100m radius in projection 4326

Mar 9, 2011 at 5:04 PM
Edited Mar 9, 2011 at 5:22 PM

I need to draw a circle with a radius in meter in the projection 4326,

i'm able in a metric projection butif a tramform the layer in the circle look like a eclipse.

there is a way to determine the radius in degres ??? for a certain region. ???

 

i have look on the class ShapeFactory provide in previous post that work great but, what is missing it or to specify a radius of 100 m

 

Coordinator
Mar 9, 2011 at 5:44 PM

hello longuard, I'd go and pick an UTM Zone based on the center of the ellipse, and reproject the point to that utm zone.

When I have that, I'd use the shape factory to create the ellipse / circle and reproject that to wgs84.

Hth FObermaier

Mar 10, 2011 at 12:06 AM

http://en.wikipedia.org/wiki/File:Tissot_indicatrix_world_map_equirectangular_proj.svg

that explain my trouble ...

Coordinator
Mar 10, 2011 at 8:52 AM

If you don't want that, you need to

  • reproject your center,
  • create a point with an offset of 100 meters,
  • reproject that point to wgs84,
  • compute the "degee-distance" and
  • build the circle around the center with that distance.

Hth FObermaier

Mar 10, 2011 at 1:19 PM

hi

To reproject the layer there is not trouble me trouble is how to cumpute the "degree-distance".

 

Coordinator
Mar 10, 2011 at 1:57 PM

if your centroids are in a vectorlayer, I'd apply a CustomTheme, that exchanges the FeatureDataRow's geometry with the steps pointed out above.

the "degree-distance" would be the distance between original point to offset point in wgs84/epsg:4326 (originalPt.Distance(offsetWgs84);)

Hth FObermaier