But they won't be the level curves of a function for which this is the gradient.
但它们不一定是，某个以该向量场为梯度的函数的等值线。
To model the ground with the correct heights we used the level curves drawn in the reference drawing.
为了给地面模型设置合适的高度，我们使用从参考图提取的等位曲线。
OK, so that's where we use, actually, the labels on the level curves that tell us whether things are going up or down.
这就是用标记在等高线的地方，这些标记将告诉我们，到底是在上升还是下降。
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