[udig-devel] How to create a grid of features in a polygone

[Ingmar Eveslage]

Just for an update: i (to be honest: a colleague) found this class:

http://udig.refractions.net/files/docs/api-geotools/org/geotools/referencing/GeodeticCalculator.html

i think this could help to do the job in a plugin source code.

greats ingmar

Am 30.03.2008 um 19:20 schrieb andrea antonello:
> Hi Ingmar,
>
>>>> Good idea with to intersection of the horizontal and vertical  
>>>> lines.
>>>> But how do i create the lines with the constant spacing?
>>>>
>>>> i manged to get the envelope from a polygone with 5 coordinates  
>>>> likes
>>>> this:
>>>>
>>>> (13.68264407681451, 53.818121066825206, NaN)
>>>> (14.101893321395334, 53.818121066825206, NaN)
>>>> (14.101893321395334, 54.112935604110326, NaN)
>>>> (13.68264407681451, 54.112935604110326, NaN)
>>>> (13.68264407681451, 53.818121066825206, NaN)
>>>>
>>>> a nice bounding box. and now?
>>>>
>>>> the first horizontal line is
>>>>
>>>> (13.68264407681451, 54.112935604110326, NaN) (14.101893321395334,
>>>> 54.112935604110326, NaN)
>>>>
>>>> the upper left corner to the upper right corner. how do i get the
>>>> next
>>>> point for the Y coordinate with a distance of, lets say, 200m?
>>>>
>>>> (13.68264407681451, ??, NaN) (14.101893321395334, ??, NaN)
>>>
>>> You are dealing with lat-long coordinates, so it doesn't make  
>>> sense to
>>> talk metric.
>>> You could say: "...point for the Y coordinate with a distance of,  
>>> lets
>>> say, 60'?"
>>> If you need metric, you should first reproject the layer into your
>>> local metric system and then do maths with your metric coordinates.
>>>
>>> Is that the problem you have?
>>
>> Yes, i think this is my problem. I can not deal with a distance of
>> 60'. How can i do this projection? I am not realy good in this geo-
>> stuff. sorry.
>>
>> lets resume what i should do:
>>
>> i have lat/lon -> project in metric coodinates (km, meter) -> take  
>> the
>> line and calculate a parallel line with distance of 200m -> reproject
>> to lat/lon to get the depending coordinates.
>>
>> is this possible? how?
>
> It is possible.
> Load your shapefile or whatever. Export it. When you export it, you
> can choose the CRS for the exported map. Choose the epsg for your
> projection. That one you have to be aware of, because if you do not
> have exactly the info required, you could have shifts and distortions.
>
> Once exported it is also reprojected. Load the new shapefile and you  
> are there.
> Now the part with the lines and 200m comes.
>
> Onces you have the final points, you can reproject them nack, even if
> they are reprojected *for visualization only* on the fly.
>
> Andrea
>
>
>>
>> Thanks forward.
>>
>>
>>
>>> Ciao
>>> Andrea
>>>
>>>
>>>
>>>>
>>>> Thanks again. Ingmar
>>>>
>>>> Am 30.03.2008 um 15:21 schrieb andrea antonello:
>>>>
>>>>
>>>>>> i have a little "geospatial" question. I want to draw polygones
>>>>>> on a
>>>>>> polygone layer and then start a wizard which fills the polygone
>>>>>> with
>>>>>> features (with a point geometry). All features have the same
>>>>>> distance
>>>>>> (lets say 100m to each other) and all are in the area of the
>>>>>> polygone.
>>>>>>
>>>>>> Sounds like a not so difficult problem, but i hope that there  
>>>>>> is a
>>>>>> nice way to program this. perhaps i should use the gridcoverage
>>>>>> class?
>>>>>> i realy dont know where to start.
>>>>>
>>>>> Hi Ingmar,
>>>>> I think it is more a JTS related question.
>>>>> What I would probably do (I'm writing as I'm thinking) is to  
>>>>> create
>>>>> the grid of lines at the wanted distances one from the other.
>>>>> The horizontal lines and vertical lines should stay in two  
>>>>> different
>>>>> multilinestring geometries. Then through
>>>>>
>>>>> resultPointGeom = horizontalLines.intersection(verticalLines)
>>>>>
>>>>> you gain all the points you wanted to have into the resulting
>>>>> geometry.
>>>>> After that you will have to get from those only the ones inside  
>>>>> the
>>>>> polygon, which I assume can be done through another intersection
>>>>> between polygon and resultPointGeom.
>>>>>
>>>>> Ciao
>>>>> Andrea
>>>>>
>>>>>
>>>>>
>>>>>>
>>>>>> Thanks for any advice.
>>>>>>
>>>>>> Greats Ingmar
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