR:  invalid input syntax for type double precision: ""

 

Hope that helps,

Regina

 

  _____  

[Lee Keel] 

Regina,

 

Let me start by saying THANK YOU for all of your help on this.  I have been
trying the sample like you have above and I see what it is doing, but I
can't seem to get it to work with a value that I have.  

 

I am getting a hex string back from by bytea:

SELECT (encode(substring(esri_shape from cnt for 8), 'hex')) =
'E4A9F1517F0E2B41'

 

So in theory this should work:

SELECT (encode(substring(esri_shape from cnt for 8), 'hex'))::float

 

But instead I get 'invalid syntax for a double precision'.  In my C# code,
this hex value ('E4A9F1517F0E2B41') converts to 886591.660046872 using the
microsoft bit converter.  The bit converter converts the given hex into the
following bit array:

 

[0]: 228

    [1]: 169

    [2]: 241

    [3]: 81

    [4]: 127

    [5]: 14

    [6]: 43

    [7]: 65

 

I would appreciate any help you can continue to provide on this.

 

Thanks again,

Lee

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