[Geojson] Adding extra data to a geojson string

[Chitraleka Appalanaidu]

Hi Tim,

Thank you very much for your help. feature.cluster solved the problem.

For other users who come across this problem, try to get the attributes of a
point (specified in the geojson file in the 'properties' list) by using
feature.cluster[0].attributes.<name_of_attribute_key>

{
   "type": "FeatureCollection",
   "features": [
       {"type":"Feature", "id":"computer1", "properties":{"trial":"test"},
"geometry":{"type":"Point", "coordinates":[143, -35.91]}},
       {"type":"Feature", "id":"computer2", "properties":{"trial":"test"},
"geometry":{"type":"Point", "coordinates":[144, -37.81667]}}
   ]
}

Basically, this is what happens when the geojson fileabove is parsed by
OpenLayers.Format.GeoJSON parser and added as OpenLayers.Vector.Feature
objects into a OpenLayers Vector layer (that performs the clustering
strategy):
1. GeoJSON file is read by the GeoJSON parser.
2. Parser creates OpenLayers.Vector.Feature objects for each string.
3. These OpenLayers.Vector.Feature objects are then added to the OpenLayers
Vector layer
4. OpenLayers Vector layer performs clustering strategy
5. Each feature point that appears on the map is the top-level feature point
(for a group of clusters). The attributes for this feature point is:

undefinedlayer value :[object Object]
 lonlat value :null
 data value :[object Object]
 id value :OpenLayers.Feature.Vector_201
 geometry value :POINT(15918687.18122222 -4288244.5663272375)
 state value :null
 attributes value :[object Object]
 style value :null
 cluster value :[object Object],[object Object],[object Object]
//this indicates that this cluster point has three feature objects
underneath it
 renderIntent value :select
 marker value :null

6. As it can be seen above, there is a 'cluster' property that holds 3
objects (being the three points). Hence, if you drill down to the 'cluster'
property (i.e. feature.cluster[0]), it will give you the attributes of the
first object in the cluster (being the point):

undefined0 value :[object Object]
 layer value :null
 lonlat value :null
 data value :[object Object]
 id value :OpenLayers.Feature.Vector_197
 geometry value :POINT(8218510.393273033 -2699238.272071229)
 state value :null
 attributes value :[object Object]
 style value :null
 fid value :computer14
 marker value :null

7. From the above, it can be seen that the 'id' property from the geojson
file has been mapped to the 'fid' key of the feature point object. You can
also see that the 'attributes' key holds an [object Object]. If you do
feature.cluster[0].attributes.trial , it will display the 'trial' property
and value that you specified in the geojson file (i.e. 'test').


Hence, adding as many property-value pairs in the GeoJSON file is easy as
the GeoJSON parser just parsers the property-value pairs and enters the data
into feature point object attributes that are beneath the top-level cluster
point.

Kind regards,
Chitra



On Mon, Nov 2, 2009 at 12:56 PM, Tim Schaub <tschaub at opengeo.org> wrote:

> Hey-
>
>
> Chitraleka Appalanaidu wrote:
>
>> Hi all,
>>
>> I have a geojson file that I pass to the penLayers.Format.GeoJSON parser.
>> This parser converts the a geojson string (as below) to a
>> OpenLayers.Vector.Feature object and adds it into an OpenLayers Vector layer
>> (that performs clustering)
>>
>> {
>>    "type": "FeatureCollection",
>>    "features": [
>>        {"type":"Feature", "id":"computer1", "properties":{"trial":"test"},
>> "geometry":{"type":"Point", "coordinates":[143, -35.91]}},
>>        {"type":"Feature", "id":"computer2", "properties":{"trial":"test"},
>> "geometry":{"type":"Point", "coordinates":[144, -37.81667]}}
>>    ]
>> }
>>
>>
>> The problem with adding it into a clustering layer is that any properties
>> I add into the "properties":{} field in the above geojson file will get
>> overriden (because clustering will cause a count value to be entered into
>> the properties list).
>>
>> I would like to add other information about a point in the geojson file
>> above. Is there any other key-value pair i can use to do this? I have tried
>> the 'fid' and 'style' key-value pairs but the parser does not seem to parse
>> them out into a OpenLayers.Vector.Feature object.
>>
>>
> In terms of what you can do in GeoJSON, any other members (with
> non-reserved names) are allowed on feature objects.
>
> I think your issue is exclusively an OpenLayers issue.  OpenLayers will
> parse whatever you put in the properties member and make this available at
> feature.attributes (as you've seen).  When you use the cluster strategy, you
> can get at the original features in the cluster via feature.cluster.
>
> If you haven't already, you could write an email to the OpenLayers dev list
> with more specific questions.
>
> Tim
>
>  Thank you.
>>
>> Kind regards,
>> Chitra
>>
>>
>> ------------------------------------------------------------------------
>>
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>
>
> --
> Tim Schaub
> OpenGeo - http://opengeo.org
> Expert service straight from the developers.
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