# A Method for Extracting Building Information from Remote Sensing Images Based on Deep Learning

Authors: Lianying Li; Xi Chen; Lianchao Li
Journal: Computational Intelligence and Neuroscience
 (2022)

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## Abstract

Semantic segmentation of remote sensing images is an important issue in remote sensing tasks. Existing algorithms can extract information more accurately, but it is difficult to capture the contours of objects and further reveal the interaction information between different objects in the image. Therefore, a deep learning-based method for extracting building information from remote sensing images is proposed. First, the deep learning semantic segmentation model DeepLabv3+ and Mixconv2d are combined, and convolution kernels of different sizes are used for feature recognition. Then, the regularization method based on Rdrop Loss improves the accuracy and efficiency of contour capture for objects of different resolutions, and at the same time improves the consistency of dataset fitting. Finally, the proposed remote sensing image information extraction method is verified based on the self-built dataset. The experimental results show that the proposed algorithm can effectively improve the algorithm efficiency and result accuracy, and has good segmentation performance.


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## Body

## 1. Introduction

Remote sensing images can quickly obtain a wide range of building information data and can be widely used in the monitoring of building surface conditions, as well as in urban and rural layout planning and other fields. However, due to the inevitable influence of spatial resolution, spectral resolution, radiometric resolution, and other factors in the process of remote sensing image acquisition, the data volume of remote sensing images is huge and the types are diverse, and it is necessary to extract the image features quickly and accurately [1–3]. Therefore, designing a high-precision and high-efficiency information extraction method for remote sensing images of buildings has become one of the core tasks of computer vision.The current state-of-the-art DeepLabv3+ algorithm combines the encoder-decoder framework and hole space pyramid pooling, which reduces the amount of computation and improves the accuracy of segmentation [4–6]. Reference [7] uses the DeepLabv3+ algorithm to conduct research in the field of fire detection and explores the performance balance method of Dice and Tversky loss functions in the DeepLabv3+ algorithm by training the entire data set containing RGB and infrared images. However, there are few data points in the fire RGB image, and this method cannot meet the requirements of remote sensing image fitting speed. Reference [8] used convolutional neural networks and semantic segmentation to provide the location and scale of fires for forest fire warning. The study shows that the complexity of the DeepLabv3+ algorithm in terms of shape, texture, color, and intensity is difficult to segment correctly. Reference [9] uses deep convolutional neural networks to automatically generate training datasets in heterogeneous and cluttered backgrounds. However, the algorithm has a slow fitting speed, inaccurate segmentation of edge objects, inconsistency within large-scale object segmentation and defects such as holes. Based on the above-given problems, aiming at the DeepLabv3+ algorithm widely used in the field of remote sensing images, this paper proposes a deep learning algorithm that can improve the fitting rate and segmentation efficiency. Aiming at the low fitting speed of the original model, the Rdrop Loss regularization method is used to forward the samples twice. The symmetric Kullback-Leibler(KL) divergence loss of these two distributions is added to the original cross-entropy loss to achieve joint backpropagation and parameter update [10, 11]. By minimizing the divergence loss, the expressive ability and generalization ability of remote sensing image segmentation are enhanced [12]. Aiming at the problem of low segmentation accuracy in the original model, this paper takes advantage of multiscale convolution kernels and mixes multiple convolution kernels in one convolution operation. A large-sized convolution kernel is used to obtain high-resolution remote sensing image pattern information, and a small-sized convolution kernel is used to capture low-resolution pattern information to compensate for the boundary segmentation accuracy problem of DeepLabv3+ in remote sensing image tasks [13, 14].Aiming at the problem of low segmentation accuracy and efficiency in segmentation tasks caused by the dense arrangement of targets in remote sensing images and the large size variation of similar targets, this paper proposes the Super-DeepLabv3+ algorithm from the convolution method and the regularization method. Compared with the traditional algorithm, the innovation of the proposed method lies as follows:(1)
By minimizing the loss function composed of KL divergence, the proposed algorithm achieves higher scores for the target class than for nontarget classes under different dropouts. Therefore, it has better robustness in remote sensing image scenes with a large amount of data.(2)
By combining different sizes of convolution kernels, the proposed Mixconv2d method acts as a simple replacement for ordinary depthwise convolutions. Different size kernels can be used to learn information of different scales, which further improves the accuracy and efficiency of the algorithm.Based on the remote sensing image segmentation task, this paper proposes a new deep learning algorithm Super-DeepLabv3+. The recent research progress in the field of remote sensing image classification and segmentation is investigated, and the achievements and defects of mainstream algorithms are summarized. We further propose a novel semantic segmentation algorithm that adopts DeepLabv3+ as encoder and decoder modules. Convolution kernels of different sizes are used to arbitrarily control the resolution of the extracted encoder features, and the Rdrop Loss method is used to improve the robustness of the model. The validity of the Super-DeepLabv3+ algorithm is verified through experiments. The experimental results show that this algorithm has better performance than the DeepLabv3+ algorithm and has great potential in segmentation tasks.Section2 of this paper describes related work on building information extraction. Section 3 introduces the method and innovation of this paper. Section 4 compares the proposed method with other methods and analyzes the results. Section 5 is the conclusion of the paper.


