[Qgis-user] Velocity Difference Calculation?

[dean.walker151 at gmail.com]

Yeah, I’ve got a distance reference that covers the amount of distance covered in the time from the last point.  I’m just missing the way to actually do the calculation in the program.  I cant see a way to compare a point to the one before it.


Thanks!

Dean 






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From: Randal Hale
Sent: ‎Sunday‎, ‎August‎ ‎17‎, ‎2014 ‎3‎:‎22‎ ‎PM
To: dean.walker151 at gmail.com, qgis-user at lists.osgeo.org




I can think of a couple of ways you might be able to do this - but considering I haven't done something like this before it's a guess. 

You can derive an interval in seconds I believe (referencing http://nathanw.net/2012/06/30/better-date-and-time-support-in-qgis-expressions-and-styles/) from the point data  - I'm assuming you have date and time (or at least time). 

You could connect the points with a line (that would give you distance). 

I'm thinking this might be better accomplished in a database as opposed to a shapefile (assuming shapefile). 

...and I think I've just given you the most abstract assumed non-answer ever. 

Lemme think on this one a bit more. Hopefully someone has a practical answer. 

Randy





On 08/17/2014 05:57 PM, dean.walker151 at gmail.com wrote:




Hi all,




I’m working on some point data that has been collected using a combine in an agricultural field.  Trying to figure out a way to compare speed between the dropped points?  I’m not sure how to start….can anyone help?




Thanks

Dean






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