[postgis-users] WKB Geometry Column

[Paul Ramsey]

Sean,

You are confusing storage format with inout/output format. No matter how 
you get data *into* postgis, it will be stored the same way, using the 
same internal structure. You have three choices for getting data into 
and out of postgis:

- Use the "canonical format". This is a string representation of the 
internal format. It might change, if we want to change the internal 
format. It currently looks a lot like WKB, but it is not. You can see 
the canonical format by going "select geom_column from geom_table".
- Use WKT. This is a human readable form of the geometry, using numbers 
and brackets and whatnot.  You can see the WKT format by going "select 
astext(geom_column) from geom_table".
- Use WKB. This is a computer readable form of hte geometry, a 
byte-stream.  You can see the canonical format by going "select 
asbinary(geom_column) from geom_table".

The only thing that is "faster" about WKB is your handling of it on the 
client side. It is much faster for client software to parse the 
byte-stream than it for it to parse WKT. PostGIS itself will not have 
noticably different performance if you use WKB or WKT on output.

Paul

Sean M. Montague wrote:

> I figured out how to insert GeomFromWKB, which makes me realize that I
> may be misunderstanding WKB.  My interest in postGIS is for creating SVG
> and I'm transitioning from an Avenue/ArcObjects background to web based
> implementation utilizing SVG, PHP, and hopefully postGIS.  I admit my
> knowledge of databases is lacking.  Previously I used MySQL, which is a
> lot easier to find answers to questions that I, as a novice to
> intermediate database user, have.  I try to avoid posting a question
> unless my search for an answer has turned up nothing.  I have come a
> long way, but I'm still trying to grasp conceptually what is going on in
> PostGIS.  What I don't get is how to utilize the WKB ability of postGIS.
> I read that shp2pgsql will insert as WKB, but after much searching, I
> have failed in figuring out how.  Where I read this didn't say how.
> Below is what I have figured out so far.  I extracted a poly from the
> database asBinary(geom) and printed it out into my SVG file.  I then
> viewed source and copied the poly binary string and placed it into the
> insert statement which worked, but the resulting geom in the new table
> is WKT, or what I believe to be WKT.  
> 
> INSERT INTO table1 (the_geom)
> VALUES
> (GeomFromWKB('01060000000100000001030000000100000005000000000000C0331E59
> C100000080D0874DC1000000C0331E59C1000000C0D42D58410000000053085041000000
> C0D42D5841000000005308504100000080D0874DC1000000C0331E59C100000080D0874D
> C1',32767));
> 
> In the database, the above Insert creates a table where the geom is
> stored identically as if I had inserted with WKT.  What is it that I
> don't know about WKB?  I understand that WKB is faster, which explains
> my interest in it.  I thought that it would be stored as binary in the
> database.  Any insight would help.
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