Calculate BMI

[vholer]

Garmin Connect web doesn't show additional metrics, only weight and Garmin calculated BMI. This is caused by very poor weight scale type detection just by available metrics. There are 3 types of view: base, Atlas scale, Tanita scale. Unfortunately, the Atlas scale view (showing the additional metrics) is detected only by presence of calculated BMI, the Tanita scale by presence of visceral fat. If any of these metrics are missing, it fallbacks to base view (just weight + Garmin calculated BMI).

To show additional metrics from Withings, it's necessary to fake Atlas scale by computing the BMI on import. This PR reads user's height from Withings, calculates the BMI and puts it into the FIT. I have to admit that I haven't found the BMI attribute in the offical FIT specification, so it was discovered by experiment.

It happens only on Garmin Connect Web:

The Garmin Connect mobile doesn't suffer of this problem:

Here is the Garmin Connect JavaScript code, which detects weight type by available metrics:

https://connect.garmin.com/modern/main/js/pages/weight/WeightPageView.js?bust=4.15.1.0

        getSelectWeightType: function() {
            return this.checkTanitaDataExist() ? C.TANITA : this.checkAtlasDataExist() ? C.ATLAS : C.OTHER
        },
        checkTanitaDataExist: function() {
            return t.find(this.weights.weightDataList, function(e) {
                return e.visceralFat
            })
        },
        checkAtlasDataExist: function() {
            return t.find(this.weights.weightDataList, function(e) {
                return e.bmi
            })
        },

and, here we can see most metrics is hidden for non-Tanita or non-Atlas scales:

           r && this.$("#directBMIClickedTableRow").html(r);
            if (e === C.TANITA || e === C.ATLAS) {
                var s = this.weightChartView.getSelectBodyFat();
                s != "--" && (s = i.personalizeWeightWithoutConvert(s));
                var o = this.weightChartView.getSelectBodyWater();
                o != "--" && (o = i.personalizeWeightWithoutConvert(o));
                var u = this.weightChartView.getSelectBoneMass();
                u != "--" && (u = this.convertToWeightString(u));
...
            } else
                this.$(".js-body-fat-unit").hide(),
                this.$(".js-body-water-unit").hide(),
                this.$(".js-bone-mass-unit").hide(),

With provided patch and calculated BMI, the view is switched to show additional (Atlas scale) metrics:

[nurps]

Nice, I'm going to test that. :)

[nurps]

Btw on the topic of calculating stuff: Is it possible to calculate the other missing values for people with scales that only do body-fat and weight?

[vholer]

Some of the metrics could be probably calculated, but not much of them. That's why you buy a more expensive scale doing a body (bioelectrical impedance) analysis.

E.g., body fat https://en.wikipedia.org/wiki/Body_fat_percentage calculated from BMI:

• my scale tells 13.3 kg (17.9 %)
• formulas from Wikipedia tells 20.4 % or 21.6 %

I think it makes sense to compute additional metrics which can be reliably calculated base on provided data, but from just weight, heigh and age you can only guess...

Anyway, this PR is more a workaround for crappy Garmin Connect web. I would handle the additional metrics separately ;) Thanks.

[nurps]

Well the Withings WS-50 only measures body-fat. Replacing it with the newer Withings scales doesn't really make sense for me, was just an idea.

[nurps]

Nice it worked (just missing the water, bone and muscle my scale does not record), I can even see my full bodyfat graph dating back when I started measuring.

Only the BMI graph just starts with todays sync, is there a way to sync that for the older entries?

[vholer]

From config.ini delete the line with last_sync=. If you start the script now, it should synchronize all data from Withings again. Obviously, now with calculated BMI.

[magnific0]

@vholer This is really great stuff. Thanks for the code and very detailed PR! Unfortunately, I didn't have time yet to properly test this feature. However, @nurps comments indicate the code works as expected. So I'm going to go ahead with the merge.

Thanks again for all your efforts!