## 2. Related Work

Buildings in a broad sense refer to all artificially constructed structures, including structures and houses. There are many classification standards for buildings, which can usually be classified according to the nature of use. In addition, buildings are classified based on building height, building structure, etc. Generally, the basic image features of buildings in remote sensing images are mainly manifested in the following four aspects. (1) Spectral features. (2) Shape features. (3) Texture Features. (4) Contextual Features.Based on the above-given features, building information can be extracted from remote sensing images. In order to meet the needs of military detection, urban planning, statistical census, disaster emergency assessment, and other fields in the basic geographic information system database.


### 2.1. Traditional Remote Sensing Image Information Extraction Method

In order to accurately extract building objects, traditional methods can be divided into three categories according to the specific technology used: (1) Methods based on traditional edge/line detection techniques. (2) Methods based on the curve propagation class techniques. (3) Methods based on segmentation class techniques.The methods based on traditional edge detection technology generally form a closed contour by gradually combining edges or straight line segments by extracting edge or straight line segment information in the image. And, then use the prior information such as building shape to realize the extraction of the target contour of the complete closed building. For example, Reference [15] uses the canny edge detection method to extract and segment the selected area of the mouza map image system to realize the precise planning of the area. However, this method cannot robustly handle regions of interest (ROI) with different contrast or shadow conditions such as weak texture, noise, or occlusion. Therefore performance is limited by Gaussian similarity and continuity related measures. Reference [16] combined the Shi_Tomasi corner detection algorithm and scale-invariant feature transformation to realize the registration of remote sensing images before and after earthquakes. However, this method relies on the edge of the building, and it is difficult to realize the joint application of global and local multi-scale information, which affects the extraction accuracy of remote sensing images.For traditional boundary detection/extraction methods, there are always many discontinuous edge segments. Some of these should actually be connected to each other to form a continuous boundary of meaningful objects. For this reason, based on the traditional edge detection results, additional edge linking operations are often required to improve the accuracy and reliability of building detection, that is, methods based on curve propagation techniques. For example, Reference [17] uses an active contour model to verify the depiction of building contours in aerial images. But this method is limited by the extraction of building prior information. Reference [18] proposes a low-rank minimization problem and estimates fused features in a lower-dimensional subspace using a novel iterative algorithm based on a multiplier-based alternative direction approach. While these methods are able to give closed contours, they are sensitive to initially detected edges, and there is no guarantee that a globally optimal boundary can be found. Obviously, since this method cannot fully utilize the global information, its application in building object extraction has certain limitations.Considering that the first two methods cannot fully utilize global and local building prior information, segmentation techniques have been widely used in building object extraction through object-oriented processing. Reference [19] used training data to obtain the optimal scale parameters for multiresolution segmentation and then segmented remote sensing images. Then perform multifeature extraction on each object obtained by segmentation. Finally, the building object extraction is realized by classification. Such methods rely heavily on initial segmentation and are difficult to extract objects from complex buildings and dense building areas.


