[JHV][HV] A reference measurement

[Jack Ireland]

In order to give members of the public an idea about the scale of the image they are looking at in JHV and HV.org, there should be an option to show some kind of reference measurement in the viewer window of JHV and HV.org. The reference measurement is a line of a fixed number of pixels length with a number and a unit next to it. The unit chosen refers to a well known object. The number changes depending on how zoomed in/out the view is, but the unit could change also depending on zoom. For example, when highly zoomed out the reference measurement could be a multiple of the size of the Earth i.e., 100 x Earth radius. On zooming in the reference measurement changes appropriately. At radii less than 1 Earth, the size scale could change to say, 'Atlantic Ocean', 'Europe', '10 x Rhode Island', etc. Metres or kilometers could also be given simultaneously, or via a toggle.

[Daniel Mueller (dmueller-esa)]

Hi Jack,

This would definitely be a nice functionality. However, one has to keep in mind that our data is not map-projected and the spatial scale varies significantly from the center of the disk to the limb.

At least for JHelioviewer, I would think that one would either

a) have to put in quite a bit of effort and make the displayed scale bar dependent on a given position on the Sun (e.g. mouse pointer position or the location of the scale bar itself)

b) Display the scale as an angular scale, and optionally add an conversion to a spatial scale at Sun center. (I am fully aware that not everyone is familiar with arcseconds, but after all, it *is* rocket science ;-).)

For JHelioviewer, I would tend towards option b).

[Jack Ireland (jack-ireland)]

Yes, rocket science indeed!

This feature request arose from some discussions I had talking to some
journalists and others that want to try to push JHV further for the
public. It is pretty clear that an indication of size would be useful
(maybe the unit of 'Rhode Islands' is not the best choice :-). Angular
extent is the safest measurement and indication of scale, but has less
meaning for members of the public. I suppose any which way you look at
it, such a scale tool will require some extra
information/understanding. For example, we don't really make it clear
that all the images are in the plane of the sky, and so all "distances"
are projected.

Even with option (b) - which is my preferred option too -, you may also
have to have an explanation attached that this is an equivalent distance
measurement as if it were made at Sun center. But with option (a),
wouldn't it be simple to update a distance dependent on mouse location?
The size of the bar can stay the same, but the number attached to it
could vary. My original thought was that a "scale" bar would remain at
one position in the viewer window. It would only be there to indicate a
scale, not as a tool that can be dragged around to measure something.

Jack

On 02/02/2011 09:27 AM, Daniel Mueller wrote:
> Hi Jack,
>
> This would definitely be a nice functionality. However, one has to keep
> in mind that our data is not map-projected and the spatial scale varies
> significantly from the center of the disk to the limb.
>
> At least for JHelioviewer, I would think that one would either
>
> a) have to put in quite a bit of effort and make the displayed scale bar
> dependent on a given position on the Sun (e.g. mouse pointer position or
> the location of the scale bar itself)
>
> b) Display the scale as an angular scale, and optionally add an
> conversion to a spatial scale at Sun center. (I am fully aware that not
> everyone is familiar with arcseconds, but after all, it *is* rocket
> science ;-).)
>
> For JHelioviewer, I would tend towards option b).
>