Re: [mapserver-users] Shapefile spatial index challenge

[Fawcett, David (MNIT)]

I have seen examples where for the purpose of overlay operations, someone chops 
up their large polys into smaller ones, each with an attribute that contains 
the id for the large poly.  I don’t know if that would fit your use case.

David.

From: mapserver-users [mailto:mapserver-users-boun...@lists.osgeo.org] On 
Behalf Of Ben Madin
Sent: Friday, October 23, 2015 1:23 AM
To: Lydon Chandra
Cc: mapserver-users@lists.osgeo.org
Subject: Re: [mapserver-users] Shapefile spatial index challenge

G’day Lydon,

I feel your pain, but there is little benefit to creating more quadrants. The 
idea (as I understand it - could be wrong) is to be able to use a (fast) 
bounding box to find the polygons to test, rather than having to test against 
every polygon using more complex algorithms.

I suppose you could consider that if you want to find out if a point is in one 
or more of your polygons, the benefit of having more index squares. You only 
have 8 polygons (I presume) so this should limit you in most cases to only 
having to compare your ‘point’ with only a couple of polygons using the more 
complex algorithms.

hth

cheers

Ben




On 2015-10-08, at 21:31 , Lydon Chandra 
mailto:lydon_chan...@technologyonecorp.com>>
 wrote:

Hi List,

How can we generate more quadrants for the spatial index for the Australia 
polygon below ?

Using MapServer shptree, even forcing it to go to 50 level deep, the spatial 
index does not have more quadrants.

More data and details at:
http://www.evernote.com/l/AhrYASBGtqVOkJn0BLqZkceADvOsA_UBfvY/





Kind Regards,
Don




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Ben Madin

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Re: [mapserver-users] Shapefile spatial index challenge

[Ben Madin]

G’day Lydon,

I feel your pain, but there is little benefit to creating more quadrants. The 
idea (as I understand it - could be wrong) is to be able to use a (fast) 
bounding box to find the polygons to test, rather than having to test against 
every polygon using more complex algorithms. 

I suppose you could consider that if you want to find out if a point is in one 
or more of your polygons, the benefit of having more index squares. You only 
have 8 polygons (I presume) so this should limit you in most cases to only 
having to compare your ‘point’ with only a couple of polygons using the more 
complex algorithms.

hth

cheers

Ben




> On 2015-10-08, at 21:31 , Lydon Chandra  
> wrote:
> 
> Hi List,
> 
> How can we generate more quadrants for the spatial index for the Australia 
> polygon below ?
> 
> Using MapServer shptree, even forcing it to go to 50 level deep, the spatial 
> index does not have more quadrants.
> 
> More data and details at:
> http://www.evernote.com/l/AhrYASBGtqVOkJn0BLqZkceADvOsA_UBfvY/ 
> 
> 
> 
> 
> 
> 
> Kind Regards,
> Don
> 
> 
> 
> 
> ___
> mapserver-users mailing list
> mapserver-users@lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/mapserver-users


-- 

Ben Madin

t : +61 8 6102 5535
m : +61 448 887 220
e : b...@ausvet.com.au

AusVet Animal Health Services

18/27 Market Street, Fremantle
Western Australia

AusVet's website:  http://www.ausvet.com.auFind our office: 
http://w3w.co/leader.code.frozen

This transmission is for the intended addressee only and is confidential 
information. If you have received this transmission in error, please delete it 
and notify the sender. The contents of this email are the opinion of the writer 
only and are not endorsed by AusVet Animal Health Services unless expressly 
stated otherwise. Although AusVet uses virus scanning software we do not accept 
liability for viruses or similar in any attachments. Thanks for reading. The 
average disclaimer at the bottom of an email is probably never read but 
contributes substantially to increasing the size of packet being sent through 
the internet and ultimately congestion.

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Re: [mapserver-users] Shapefile spatial index challenge

[Rahkonen Jukka (MML)]

Hi,

I am not sure what you are aiming at. Your shapefile has 9 features. Shptree 
documentarion says “The quadtree method breaks the file into 4 quadrants, 
recursively until only a few shapes are contained in each quadrant”. I guess 
that with the current shptree code it is impossible to build quadrants so that 
they would contain less than one feature.

What actually is your issue? Perhaps there is something else to improve than 
fiddling with the indexing of partial features.

-Jukka Rahkonen-


Lydon Chandra wrote:

Hi List,

How can we generate more quadrants for the spatial index for the Australia 
polygon below ?

Using MapServer shptree, even forcing it to go to 50 level deep, the spatial 
index does not have more quadrants.

More data and details at:
http://www.evernote.com/l/AhrYASBGtqVOkJn0BLqZkceADvOsA_UBfvY/





Kind Regards,
Don




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[mapserver-users] Shapefile spatial index challenge

[Lydon Chandra]

Hi List,

How can we generate more quadrants for the spatial index for the Australia
polygon below ?

Using MapServer shptree, even forcing it to go to 50 level deep, the
spatial index does not have more quadrants.

More data and details at:
http://www.evernote.com/l/AhrYASBGtqVOkJn0BLqZkceADvOsA_UBfvY/


[image: Inline image 1]


Kind Regards,
Don
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