[postgis-users] srid

[Andy Anderson]

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
>>
>> _______________________________________________
>> postgis-users mailing list
>> postgis-users at postgis.refractions.net
>> http://postgis.refractions.net/mailman/listinfo/postgis-users
>
> _______________________________________________
> postgis-users mailing list
> postgis-users at postgis.refractions.net
> http://postgis.refractions.net/mailman/listinfo/postgis-users