[ncl-talk] segments in shape must be closed circle?

[Mary Haley]

Yongli,

gc_inout will automatically close the polygon for you, so there's no need
to do this yourself.

See the description under:

http://www.ncl.ucar.edu/Document/Functions/Built-in/gc_inout.shtml

--Mary


On Thu, Dec 22, 2016 at 7:26 PM, Sitan Heyl <heylsitan at gmail.com> wrote:

> Hi, All
>>
>>    When I read the example 13 about shapefile (https://www.ncl.ucar.edu/
>> Applications/shapefiles.shtml), I found one confused code as follow. my
>> question is that if one geometry has two or more segments, need every
>> segments be closed circle or polygon, if not, how can this code directly
>> determine gc_inout in every segments?
>
> ;---Some Georgia counties have multiple segments
>     startSegment = geometry(ga_counties(i), geom_segIndex)
>     numSegments  = geometry(ga_counties(i), geom_numSegs)
>     do seg=startSegment, startSegment+numSegments-1
>       startPT = segments(seg, segs_xyzIndex)
>       endPT   = startPT + segments(seg, segs_numPnts) - 1
>
> ;---Loop through each point on data grid and see if it's in this county.
>       do n=0,nii_latlon-1
>         nn = ii_latlon(n)     ; Get index of point we're checking
> ;
> ; This "if" statement speeds up code, by making sure we don't
> ; needlessly check a lat/lon point if:
> ;
> ; - we've already found it in another county
> ; - it doesn't fall within the general lat/lon box that covers this county
> ;
>         if(skip_check(nn).or.\
>            lat1d(nn).lt.min(lat(startPT:endPT)).or.\
>            lat1d(nn).gt.max(lat(startPT:endPT)).or.\
>            lon1d(nn).lt.min(lon(startPT:endPT)).or.\
>            lon1d(nn).gt.max(lon(startPT:endPT)))
>            continue
>         end if
>
> ;---Here's the check if the point is in the county.
>         if(gc_inout(lat1d(nn),lon1d(nn),\
>                     lat(startPT:endPT),lon(startPT:endPT))) then
>           data_mask_1d(nn) = 1    ; This point is inside this county
>           skip_check(nn)   = 1    ; Don't check this point again
>         end if
>       end do
>
> end do ; End of collecting points for this county
>
> Best,
> Yongli
>
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