### 2.2. Remote Sensing Image Information Extraction Method Based on Deep Learning

Due to the complex process, low degree of automation, and limited promotion ability of traditional remote sensing image information extraction methods. Existing studies have used deep learning techniques to extract building objects. Deep learning has two characteristics of feature learning and deep structure, which is conducive to the improvement of remote sensing image classification accuracy. Feature learning can automatically learn the required high-level feature representation from massive data according to different applications, and can better express the inherent information of the data. Deep structures usually have multiple layers of hidden layer nodes and contain more nonlinear transformations, which greatly enhances the ability to fit complex models. Deep learning classification algorithms in remote sensing images can be divided into supervised learning and unsupervised learning. Typical application methods include Deep Belief Nets (DBN), Convolutional Neural Network (CNN), Sparse Auto-Encoder (SAE), and so on.DBN is an improved network of restricted Boltzmann machine (RBM), which belongs to unsupervised learning. Reference [20] introduced local receptive field and weight sharing into Deep Boltzmann Machine (DBM), and established a local-global DBM. However, this method requires more computing resources and increases the corresponding management cost. Reference [21] improves spectral-spatial classification of HSI by extracting meaningful features to learn and distinguish representations of hyperspectral samples in hidden layers. However, the inherent shortcomings of unsupervised learning make it possible that the results pursue local optimality and are sensitive to noise.The essence of CNN is the mapping relationship between input and output. Before learning, there is no explicit mathematical model between input and output. CNN builds a model by training a convolutional network by learning a large number of mappings between input and output. Reference [22] proposed a multiscale CNN (MCNN) framework to solve the multiscale problem of optical remote sensing images. Trained simultaneously by a dual-branch structure of a fixed-scale network (F-net) and a variable-scale network (V-net). However, the gradient descent algorithm used can easily make the training result converge to the local minimum rather than the global minimum while ignoring the correlation between the local and the whole. Reference [23] proposed a feature learning method named Deep Lab Dilated Convolutional Neural Network (DL-DCNN) based on automatic semantic segmentation to improve the accuracy of detecting images. However, the accuracy of the results of this method is limited by the precision and parameter selection of preprocessing and requires higher computational performance.SAE is an improved auto-encoder (AE). SAE is formed by the layer-by-layer superposition of AE. It obtains concise and effective features by encoding and decoding the feature expression of the observation data, and deeply captures the rules hidden in the data. In order to make full use of implicit information such as data categories and patterns, it is also necessary to supervised fine-tuning of its model parameters. For example, Reference [24] proposes a spectral-spatial method for hyperspectral image classification by modifying the traditional auto-encoder based on the Majorization Minimization (MM) technique. However, because this method extracts multiscale features, the parameters will have a greater impact on the accuracy of target detection results. Reference [25] proposed a deep neural network based on SAE and semisupervised to estimate the soft labels of a large amount of existing unlabeled data and then used the soft labels to improve the model training. However, this method is restricted by the environment configuration, which reduces its generalization and generalization ability.To sum up, there are still many problems in the application of typical target extraction methods in remote sensing images. For example, the mining of spatial relationships and the computational complexity are high. In practical applications, it is necessary to extract from massive high-resolution images, and the use of spectral information is insufficient. Compared with natural image target extraction in other fields, the extraction of building target prior information runs through all key links of building target extraction, and the available information is diverse. How to effectively select relevant information for building target extraction is still a scientific issue that needs to be deeply explored.


## 2.1. Traditional Remote Sensing Image Information Extraction Method

In order to accurately extract building objects, traditional methods can be divided into three categories according to the specific technology used: (1) Methods based on traditional edge/line detection techniques. (2) Methods based on the curve propagation class techniques. (3) Methods based on segmentation class techniques.The methods based on traditional edge detection technology generally form a closed contour by gradually combining edges or straight line segments by extracting edge or straight line segment information in the image. And, then use the prior information such as building shape to realize the extraction of the target contour of the complete closed building. For example, Reference [15] uses the canny edge detection method to extract and segment the selected area of the mouza map image system to realize the precise planning of the area. However, this method cannot robustly handle regions of interest (ROI) with different contrast or shadow conditions such as weak texture, noise, or occlusion. Therefore performance is limited by Gaussian similarity and continuity related measures. Reference [16] combined the Shi_Tomasi corner detection algorithm and scale-invariant feature transformation to realize the registration of remote sensing images before and after earthquakes. However, this method relies on the edge of the building, and it is difficult to realize the joint application of global and local multi-scale information, which affects the extraction accuracy of remote sensing images.For traditional boundary detection/extraction methods, there are always many discontinuous edge segments. Some of these should actually be connected to each other to form a continuous boundary of meaningful objects. For this reason, based on the traditional edge detection results, additional edge linking operations are often required to improve the accuracy and reliability of building detection, that is, methods based on curve propagation techniques. For example, Reference [17] uses an active contour model to verify the depiction of building contours in aerial images. But this method is limited by the extraction of building prior information. Reference [18] proposes a low-rank minimization problem and estimates fused features in a lower-dimensional subspace using a novel iterative algorithm based on a multiplier-based alternative direction approach. While these methods are able to give closed contours, they are sensitive to initially detected edges, and there is no guarantee that a globally optimal boundary can be found. Obviously, since this method cannot fully utilize the global information, its application in building object extraction has certain limitations.Considering that the first two methods cannot fully utilize global and local building prior information, segmentation techniques have been widely used in building object extraction through object-oriented processing. Reference [19] used training data to obtain the optimal scale parameters for multiresolution segmentation and then segmented remote sensing images. Then perform multifeature extraction on each object obtained by segmentation. Finally, the building object extraction is realized by classification. Such methods rely heavily on initial segmentation and are difficult to extract objects from complex buildings and dense building areas.


