Line simplification is not only one of the most classic problems but also an important content in cartographic generalization.Most custom line simplification methods focus on the vertexes compression of line features.In cartographic generalization

line simplification is a process of deleting subordinate bends and preserving major bends.Therefore

a new line simplified method based on bend units is proposed. Line features are simplified by the processes of curve bends division and bends deletion.First

after analyzing the characteristics of the oblique-dividing-curve method

the double-oblique-dividing-curve method is proposed to cover the shortage of the former.Bends divided by this method are more accurate and complete.Second

the relationships of bends divided by the double-oblique-dividing-curve method are detected.All bends are classified into three types according to the relationships detected before.In addition

line features are divided into two types of bend-groups

which are distinguished according to different types of bends.Third

different bend deletion methods are used in different types of bend-groups to simplify curve bends gradually and to avoid simplifying excessively.Finally

processes of bend division

relationship detection

and bend deletion are not repeated until all bends divided by the double-oblique-dividing-curve method can be distinguished in the simplified scale.Line features are simplified progressively to reach the visual requirements of the target scale. Line features of hydrographic net someplace at the scale of 1:250 000 are used in the following three experiments.In the first experiment

16 line features and part rivers of the hydrographic net are divided into several bends used the double-oblique-dividing-curve method and the oblique-dividing-curve method.Apparently

each bend divided by the double-oblique-dividing-curve method is more suitable for cognition.The result of the double-oblique-dividing-curve method is more completed than the oblique-dividing-curve method because of avoiding bends omission of the oblique-dividing-curve method.In the second experiment

these 16 line features

at the scale of 1:250 000

are simplified to the scale of 1:500 000

1:1 000 000

and 1:2 000 000 used D-P method

the simplification method based on three-element-bend group

and the proposed method.In terms of the cognitive level

the geometric level and the geographical level

each simplification result used the proposed method of the three target scales is more perfect than the other simplification results used in the other two methods of the same target scale.Moreover

the number of test line features are extended in the third experiment.The hydrographic net

with 965 line features in various shapes

at the scale of 1:250 000

is simplified to the scale of 1:500 000

1:1 000 000

and 1:2 000 000 used the same method as the second experiment.In addition

the location error of each simplified line feature is calculated to evaluate the simplification in quantification

which is used to measure the average displacement resulting from the simplification method.To show clarity

the mean value

the weighted value

and the median value are counted from all location errors of line features in the result

which is simplified to one of the three target scales by one of the three simplification methods.Mean values

weighted values

and median values of results simplified by the proposed method are smaller than the other results simplified by the other two methods at all the three target scales. Curve bends divided by the double-oblique-dividing-curve method is more complete and more accurate according to cognition.Line simplified method based on the double-oblique-dividing-curve method is suitable to the process of manual simplification and cognition.Additionally

it has some advantages in preserving the similarity of geometric features and the integrity of geographic features.Although the proposed simplification method is suitable to simplify line features of various shapes.The proposed method has a significant advantage in simplifying complicated line features

which are composed of numerous crowded bends.Importantly

the proposed simplification method based on the double-oblique-dividing-curve method is suitable for practical simplification of cartographic generalization.