improve

Author: digoal

201810/20181011_01.md

@@ -138,13 +138,29 @@ select *,
 from tt order by c1 <-> ?1 limit xx;  
 ```  
 
+## Euclidean distance , Taxicab distance , Chebyshev distance
+Euclidean distance  
+![pic](20181011_01_pic_002.png)   
+  
+Taxicab distance  
+![pic](20181011_01_pic_003.png)  
+  
+Chebyshev distance  
+![pic](20181011_01_pic_004.png)  
+  
 ## 参考  
 https://www.postgresql.org/docs/devel/static/cube.html  
 
 https://github.com/postgrespro/imgsmlr  
 
 https://github.com/eulerto/pg_similarity  
 
+https://en.wikipedia.org/wiki/Euclidean_distance  
+  
+https://en.wikipedia.org/wiki/Chebyshev_distance  
+  
+https://en.wikipedia.org/wiki/Taxicab_geometry  
+  
 [《PostgreSQL 相似搜索插件介绍大汇总 (cube,rum,pg_trgm,smlar,imgsmlr,pg_similarity) (rum,gin,gist)》](../201809/20180904_01.md)    
 
 [《PostgreSQL 11 相似图像搜索插件 imgsmlr 性能测试与优化 3 - citus 8机128shard (4亿图像)》](../201809/20180904_04.md)