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I am no expert in this but from my understanding: The OpenLayers plugin in QGIS uses the EPSG:3857 CRS which is a projected CRS on a flat surface (here's a very good post describing it). Therefore, it calculates a straight-line distance as you would on a paper map. I can't find how Google Maps calculates its distances but a common method would be to use ...


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(1) Use GME available from http://www.spatialecology.com/ (2) otherwise use the "Point distance tool" from the geoprocessing tools of ArcGIS - for proximity calculations to find the object distance in the same layer. You can specify search radius. I hope this will help..


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As an approximation suitable for medium-small radii, use the cos() of the latitude to scale up the true distance to a "distance" that makes sense for your latitude in web mercator, as described here. SELECT * FROM mytable WHERE ST_DWithin( ST_Transform(ST_SetSRID(ST_MakePoint(%lon, %lat), 4326), 3857), the_geom_webmercator, %radius / cos(%lat * ...


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As you have specified that the line from the point can pass in/out of the polygon then I think all you need to do is extract the Envelope of the polygon. You also state in the comment above you are look for an arcpy solution and you have a Basic license level. You can get most of the way with model builder and a sneaky use of the fishnet tool to extract the ...


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"Erroneous" is relative to your accuracy needs. Let us therefore estimate the accuracy in terms of the distance the boat has traveled: by means of such a result, you can decide when positional calculations become "erroneous." I understand the question as saying that mapping is carried out in an azimuthal equidistant coordinate system centered at the boat's ...


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you can't really convert convert distances in degrees into meters as the size of a degree varies as you approach the poles. convert your locations into a projected coordinate system, then calculate your distances.


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The documentation for Near Analysis indicates "NEAR_DISTANCE: The distance between the input and near feature. The value is in the linear unit of the input features coordinate system, or Meters when the Method parameter is set to GEODESIC and the input is in a geographic coordinate system." So my understanding of that statement is: A Geographic Coordinate ...


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It is due to the projection of a 2D plane onto a polorised 2 spheres surface, as the line moves past the poles, it becomes distorted as far as observers of the 2D plane are concerned because the straight line to the destination appears to be a curved ark of a Great Circle, which is a term in mathematics that relates to the greatest circle that can be sliced ...



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