How to implement a geodesic option for the Scale Bar add-in in OpenLayers 2?

Question

I am using the Scale Bar Add-in from OpenLayers 2 and it doesn't have a geodesic option.

I know that the Scale Line has a geodesic option, but considering that the Scale Bar has a wider variety of options, it would be nice to introduce he geodesic option in this one too.

Could anyone help me with this? How could I introduce a geodesic option in the Scale Bar Add-in?

Thank you

Answer 1

I think I solved it.

First of all, I added a geodesic option, so the user can choose if he wantss the geodesic measures or not.

Second, I created this function (based on the ScaleLine):

getGeodesicRatio: function() {
    var res = this.map.getResolution();
    if (!res) {
        return;
    }

    var curMapUnits = this.map.getUnits();
    var inches = OpenLayers.INCHES_PER_UNIT;

    // convert maxWidth to map units
    var maxSizeData = this.maxWidth * res * inches[curMapUnits];
    var geodesicRatio = 1;
    if(this.geodesic) {
        var maxSizeGeodesic = (this.map.getGeodesicPixelSize().w ||
            0.000001) * this.maxWidth;
        var maxSizeKilometers = maxSizeData / inches["km"];
        geodesicRatio = maxSizeGeodesic / maxSizeKilometers;
    }
    return geodesicRatio;
},

Third, I inserted the geodesic ratio in other functions:

"getComp"
var ppdu = OpenLayers.DOTS_PER_INCH * system.inches[unitIndex]
    / this.getGeodesicRatio() / this.scale;

"setSubPros"
var ppdu = OpenLayers.DOTS_PER_INCH * system.inches[unitIndex]
    / this.getGeodesicRatio() / this.scale;

I hope this is useful.