[mapserver-users] Arc symbol.

[Marek Bąk]

Hi All,

Thanks for all suggestions and ideas. I've evaluated them using the ms4w 
binaries (v3.3.0):
- there is no support for V8 at the moment (unless built from sources),
- adding ST_Project to spatialite library is on roadmap (at the moment 
you need to compile spatialite library yourself),
- I failed with CIRCULARSTRING - when I used select with ST_GeomFromText 
and CIRCULARSTRING as geometry the result was null (I guess that I've 
missed something),
/- /I did not test PostGIS but I think that it should work (I guess all 
required function are there).

Instead of all above, since I'm working on S-57 LIGHTS layer and I've 
already needed a shape file for storing each light description, I've 
decided to convert S-57 ENC LIGHTS layer to two shape files (one for 
POINTS and one for LINES). I still need to tweak that solution but it 
seems to work (one layer became physically two but since I'm using GROUP 
attribute in LAYER object logically it was one to one conversion).

Regards,
Marek


> Hi Marek,
>
> This is a way of making arcs in Mapserver that is based on using VRTs 
> and sql
> The data source doesn't need to be in spatialite though. It can be a 
> shapefile
> or a CSV file or anything that gdal can handle.
>
> Simon Mercier at Mapgears and I developed this for making litehouse 
> circles
> for Sea charts a couple of years ago. In the current version of the
> SMAC-M project this is done with preprocessing in another way.
>
> But I still like the idea that You can draw anything with sql.
>
> I was going to make a small separate example this morning.
> But I ran into some problems. It seems like my current gdal is not
> compiled with a version of libspatialite that should use
> librttopo instead of the lwgeom. In the version I used before I had the
> sql function ST_project. In the version I had today on my machine and 
> in some docker
> containers I didn't. I guess I have to build a gdal-mapserver with
> the right libspatialite and librttopo versions where I can do
> these trix again some time.
>
> Anyway this is the VRT file that can draw an arc in Mapserver.
> The data source contains points in EPSG 4326 and we are drawing the arc
> in EPSG 3857 in this case. valnmr is the radius and sectr1 and sectr2 are
> starting and ending angles of the arc.
>
> To use the vrt in mapserver you use:
>
> CONNECTION "arc.vrt"
> CONNECTIONTYPE OGR
> DATA "arc"
>
> ###### arc.vrt #####
> <OGRVRTLayer name='arc'>
> <SrcDataSource>coastal.sqlite</SrcDataSource>
> <SrcSQL dialect='sqlite'>
> SELECT rcid,fidn,valnmr,sectr1,sectr2,colour,SIGGRP,SIGPER,HEIGHT,
> MakeArc(ST_X(Transform(Geometry,3857)),ST_Y(Transform(Geometry,3857)),
> GLength(Transform(MakeLine( MakePoint( X(Geometry), Y(Geometry),4326),
> ST_Project( MakePoint( X(Geometry), Y(Geometry), 4326 ),
> valnmr*1852/10, Radians( sectr1-180 ))),3857)),
> (180-(sectr2-90)),(180-(sectr1-90)),3857,2) AS geometry
> FROM lights_point
> WHERE sectr1 NOT NULL AND sectr2 NOT NULL AND sectr1!=0 AND sectr2!=360
> </SrcSQL>
> </OGRVRTLayer>
> #######################
>
> If You would like to check what version of various libraries that You
> have, You can use this VRT and run ogrinfo on it. E.g ogrinfo 
> debug.vrt debug
>
> ##### debug.vrt #####
> <OGRVRTDataSource>
> <OGRVRTLayer name='debug'>
> <SrcDataSource>coastal.sqlite</SrcDataSource>
> <SrcSQL dialect='sqlite'>
> select
> sqlite_version(),
> spatialite_version(),
> lwgeom_version(),
> geos_version(),
> proj4_version()
> FROM lights_point
> </SrcSQL>
> </OGRVRTLayer>
> #####################
>
> Have fun !
>
> Lars Schylberg


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