## 2.2. Remote Sensing Image Information Extraction Method Based on Deep Learning

Due to the complex process, low degree of automation, and limited promotion ability of traditional remote sensing image information extraction methods. Existing studies have used deep learning techniques to extract building objects. Deep learning has two characteristics of feature learning and deep structure, which is conducive to the improvement of remote sensing image classification accuracy. Feature learning can automatically learn the required high-level feature representation from massive data according to different applications, and can better express the inherent information of the data. Deep structures usually have multiple layers of hidden layer nodes and contain more nonlinear transformations, which greatly enhances the ability to fit complex models. Deep learning classification algorithms in remote sensing images can be divided into supervised learning and unsupervised learning. Typical application methods include Deep Belief Nets (DBN), Convolutional Neural Network (CNN), Sparse Auto-Encoder (SAE), and so on.DBN is an improved network of restricted Boltzmann machine (RBM), which belongs to unsupervised learning. Reference [20] introduced local receptive field and weight sharing into Deep Boltzmann Machine (DBM), and established a local-global DBM. However, this method requires more computing resources and increases the corresponding management cost. Reference [21] improves spectral-spatial classification of HSI by extracting meaningful features to learn and distinguish representations of hyperspectral samples in hidden layers. However, the inherent shortcomings of unsupervised learning make it possible that the results pursue local optimality and are sensitive to noise.The essence of CNN is the mapping relationship between input and output. Before learning, there is no explicit mathematical model between input and output. CNN builds a model by training a convolutional network by learning a large number of mappings between input and output. Reference [22] proposed a multiscale CNN (MCNN) framework to solve the multiscale problem of optical remote sensing images. Trained simultaneously by a dual-branch structure of a fixed-scale network (F-net) and a variable-scale network (V-net). However, the gradient descent algorithm used can easily make the training result converge to the local minimum rather than the global minimum while ignoring the correlation between the local and the whole. Reference [23] proposed a feature learning method named Deep Lab Dilated Convolutional Neural Network (DL-DCNN) based on automatic semantic segmentation to improve the accuracy of detecting images. However, the accuracy of the results of this method is limited by the precision and parameter selection of preprocessing and requires higher computational performance.SAE is an improved auto-encoder (AE). SAE is formed by the layer-by-layer superposition of AE. It obtains concise and effective features by encoding and decoding the feature expression of the observation data, and deeply captures the rules hidden in the data. In order to make full use of implicit information such as data categories and patterns, it is also necessary to supervised fine-tuning of its model parameters. For example, Reference [24] proposes a spectral-spatial method for hyperspectral image classification by modifying the traditional auto-encoder based on the Majorization Minimization (MM) technique. However, because this method extracts multiscale features, the parameters will have a greater impact on the accuracy of target detection results. Reference [25] proposed a deep neural network based on SAE and semisupervised to estimate the soft labels of a large amount of existing unlabeled data and then used the soft labels to improve the model training. However, this method is restricted by the environment configuration, which reduces its generalization and generalization ability.To sum up, there are still many problems in the application of typical target extraction methods in remote sensing images. For example, the mining of spatial relationships and the computational complexity are high. In practical applications, it is necessary to extract from massive high-resolution images, and the use of spectral information is insufficient. Compared with natural image target extraction in other fields, the extraction of building target prior information runs through all key links of building target extraction, and the available information is diverse. How to effectively select relevant information for building target extraction is still a scientific issue that needs to be deeply explored.


## 3. Methods

This chapter proposes a CNN model that can improve the accuracy and efficiency of remote sensing image segmentation tasks. The method is based on the DeepLabv3+ algorithm and uses the Rdrop Loss method to enhance the consistency of training and inference models, making it suitable for remote sensing image segmentation tasks. The improved model further employs Mixconv2d convolutions to enable the extraction of features computed by deep convolutional neural networks at arbitrary resolutions. On this basis, Super-DeepLabv3+ also detects convolution features on multiple scales by applying convolution kernel functions with different sizes and further realizes batch extraction of remote sensing image features.


