Bug 96871

Created attachment 121693 [details]
XY chart with Y-axis auto log scale

Description: ScaleAutomatism::calculateExplicitIncrementAndScaleForLogarithmic function expands Y-axis auto log scale to B^0 (=1) in almost all cases. On a log scale, "1" has no special meaning: it is not the origin, like "0" is on a linear scale.
See http://opengrok.libreoffice.org/xref/core/chart2/source/view/axes/ScaleAutomatism.cxx#calculateExplicitIncrementAndScaleForLogarithmic
step 2, more specifically
http://opengrok.libreoffice.org/xref/core/chart2/source/view/axes/ScaleAutomatism.cxx#362
/*  If minimum is less than 5 (i.e. original source values less than
    B^5, B being the base of the scaling), or if minimum and maximum
    are in different increment intervals (means, if minimum and maximum
    are not both in the range [B^n,B^(n+1)] for a whole number n), set
    minimum to 0, which results in B^0=1 on the axis. */

Steps to reproduce:
1. Create XY data with Y values between 10^4 and 10^6
2. Create XY chart with Y-axis auto log scale or open attached document

Actual behavior:
Y-axis starts from 1, which creates an empty space between 1 and 10^4, that is 2/3 of chart area.

Expected behavior:
Y-axis should start from 10^4