二底图是底图的副本,它是不用描图的方法,在光面薄膜上涂一层薄薄的感光层,用底图进行晒象,经过烤版,暴光、显影、染色和固膜以后,就能得出具有较高遮光力的黑色线条二底图。这种图可以代替底图进行复晒工作,从而减少了描图工作量,延长了矿图的使用寿命。在日常描绘薄膜图工作中,一张50×50厘米的地形图,由一个比较熟练的描图员来描绘,一般需描13～18天左右,但 The bottom of the two is a copy of the bottom map, it is not the method of tracing, the smooth film coated with a thin layer of photosensitive layer, with the base image of the sun, after baking, exposure, development, staining and solid film later , You can come to a black with a higher shading power two at the end of the map. This kind of map can replace the base map for the sun drying work, thus reducing the tracing workload and prolonging the service life of the mine map. In the daily work of filming a map, a 50 × 50-centimeter topographic map, depicted by a more skilled tracer, typically takes between 13 and 18 days, but