### 3.1. Mixconv2d

The main idea of Mixconv2d is to fuse multiple convolution kernels with different sizes in one depthwise convolution operation, which greatly reduces the difficulty of capturing different types of features from the input image.The Mixconv2d feature map is shown in equation (1). Here, s is the kernel size, c is the input channel size, and n is the channel multiplier.(1)Tx,y,z=∑−s/2≤a≤s/2,−s/2≤b≤s/2Ex+a,y+b,z/n⋅Ra,b,z,∀z=1,…,n⋅c.Unlike general depthwise convolution, Mixconv2d divides the channels into groups and defines kernels of different sizes for each group. For example,l sets of virtual tensors E∧g,k,c1,⋯,E∧g,k,cl, the height g of the tensors is consistent with the width k, and their total channel size is equal to the original input tensors. Then, the virtual output corresponding to the pth virtual input vector and the kernel can be obtained as shown in the following formula.(2)T∧x,y,z=∑−sp/2≤a≤sp/2,−sp/2≤b≤sp/2E∧x+a,y+b,z/np⋅R∧a,b,zp,∀z=1,…,n⋅cp.The final output tensor is the concatenation of all formulas (2), T∧x,y,z11,…,T∧x,y,zpp is shown in the following formula:(3)Tx,y,z0=ConcatT∧x,y,z1,…,T∧x,y,zpp.Mixconv2d can be implemented as a single operation and optimized using group convolutions. The TensorFlow code of Mixconv2d is shown in Algorithm1. As shown in the figure, Mixconv2d can be seen as a simple replacement for ordinary depthwise convolution.Algorithm 1: A demo of TensorFlow Mixconv2d.
def Mixconv2d(x, filters, args):#patameter define:#x: the features of input tensor;#filters: the list of specific filters’ shape;#args: reference variableL = len(fliters)#groups of number.y = [ ]forxi, fiin zip (tf.split(x, G, axis = −i), fliters):y.append(tf.nn.deptwise_conv2d(xi, fi, args))return tf.concat(y, axis = −1)MixConv has a variety of design options. The optimal design can be made from a single input tensor using different types of kernel sizes, kernel sizes per group, number of channels per group size, and dilated convolutions.


### 3.2. RDrop Loss

Dropout performs implicit ensemble by simply dropping a certain percentage of hidden units from the neural network during training. However, this method has certain risks. Research has shown that the Dropout model has obvious inconsistencies in the training and inference stages. R-Drop introduces a simple consistency training strategy based on Dropout to regularize Dropout so that the outputs of its sub-models are consistent. That is, for each training sample, R-Drop minimizes the bidirectional KL divergence between the output distributions of the two sub-models that drop samples. R-Drop regularizes the output of two sub-models that are randomly sampled from the dropout for each data sample in training. In this way, the inconsistency between the training phase and the inference phase can be mitigated. Compared with the Dropout strategy in traditional neural network training, R-Drop only adds a KL-divergence loss without any structural changes.R-Drop regularization requires a given training datasetE=xj,yjj=1m. The training objective is to learn the model Qzyx. Where m is the number of training samples, xj,yj is the data pair, xj is the input data, and yj is the label. The input data is further regarded as the probability distribution of the mapping function, and the KL divergence between the two distributions Q1 and Q2 is denoted as SKLQ1Q2.The loss function that minimizes the negative log-likelihood given training data is expressed as follows:(4)Lnull=1n∑i=1n−logQzyixi.With a given input, the input signal is fed back to the forward channel of the network twice, and two distributions are predicted by the model,Q1zyixi and Q2zyixi, are obtained. The R-Drop method attempts to regularize model predictions by minimizing the bidirectional KL divergence between these two output distributions for the same sample, namely,(5)LKLi=12EKLQ1zyixiQ2zyixi+EKLQ1zyixiQ2zyixi.The basic negative log-likelihood learning objective using two prequels is(6)LNLLi=−logQ1zyixi−logQ2zyixi.The final training objective is to minimize theLi of the data yixi:(7)Li=LNLLi+β⋅LNLLi=−logQ1zyixi−logQ2zyixi+β2EKLQ1zyixiQ2zyixi+β2EKLQ2zyixiQ1zyixi,where β is the parameter weight assignment.The specific algorithm is shown in Algorithm2.Algorithm 2: Pseudo-code for R-Drop training algorithm routines.
Input: Training data E=xj,yjj=1m:Output: model data z.(1)
Initialize model with parametersz.(2)
while not converged do(3)
randomly sample data pairxj,yj∼L(4)
repeat input data twice and then obtain the output distribution(5)
calculateLNLLi(6)
calculateLKLi(7)
update the model parameters by minimizingLi(8)
end while


