Re: [postgis-users] Minimum Bounding Rectangle
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 mtncl...@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@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users ___ postgis-users mailing list postgis-users@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@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users ___ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
Re: [postgis-users] Minimum Bounding Rectangle
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 mtncl...@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@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users ___ postgis-users mailing list postgis-users@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@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users ___ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users ___ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
Re: [postgis-users] Minimum Bounding Rectangle
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@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users ___ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
Re: [postgis-users] Minimum Bounding Rectangle
Regina, Yep, I used ST_LongestLine to confirm my length calc. I didn't think my PostGIS fu was good enough to create a Postgresql function to find the width and construct a rotated bbox (maybe some day)... Thanks! Best Regards, Brent Fraser On 6/18/2012 11:28 AM, Paragon Corporation wrote: It's on my todo. well first step of my todo anyway. http://trac.osgeo.org/postgis/ticket/1332 Brent -- thinking of your idea Have you tried using ST_LongestLine? http://www.postgis.org/documentation/manual-svn/ST_LongestLine.html I'm hoping to get back to this ticket soon but tied up with other things. Thanks, Regina http://www.postgis.us -Original Message- From: postgis-users-boun...@postgis.refractions.net [mailto:postgis-users-boun...@postgis.refractions.net] On Behalf Of Brent Fraser Sent: Monday, June 18, 2012 12:37 PM To: PostGIS Users Discussion Subject: Re: [postgis-users] Minimum Bounding Rectangle 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@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users ___ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users ___ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users ___ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
Re: [postgis-users] Minimum Bounding Rectangle
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@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users ___ postgis-users mailing list postgis-users@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@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
[postgis-users] Minimum Bounding Rectangle
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@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
