[postgis-users] Selecting geocoded postal codes within a given distance ( miles for example )

[Hugh W. O'Brien]

Thanks for the reply Paul.  I had come to the conclusion that I had 
those 2 choice but wasn't sure which one was more difficult.  Thanks for 
pointing out which one is easier to implement.

Now for a followup question?

What's the best way to convert my geocoded postal codes to UTM?

What would be the appropriate SRID of my new data set if I chose UTM as 
my new rectangular cooridinate set?

-- Hugh W. O'Brien

Paul Ramsey wrote:

> You have a couple options.
>
> One is to take your whole data set and translate it into a planar 
> projection. If you have a contrained area, that might be a good thing 
> to do, because it makes the whole problem simpler.
>
> Two is to essentially two-stage the problem. Problem (a) is subsetting 
> your complete data set to just those codes which *might* be within 
> your radius. Problem (b) is explicitly testing those codes. To do (b) 
> on a lat/lon data set, you need to know the ratio of miles/degrees 
> longitude and miles/degrees latitude for your area. You can calculate 
> these with a couple selects using length_spheroid and two-point 
> LINESTRINGS constructed in our search area. Then you use these 
> distances to construct a query box, and used distance_spheroid() to 
> parse out just those codes which fall in your search area.
>
> You can see why option one is simpler :)
>
> Hugh W. O'Brien wrote:
>
>> Dear List,
>>
>> How would one go about selecting the geocoded postal codes within 
>> given a distance ( say in miles ) of another geocoded postal code.  
>> Finding the long/lat of the postal code we are searching around is 
>> simple ( no help is needed there ). I have read/seen the faq for 
>> postgis.  The example given  there using a bounding box doesn't 
>> really fit what I am trying to do exactly because I will be dealing 
>> with degrees longitude/latitude and miles ( the example in the faq 
>> uses meters exclusively ).
>>
>> Thanks in advance for any help you can give.
>>
>> -- Hugh W. O'Brien
>>
>>
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