### 3.3. Super DeepLabv3+

Super-DeepLabv3+ performs R-Dropout Loss regularization based on Mixconv2d convolution. This method can greatly improve the segmentation accuracy and efficiency of remote sensing images.For remote sensing image segmentation tasks, there are many data points and a large amount of computation. The segmentation algorithm needs to improve the training efficiency as much as possible without losing image features. Using Super-DeepLabv3+ to perform the segmentation task requires building two image network datasets with the same number of sampling points and regularization during the data training process. By composing the minimization training objective based on the negative log-likelihood and the KL divergence as the basis functions, the complete newness of the model and the effect and efficiency of regularization are improved. On this basis, the Mixconv2d convolution is further used to replace the original 3 × 3 depth convolution network. Reduce the number of parameters while maintaining the same accuracy. The algorithm framework of Super-DeepLabv3+ is shown in Figure1.Figure 1
The overall framework of proposed super DeepLabv3+.


## 3.1. Mixconv2d

The main idea of Mixconv2d is to fuse multiple convolution kernels with different sizes in one depthwise convolution operation, which greatly reduces the difficulty of capturing different types of features from the input image.The Mixconv2d feature map is shown in equation (1). Here, s is the kernel size, c is the input channel size, and n is the channel multiplier.(1)Tx,y,z=∑−s/2≤a≤s/2,−s/2≤b≤s/2Ex+a,y+b,z/n⋅Ra,b,z,∀z=1,…,n⋅c.Unlike general depthwise convolution, Mixconv2d divides the channels into groups and defines kernels of different sizes for each group. For example,l sets of virtual tensors E∧g,k,c1,⋯,E∧g,k,cl, the height g of the tensors is consistent with the width k, and their total channel size is equal to the original input tensors. Then, the virtual output corresponding to the pth virtual input vector and the kernel can be obtained as shown in the following formula.(2)T∧x,y,z=∑−sp/2≤a≤sp/2,−sp/2≤b≤sp/2E∧x+a,y+b,z/np⋅R∧a,b,zp,∀z=1,…,n⋅cp.The final output tensor is the concatenation of all formulas (2), T∧x,y,z11,…,T∧x,y,zpp is shown in the following formula:(3)Tx,y,z0=ConcatT∧x,y,z1,…,T∧x,y,zpp.Mixconv2d can be implemented as a single operation and optimized using group convolutions. The TensorFlow code of Mixconv2d is shown in Algorithm1. As shown in the figure, Mixconv2d can be seen as a simple replacement for ordinary depthwise convolution.Algorithm 1: A demo of TensorFlow Mixconv2d.
def Mixconv2d(x, filters, args):#patameter define:#x: the features of input tensor;#filters: the list of specific filters’ shape;#args: reference variableL = len(fliters)#groups of number.y = [ ]forxi, fiin zip (tf.split(x, G, axis = −i), fliters):y.append(tf.nn.deptwise_conv2d(xi, fi, args))return tf.concat(y, axis = −1)MixConv has a variety of design options. The optimal design can be made from a single input tensor using different types of kernel sizes, kernel sizes per group, number of channels per group size, and dilated convolutions.


