Here's an example that I can think of. Suppose I digitize a bunch of linework from some old manuscripts that were hanging in a file cabinet, and they stretched. My control points were to the north of the data I digitized.
When I view the data that I digitized in conjunction with other existing data, I can see that it's about 100 metres south of where it should be. For this I would consider using ST_Transform() to shift my digitized data north by 100 metres. Something like ST_Transform(the_geom,0.0,100.0,0.0) Does that help? Bob Pawley wrote: > 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" > <[EMAIL PROTECTED]> > To: "PostGIS Users Discussion" <[email protected]> > 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" >>> <[EMAIL PROTECTED]> >>> To: "PostGIS Users Discussion" <[email protected]> >>> 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 >>>>> [email protected] >>>>> http://postgis.refractions.net/mailman/listinfo/postgis-users >>>> >>>> >>>> -- >>>> Regards, >>>> >>>> Chris Hermansen mailto:[EMAIL PROTECTED] >>>> 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 >>>> [email protected] >>>> http://postgis.refractions.net/mailman/listinfo/postgis-users >>> >>> _______________________________________________ >>> postgis-users mailing list >>> [email protected] >>> http://postgis.refractions.net/mailman/listinfo/postgis-users >> >> >> -- >> Regards, >> >> Chris Hermansen mailto:[EMAIL PROTECTED] >> 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 >> [email protected] >> http://postgis.refractions.net/mailman/listinfo/postgis-users > > _______________________________________________ > postgis-users mailing list > [email protected] > http://postgis.refractions.net/mailman/listinfo/postgis-users -- Regards, Chris Hermansen mailto:[EMAIL PROTECTED] 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 [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
