Distance and area measurement

Development
9

Gareth:

Because the application continuously report the distance and area as it is
being measured, the stored data is on the format that you describe as a
line. The calculation is done such that the result is the area contained by
the shape that results by joining the end point and start point with a
straight line.

Chris:

I have to admit that I am not aware of exactly what capabilities you have
in ODK and it may very well be that you even want to rely on your own
distance and area functions. In particular, this application can only
handle areas small enough that the earths curvature is not significant,
like if measuring a whole continent or so, so if you can do better there is
certainly reason to use your own area calculation function). The reason I'm
reaching out to you is because I was informed a few years back by Eric
Cooper at Afsis that there was interest in incorporatingwhat was then my
android application into ODK and that some students at Stanford was trying
to do so during a Facebook hackathon. With the new website, this should be
much easier. Regarding what functionality that this brings, it is the
possibility to physically trace out paths by walking/driving around the
region of interest.

/Kristofer Björnson

··· On Thu, May 4, 2017 at 11:55 PM, Christopher Robert wrote:

BTW, there's already the area() function implemented in both Collect and
Enketo. And a distance-between(), I believe. How would the proposed
functionality be different?

Chris

On Thu, May 4, 2017, 5:42 PM xiphware@gmail.com wrote:

On Thursday, May 4, 2017 at 9:30:16 PM UTC+12, Kristofer Björnson wrote:

In my opinion the conversion to the XForm data format is best done on
the ODK side. We could attach hooks like

window.coordinateLogger.getGPSCoordinates();
window.coordinateLogger.getArea();
window.coordinateLogger.getDistance();

to the application itself, which returns a linear array of GPS
coordinates and two numbers, respectively.

Note: I cc Anna Sinelnikova who also is a developer of GEOruler.

Seems reasonsable. Would you distinguish returning a 'path' (line) vs
'shape' (closed polygon) by having the first and last GPS coords the same
(ie polygon) or not (ie line)? Not really an issue for getArea() - if
called you can assume polygon and treat whatever GPS coords as representing
a closed circuit. But for getDistance() I'm not sure how you'd determine
whether to return the path length (unclosed) vs perimeter (closed) of the
points...? Having the first and last coords of a polygon be the same would
eliminate any ambiguity.

  • Gareth

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