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5

There is a python plugin for QGIS to calculate Tobler's Hiking function. It's called Walking times and you can install it using the qgis oficial repository. The plugin page explains how it works: http://sigsemgrilhetas.wordpress.com/plugins-qgis/walking-time/ And, since we are talking about open source, you can see and download all the code here: ...


3

You are absolutely correct. From wikipedia's Mercator projection: scale factor = secant (latitude) = 1 / cosine (latitude) Generally, divide map distance by the scale factor to get globe distance. But what about "long" lines, at different latitudes, what scale factor to use? According to EF Burkholder, for short lines, just calculate one scale factor ...


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In your case I would rather use "generate near table" in order to have the N closest lines. you can then apply your decision rules on the resulting table in order to select the points that match best. (remark : only available with advanced licence, unfortunately)


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There is no simple and accurate way to do it because ellipsoid. conversion to meters varies depending latitude. See : Length of a degree: where do the terms in this formula come from? one way to make it very simple (but not very accurate) is use table from http://en.wikipedia.org/wiki/Decimal_degrees. use 0.001 degrees and trigonometry to solve points


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You can create borders by using Polygon to Line tool for each polygon. Then use Near tool on these two borders.


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I would suggest to set a tolerance around the position of the the points (roughly 10 m) then your merge the position when the distance is below the tolerance. Similarly, you can run a kernel along your track to find out the average position. The tricky part is to also account for time in order to avoid merging two parallel tracks. another solution is to ...


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ST_Length, when called on a geometry, reports in units of the spatial reference system. For EPSG:900913/EPSG:3857, the units are in Mercator meters, not in meters. At all points on the globe, a Mercator meter is at most 1 real meter. To do this there are two possible fixes Transform to an appropriate projection for your area. UTM, state plane and albers ...



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