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Using geographic data

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Arturo Zambrano

Using geographic data

Hi All,

I would like to get some advice regarding which path I should take.

Problem:

Given a coordinate I want to know to which geographical object it belongs to.

Path 1

Using Glorp to make a query to a Postgis instance containing the boundaries of the geobjects

Path 2

Use the data form GADM data (according to this thread).

I would avoid path 1 in order to avoid installation of postgi. From the

thread mentioned above, I thing that it requires some development.

Regarding Path 2, I don't see which framework or library should I use to

import and query the data contained in the KMZ from GADM.

Any advice is welcome.

Best regards.

Art

Sven Van Caekenberghe-2

Re: Using geographic data

Arturo,

In Pharo itself, you could just do it yourself, like this:

T3GeoTools class>>#is: position inside: polygon
"T3GeoTools is: 5.33732@50.92601 inside: { 5.48230@50.82249. 5.49523@50.81288. 5.50138@50.82008. 5.50228@50.82595. 5.49265@50.82560. 5.48230@50.82249 }"

"T3GeoTools is: 5.49007@50.82205 inside: { 5.48230@50.82249. 5.49523@50.81288. 5.50138@50.82008. 5.50228@50.82595. 5.49265@50.82560. 5.48230@50.82249 }"

"Point in polygon - ray casting algorithm - http://www.ecse.rpi.edu/Homepages/wrf/Research/Short_Notes/pnpoly.html"

| inside otherIndex |
inside := false.
otherIndex := polygon size.
polygon doWithIndex: [ :each :index | | other |
other := polygon at: otherIndex.
(((each y > position y) ~= (other y > position y))
and: [ position x < (((other x - each x) * (position y - each y) / (other y - each y)) + each x) ])
ifTrue: [ inside := inside not ].
otherIndex := index ].
^ inside

Inside circle, rectangle etc are trivial.

Sven

> On 25 Jul 2015, at 01:19, Arturo Zambrano <[hidden email]> wrote:
>
> Hi All,
> I would like to get some advice regarding which path I should take.
>
> Problem:
> Given a coordinate I want to know to which geographical object it belongs to.
>
> Path 1
> Using Glorp to make a query to a Postgis instance containing the boundaries of the geobjects
>
>
>
> Path 2
> Use the data form GADM data (according to this thread).
>
>
> I would avoid path 1 in order to avoid installation of postgi. From the
> thread mentioned above, I thing that it requires some development.
>
>
> Regarding Path 2, I don't see which framework or library should I use to
> import and query the data contained in the KMZ from GADM.
>
>
> Any advice is welcome.
>
> Best regards.
> Art
>
>

hernanmd

Re: Using geographic data

In reply to this post by Arturo Zambrano

Hi Arturo,

Do you want to implement a Geolocator like NAC? http://www.nactag.info/map.asp

The GADM world tree is built from a CSV which I generated from the GADM 2.0 dBase files for the whole world. I checked the dBase format and doesn't include the polygon information you find in the .kmz files. I saw they released 2.5 this month (July 2015) but only in ESRI geodatabase format (which I didn't investigated yet, but not the same as ESRI shapefile format) and will release 2.7 in August 2015.

Another way could be just to parse the KML (is just an XML file) using XPath or XMLPullParser.

About locating the point in a polygon the problem of traditional 2D inclusion tests (ray crossing methods) is that require large storage, given polygons of enough size, complexity and amount of edges. This is a common situation with level 1 and 2 polygons. New methods for example classiffy polygon edges into layers, results in faster inclusion test.

Hernán

2015-07-24 20:19 GMT-03:00 Arturo Zambrano <[hidden email]>:

Hi All,
I would like to get some advice regarding which path I should take.

Problem:
Given a coordinate I want to know to which geographical object it belongs to.

Path 1
Using Glorp to make a query to a Postgis instance containing the boundaries of the geobjects

Path 2
Use the data form GADM data (according to this thread).

I would avoid path 1 in order to avoid installation of postgi. From the
thread mentioned above, I thing that it requires some development.

Regarding Path 2, I don't see which framework or library should I use to
import and query the data contained in the KMZ from GADM.

Any advice is welcome.

Best regards.
Art

Arturo Zambrano

Re: Using geographic data

In reply to this post by Sven Van Caekenberghe-2

Thanks Sven,

I will test the performance... some my objects have around

10000 points.

