[postgis-users] Float 8

[Bob Pawley]

Hi Chris

How is the float 8 number generated - manually??

Seems to me one should be able to generate it relationally. Perhaps that's 
the point I'm missing?

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 2:45 PM
Subject: Re: [postgis-users] Float 8


> 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
>>>> _______________________________________________
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>>>> postgis-users at postgis.refractions.net
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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
>>>
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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
>
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