## 3.2. RDrop Loss

Dropout performs implicit ensemble by simply dropping a certain percentage of hidden units from the neural network during training. However, this method has certain risks. Research has shown that the Dropout model has obvious inconsistencies in the training and inference stages. R-Drop introduces a simple consistency training strategy based on Dropout to regularize Dropout so that the outputs of its sub-models are consistent. That is, for each training sample, R-Drop minimizes the bidirectional KL divergence between the output distributions of the two sub-models that drop samples. R-Drop regularizes the output of two sub-models that are randomly sampled from the dropout for each data sample in training. In this way, the inconsistency between the training phase and the inference phase can be mitigated. Compared with the Dropout strategy in traditional neural network training, R-Drop only adds a KL-divergence loss without any structural changes.R-Drop regularization requires a given training datasetE=xj,yjj=1m. The training objective is to learn the model Qzyx. Where m is the number of training samples, xj,yj is the data pair, xj is the input data, and yj is the label. The input data is further regarded as the probability distribution of the mapping function, and the KL divergence between the two distributions Q1 and Q2 is denoted as SKLQ1Q2.The loss function that minimizes the negative log-likelihood given training data is expressed as follows:(4)Lnull=1n∑i=1n−logQzyixi.With a given input, the input signal is fed back to the forward channel of the network twice, and two distributions are predicted by the model,Q1zyixi and Q2zyixi, are obtained. The R-Drop method attempts to regularize model predictions by minimizing the bidirectional KL divergence between these two output distributions for the same sample, namely,(5)LKLi=12EKLQ1zyixiQ2zyixi+EKLQ1zyixiQ2zyixi.The basic negative log-likelihood learning objective using two prequels is(6)LNLLi=−logQ1zyixi−logQ2zyixi.The final training objective is to minimize theLi of the data yixi:(7)Li=LNLLi+β⋅LNLLi=−logQ1zyixi−logQ2zyixi+β2EKLQ1zyixiQ2zyixi+β2EKLQ2zyixiQ1zyixi,where β is the parameter weight assignment.The specific algorithm is shown in Algorithm2.Algorithm 2: Pseudo-code for R-Drop training algorithm routines.
Input: Training data E=xj,yjj=1m:Output: model data z.(1)
Initialize model with parametersz.(2)
while not converged do(3)
randomly sample data pairxj,yj∼L(4)
repeat input data twice and then obtain the output distribution(5)
calculateLNLLi(6)
calculateLKLi(7)
update the model parameters by minimizingLi(8)
end while


## 3.3. Super DeepLabv3+

Super-DeepLabv3+ performs R-Dropout Loss regularization based on Mixconv2d convolution. This method can greatly improve the segmentation accuracy and efficiency of remote sensing images.For remote sensing image segmentation tasks, there are many data points and a large amount of computation. The segmentation algorithm needs to improve the training efficiency as much as possible without losing image features. Using Super-DeepLabv3+ to perform the segmentation task requires building two image network datasets with the same number of sampling points and regularization during the data training process. By composing the minimization training objective based on the negative log-likelihood and the KL divergence as the basis functions, the complete newness of the model and the effect and efficiency of regularization are improved. On this basis, the Mixconv2d convolution is further used to replace the original 3 × 3 depth convolution network. Reduce the number of parameters while maintaining the same accuracy. The algorithm framework of Super-DeepLabv3+ is shown in Figure1.Figure 1
The overall framework of proposed super DeepLabv3+.


## 4. Experimental Results and Analysis

In order to verify the accuracy and related performance of the algorithm proposed in this paper, the experimental environment and hardware related configuration are shown in Table1.Table 1
Experimental environment.
NameRelated configurationCPUIntel(R) Xeon(R) CPU 6258R × 2RAMDDR4 2400 MHz 256 GBAcceleration libraryCUDA11.1, cudnn8.0.4GPURTX3090 × 4Operating systemUbuntu 16.04Processing softwarePython 3.7, PIL, OpenCVFrameworkPytorch 1.7.0Python version3.7


### 4.1. Network Parameter Settings

Adam optimizer is used during training. The primary parameter is the learning rate, which refers to back-propagating the output error to the network parameters to fit the output of the sample. In essence, the optimization process tends to the optimal solution step by step, but how much error each update parameter utilizes needs to be controlled by a parameter. This parameter is the learning rate Learning rate, and the initial learning rate is set to 0.001. At the same time, the optimal learning rate is not a fixed value, but a variable value that decays with the number of training sessions. That is, in the early stage of training, the learning rate is relatively large, and as the training progresses, the learning rate continues to decrease until the model converges. In the experiment, the median frequency balanced cross-entropy loss function is used to assist training, and the learning rate is attenuated by the Poly decay strategy, and the weight decay is 0.0005. That is, use formula (8) to adjust the learning rate.(8)prepoch=prepoch−11−epochmax_epoch0.9.In the formula,prepoch represents the learning rate of the current epoch, prepoch−1 represents the learning rate of the previous epoch, and max_epoch represents the set maximum epoch. An epoch means that all data is sent to the network, and a process of forward calculation + backpropagation is completed. As the number of epochs increases, so does the number of updates to the weights in the neural network. The curve goes from the initial unfit state to the optimal fitting state, and finally to overfitting. According to the actual verification, the maximum epoch of this experiment is set to 200, and the validation set is used for evaluation after each epoch. If the evaluation index does not improve for 10 consecutive epochs, the training is terminated.


### 4.2. Evaluation Indicators

The experimental evaluation indicators include algorithm efficiency and algorithm accuracy. The performance of the remote sensing image building information extraction algorithm can be relatively comprehensively summarized and described.


