首先我们来看投影的基本定义和规律。
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/b3b7d0a20cf431adee0b36474636acaf2fdd98f6?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
如上图,根据机械制图定义:
主视图——反映物体上、下,左、右的位置关系,反映物体的高度和长度;
俯视图——反映物体前、后,左、右的位置关系,反映物体的宽度和长度;
左视图——反映物体上、下,前、后的位置关系,反映物体的高度和宽度。
最后,投影规律的口诀:长对正,高平齐,宽相等。
第1题解法:
首先,作45°的辅助线,补齐A点投影辅助线。
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/377adab44aed2e733655f5528a01a18b87d6fa14?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
然后,根据A点与B点关系,作出B点投影线,交点即投影点。
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/060828381f30e9247014ef4f41086e061d95f718?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
最后,同样的方式,作出C、D点的投影点,( )表示两个点重合。
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/38dbb6fd5266d01683fced569a2bd40734fa35e2?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
第3题就更简单了,如下图,红色部分为做题补充。
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/3b292df5e0fe9925ff29152e39a85edf8db171a2?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)