[postgis-users] srid

[Bob Pawley]

I considered ST_Translate but the float 8 seems to require an offset in feet 
or meters.

Perhaps I am wrong about that?

Bob
----- Original Message ----- 
From: "Andy Anderson" <aanderson at amherst.edu>
To: "PostGIS Users Discussion" <postgis-users at postgis.refractions.net>
Sent: Monday, May 26, 2008 7:46 PM
Subject: Re: [postgis-users] srid


It seems like you might be better off using ST_Translate() to
translate an object's location than to use ST_Transform() to change
the underlying spatial reference. If you want to draw objects on the
same canvas, you need to have them in the same spatial reference;
that's the purpose of ST_Transform(). If you can start with everything
in the same spatial reference and merely translate them around, I
would think it would involve a lot less processing.

-- Andy

On May 26, 2008, at 9:33 PM, Bob Pawley wrote:

> That is what I am attempting.
>
> I know of Visio. My thought of using Postgis is to, if possible, use  the 
> functions that Postgis provides. In the very long range I was  also 
> considering the 3D aspect of Postgis.
>
> Your suggestion of using "boxes", presumably to provide reference  points 
> is my backup method, if ST_Transform isn't applicable.
>
> I would still like to consider ST_Transform as it appears to be a  more 
> flexible approach.
>
> Bob
>
>
> ----- Original Message ----- From: "Chris Hermansen" 
> <chris.hermansen at timberline.ca
> >
> To: "PostGIS Users Discussion" <postgis-users at postgis.refractions.net>
> Sent: Monday, May 26, 2008 6:05 PM
> Subject: Re: [postgis-users] srid
>
>
>> Or, in another direction... Bob, if your "geometrical data" is  meant to
>> be something like a "data flow diagram" or a "process diagram", you  can
>> surely do that with PostGIS.
>>
>> Doubtless you must be aware of tools like Visio (in Windoze) or Dia  (in
>> Linux or Windoze) that are made for drawing diagrams like "data  flow",
>> but nevertheless you've decided to put your data into PostGIS  instead.
>>
>> Then you probably want to make some "boxes" in your process diagram
>> appear above, below, to the right of, or to the left of, other boxes.
>>
>> To do that, you would need to define some kind of partial order on  the
>> boxes (this box is to the right of that box, etc).  This sounds  like a
>> topological sort to me.
>>
>> Presumably you could turn that topological ordering into some set of
>> offsets that could be applied to compute coordinates of each box.
>>
>> is that where you're trying to end up?
>>
>> Andy Anderson wrote:
>>> On May 26, 2008, at 3:06 PM, Bob Pawley wrote:
>>>
>>>> However, I attempting to interpret functions made for geographic  data
>>>> to use with geometric data.
>>>>
>>>> I have PostgreSQL tables which represent engineering processes.
>>>>
>>>> I want to display that data in a graphical form - hopefully using
>>>> Postgis - - - if I can translate the functions (or the Postgis
>>>> concept) into a form that I can use.
>>>
>>> Hmmm... if all you want to do is display X-Y data, I would suggest
>>> using geographic coordinates, e.g. SRID = 4326 (WGS84 datum), which
>>> most programs will display by default with X and Y rectilinear.
>>>
>>> However, you earlier said you wanted to use ST_Transform(geometry,
>>> integer), which implies you want to switch between different 
>>> geographies.
>>>
>>> So it sounds like you need to pick a particular projection for  your 
>>> work.
>>>
>>> Is your geography spherical or spheroidal? If so, you might want to
>>> define your own datum. If not, you'll need to use a projection to a
>>> flat surface. What's more important, that it be conformal
>>> (equiangular) or equal area or that it preserve distance in one
>>> direction?
>>>
>>> -- Andy
>>> _______________________________________________
>>> postgis-users mailing list
>>> postgis-users at postgis.refractions.net
>>> http://postgis.refractions.net/mailman/listinfo/postgis-users
>>
>>
>> -- 
>> Regards,
>>
>> Chris Hermansen         mailto:chris.hermansen at timberline.ca
>> tel+1.604.714.2878 · fax+1.604.733.0631 · mob+1.778.232.0644
>> Timberline Natural Resource Group · http://www.timberline.ca
>> 401 · 958 West 8th Avenue  · Vancouver BC · Canada · V5Z 1E5
>>
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