Maybe I will reduce the amount of point and sacrifice some precision.

I thought something like that was already available in SH.

Best regards

On Sat, Jul 25, 2015 at 4:31 AM, Sven Van Caekenberghe <[hidden email]> wrote:

Arturo,

In Pharo itself, you could just do it yourself, like this:

T3GeoTools class>>#is: position inside: polygon
"T3GeoTools is: 5.33732@50.92601 inside: { 5.48230@50.82249. 5.49523@50.81288. 5.50138@50.82008. 5.50228@50.82595. 5.49265@50.82560. 5.48230@50.82249 }"

"T3GeoTools is: 5.49007@50.82205 inside: { 5.48230@50.82249. 5.49523@50.81288. 5.50138@50.82008. 5.50228@50.82595. 5.49265@50.82560. 5.48230@50.82249 }"

"Point in polygon - ray casting algorithm - http://www.ecse.rpi.edu/Homepages/wrf/Research/Short_Notes/pnpoly.html"

| inside otherIndex |
inside := false.
otherIndex := polygon size.
polygon doWithIndex: [ :each :index | | other |
other := polygon at: otherIndex.
(((each y > position y) ~= (other y > position y))
and: [ position x < (((other x - each x) * (position y - each y) / (other y - each y)) + each x) ])
ifTrue: [ inside := inside not ].
otherIndex := index ].
^ inside

Inside circle, rectangle etc are trivial.

Sven

> On 25 Jul 2015, at 01:19, Arturo Zambrano <[hidden email]> wrote:
>
> Hi All,
> I would like to get some advice regarding which path I should take.
>
> Problem:
> Given a coordinate I want to know to which geographical object it belongs to.
>
> Path 1
> Using Glorp to make a query to a Postgis instance containing the boundaries of the geobjects
>
>
>
> Path 2
> Use the data form GADM data (according to this thread).

>
>
> I would avoid path 1 in order to avoid installation of postgi. From the
> thread mentioned above, I thing that it requires some development.
>
>
> Regarding Path 2, I don't see which framework or library should I use to
> import and query the data contained in the KMZ from GADM.
>
>
> Any advice is welcome.
>
> Best regards.
> Art
>
>

Arturo Zambrano

Re: Using geographic data

In reply to this post by hernanmd

Hi Hernán

On Sat, Jul 25, 2015 at 4:54 AM, Hernán Morales Durand <[hidden email]> wrote:

Hi Arturo,

Do you want to implement a Geolocator like NAC? http://www.nactag.info/map.asp

Nope, just to count points for each different province.

The GADM world tree is built from a CSV which I generated from the GADM 2.0 dBase files for the whole world. I checked the dBase format and doesn't include the polygon information you find in the .kmz files. I saw they released 2.5 this month (July 2015) but only in ESRI geodatabase format (which I didn't investigated yet, but not the same as ESRI shapefile format) and will release 2.7 in August 2015.

Another way could be just to parse the KML (is just an XML file) using XPath or XMLPullParser.

Of course,thanks. I wanted to know if there were a library supporting KMZ, and doing some queries on the objects contained there.

From your reply and Sven's , I see there is no such library, but it seems very easy to implement that functionality.

My only concern now is performance, I will try it and let you know.

About locating the point in a polygon the problem of traditional 2D inclusion tests (ray crossing methods) is that require large storage, given polygons of enough size, complexity and amount of edges. This is a common situation with level 1 and 2 polygons. New methods for example classiffy polygon edges into layers, results in faster inclusion test.

Thanks again.

best regards

art

Hernán

2015-07-24 20:19 GMT-03:00 Arturo Zambrano <[hidden email]>:
Hi All,
I would like to get some advice regarding which path I should take.

Problem:
Given a coordinate I want to know to which geographical object it belongs to.

Path 1
Using Glorp to make a query to a Postgis instance containing the boundaries of the geobjects

Path 2
Use the data form GADM data (according to this thread).

I would avoid path 1 in order to avoid installation of postgi. From the
thread mentioned above, I thing that it requires some development.

Regarding Path 2, I don't see which framework or library should I use to
import and query the data contained in the KMZ from GADM.

Any advice is welcome.

Best regards.
Art