[Patch] getAreaText corrupts some area values

[Cobra]

Working with the Measurement plugin I noticed that some areas are displayed as 0.00km². This affects any area >1000m² and <10000m². Areas between 10000m² and 99999m² are displayed with very little precision.

This is caused by some bogous comparison using the same logic for both distance and area, switching units at 1000: source:josm/trunk/src/org/openstreetmap/josm/gui/NavigatableComponent.java#L1280​
I've created a simple patch fixing this issue by using a proper area comparison.

area    | current  | new
1       | 1.00 m²  | 1.00 m²
10      | 10.0 m²  | 10.0 m²
100     | 100.0 m² | 100.0 m²
1000    | 0.00 km² | 1000.0 m²
10000   | 0.01 km² | 10000.0 m²
100000  | 0.10 km² | 100000.0 m²
1000000 | 1.00 km² | 1.00 km²

I'm not completely sure about the behaviour for larger values. Maybe we could drop the decimals for values >= 10000m² or use km² for values >=100000m² (->0.10 km²), limiting the length of the resulting string.

[Don-vip]

Thanks for the patch :)

[Don-vip]

In 5870/josm:

fix #8610 - Wrong display of areas (based on patch by Cobra)

[Preferred]

The current code has an issue with order of operations. a > bValue*bValue / aValue*aValue works for metric since aValue is 1 and thus order doesn't end up mattering. When it is set to Imperial and aValue is 0.3048, it causes undesired results because the divide occurs before the square. This turns the equation into a > bValue *bValue which is not what was intended.

I am attaching a patch that should fix the order of operations issue. Also, I added the custom area unit for the Imperial system, acre, abbreviated ac. I find that I only care about the custom area unit and do not want to see square ft for values less than an acre and square miles for values greater than 640 acres (1 sq mi). I am including a custom attribute to specify to only use the custom area unit named system_of_measurement.use_only_custom_area_unit. It should compliment and not conflict with the system_of_measurement.use_only_lower_unit since that setting is for distance and area.

[Preferred]

Version 2 cleaning up whitespace and adding 1 change

[Don-vip]

In 5952/josm:

fix #8610 - wrong area computation, new preference system_of_measurement.use_only_custom_area_unit(patch by Preferred)