[postgis-users] Minimum Bounding Rectangle

[Brent Fraser]

Madison,

   My algorithm will produce A rotated rectangle, but not necessarily 
THE minimum bounding rectangle.  My focus was on finding the length of a 
polygon, then the width perpendicular to that length (and my algorithm 
is ok for that).  JTS's getMinimumRectangle is the approach to use for a 
rotated MBR. Think of a square polygon; my approach will result in a 
larger square rotated 45 degrees from the original, whereas JTS will 
produce a square of the same size and orientation as the original (as 
would be expected for a rotated MBR).

   Sorry for the misdirection...

Best Regards,
Brent Fraser

On 6/19/2012 3:42 AM, Madison Shaw wrote:
> Thanks Martin - Ill have a look at JTS - otherwise I think I will be
> implemeting it based on the steps Brent mentions.
>
> I believe ArcGIS 10 has a set of tool to create them as well - but
> requires an info license.
>
> Thanks everyone for the help :)
>
> Madison
>
>
>
>
> On 19 June 2012 04:39, Martin Davis <mtnclimb at telus.net> wrote:
>> JTS has a class for computing a Minimum Bounding Rectangle:
>>
>> http://tsusiatsoftware.net/jts/javadoc/com/vividsolutions/jts/algorithm/MinimumDiameter.html
>>
>> This may be in GEOS as well.
>>
>>
>> On 6/18/2012 9:36 AM, Brent Fraser wrote:
>>> Madison,
>>>
>>>   I went looking a few months ago, but could find nothing.  I wrote some
>>> PHP to:
>>>     1. Find the length of the polygon (vertices farthest apart)
>>>     2. Find the width (based on vertices farthest from length line)
>>>     3. Build bounding box using length (with angle of the the length line)
>>> and the width
>>>
>>> I'm still pondering the result when the input polygon is a square...
>>>
>>> But there should really be something like a "ST_ExtentRotated" or
>>> "ST_RotatedBBox"  function in PostGIS.
>>>
>>> Best Regards,
>>> Brent Fraser
>>>
>>> On 6/15/2012 2:03 PM, Madison Shaw wrote:
>>>> Hi,
>>>>
>>>> I was wondering if any one could possibly offer some advice.
>>>>
>>>> I am wanting to calculate the area for a minimum bounding rectangle
>>>> for individual polygon features.  I know I can use st_envelope or
>>>> st_extent along with st_area but this doesn't quite give me the
>>>> results I am after.
>>>>
>>>> For example if the polygon was already a rectangle but was orientated
>>>> on an angle the bounding box area is much larger than the area of the
>>>> original rectangle, whereas I would like it to be the same value.  I
>>>> suppose what I am after is a convex hull but as a rectangle. Is this
>>>> possible?
>>>>
>>>> Any help is greatly appreciated.
>>>>
>>>> Cheers
>>>>
>>>> Madison
>>>> _______________________________________________
>>>> 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
>>>
>>>
>>> -----
>>> No virus found in this message.
>>> Checked by AVG - www.avg.com
>>> Version: 2012.0.2179 / Virus Database: 2433/5077 - Release Date: 06/18/12
>>>
>>>
>> _______________________________________________
>> 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
>