[postgis-users] Float 8

[Chris Hermansen]

Hmm, the form it takes?  Not sure I understand you.  Let me try
nevertheless.

A float8 is a single number.  It's 64 bits of floating point, part of
which is exponent and part of which is mantissa.  The exponent is
understood as a power of two.  The most common double precision floating
point representation in use today represents numbers to about 14 digits
of accuracy in the range of 10^-308 to 10^308, negative and positive. 
There are other special numbers like ± infinity and NaN (not a number).

Most computers use the IEEE 754-1985 standard for floating point.  You
can read all about this at http://en.wikipedia.org/wiki/IEEE_floating_point

A concrete example of a float8 number is 1.4976931341623151×10^3

What you are looking at specifically -
ST_Translate(geometry,float8,float8,float8) - takes a given geometry and
"translates" (ie moves relative to the origin) by the three float8
offset values you provide.  You might think of this as a shift.

Let's say you called ST_Translate() on a point (x,y,z) with offset
values (a,b,c).  Then your translated coordinates would be:

x' = x + a
y' = y + b
z' = z + c

ST_Translate() is one of the three components of an affine
transformation, the other two being ST_Scale() and ST_RotateZ().

Does this help?

Bob Pawley wrote:
> Any suggestions on the form it takes (integer, cooridinate, binary)
> and how it is used with ST_Translate???
>
> Bob
>
> ----- Original Message ----- From: "Chris Hermansen"
> <chris.hermansen at timberline.ca>
> To: "PostGIS Users Discussion" <postgis-users at postgis.refractions.net>
> Sent: Thursday, May 22, 2008 1:48 PM
> Subject: Re: [postgis-users] Float 8
>
>
>> float8 is double precision, about 14 digits of precision to be precise
>> :-) plus a bigger allowable exponent than float4 or single precision.
>>
>> Bob Pawley wrote:
>>> Hi
>>>
>>> Would someone please tell me what is meant by float 8 in this
>>> function? I know they refere to x, y and z coordinates. (An example
>>> would help)
>>>
>>> ST_Translate(geometry, float8, float8, float8)
>>>
>>> Bob
>>> _______________________________________________
>>> 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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>
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-- 
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