#### 4.2.1. Algorithm Efficiency Related Evaluation Index

In terms of algorithm efficiency, the convergence time, inference occupied video memory and inference speed are selected as the evaluation criteria.(1)
The convergence time of the algorithm refers to whether the algorithm can finally find the global optimal solution of the problem, and the time required to find the optimal solution. Therefore, the meaning of fast convergence is that relatively accurate values can be obtained with fewer iterations.(2)
In inference tasks, there are three main parts that occupy GPU memory: model weights, input and output, and intermediate results. Deep learning models are often stacked with layers with similar structures, such as convolutional layers, pooling layers, fully connected layers, and activation function layers. Some layers have parameters. For example, the parameter of the convolutional layer is a high-dimensional convolution kernel, and the parameter of the fully connected layer is a two-dimensional matrix. There are also some layers without parameters, such as activation function layers, pooling layers, etc. Therefore, different model weights are formed. In the forward calculation, the output of the previous layer corresponds to the input of the next layer, and the intermediate results connecting the two adjacent layers also need GPU memory to save. Compared to the model weights and intermediate results, the GPU memory occupied by the input and output is relatively small. At the same time, due to the existence of backpropagation in the training phase, the usage of GPU memory will be more complicated.(3)
In deep learning, inference refers to a forward propagation process of a neural network. That is, the process of feeding input data into a neural network and then getting an output from it. The inference speed is the time from the image input model after preprocessing to the model output result. The inference speed of a model on a specific hardware is not only affected by the amount of computation, but also affected by many factors such as the inventory, hardware characteristics, software implementation, and system environment.


#### 4.2.2. Algorithm Accuracy Related Evaluation Index

In terms of algorithm accuracy, with the ground truth map as a reference, the evaluation index can be used to quantitatively analyze the segmentation results. First, it is assumed that there aren+1 classification categories 0−n in the ground object segmentation dataset, and category 0 represents the background. Using pij to indicate that the true classification label of a certain pixel is i, and the label predicted by the network model is j. When i=j, the prediction is called true positive (TP) if i is a foreground sample, and true negative (TN) if i is a background sample. When i≠j, if i is a foreground sample, the prediction is called a false negative (FN), and if i is a background sample, the prediction is called a false positive (FP). Select the accuracy rate (Acc), class accuracy rate (Acc_class), mean intersection over union (mIoU), and frequency weight intersection over union (FWloU) several evaluation indicators to evaluate the accuracy of the model.Acc represents the proportion of correctly classified pixels in all pixels, and the calculation method is shown in the following equation:(9)Acc=TP+TNTP+TN+FN+FP.Acc_class indicates that for each class, the number of correct predictions for this class/the number of all predictions for this class. Calculate the proportion of correctly classified pixels to all predicted pixels of that class, and then accumulate and average, as shown in the following equation:(10)Accclass=1NTPTP+FP.IoU refers to the ratio of the intersection and union between the true set of each classification category and the correctly classified predicted set, as shown in the following equation:(11)IoU=TPTP+FP+FN=∑i=1Nnii∑i=1Nmi+∑j=1Nnji−nii.Here, mIoU refers to the average of the ratio of the intersection and union between the label value and the correct predicted value of each classification category, as shown in the following formula:(12)mIoU=1NTPTP+FP+FN=1N∑i=1Nnii∑i=1Nmi+∑j=1Nnji−nii.FWIoU is to set weights according to the frequency of occurrence of each class, and the weights are multiplied by the IoU of each class and summed. The formula is as follows:(13)FWIoU=TPTP+FP+FNTP+FNTP+FP+FN=1∑j=1N∑i=1Nnii∑i=1N∑j=1Nniinij∑i=1Nmi+∑j=1Nnji−nii.


### 4.3. Remote Sensing Image Dataset

In order to verify the performance of the Super-DeepLabv3+ model for extracting building information from remote sensing images, a self-built dataset was selected to evaluate the model results. The dataset has a total of 127 images, covering a variety of scenes containing sparse and dense buildings. The number of images in each scene varies from 50 to 60. The horizontal and vertical resolution of each image is 96 dpi. To facilitate training, by randomly splitting between tiles. The dataset is divided into training set, validation set, and test set according to the ratio of 8 : 1 : 1. That is, 104 images are divided into training set, 11 images are divided into a validation set, and 12 images are divided into test set.Usually, the size of remote sensing images is large, and it is difficult to directly input into the model. The remote sensing image needs to be cropped into multiple small-sized subimages, then input into the model for prediction, and then stitched to obtain the final segmentation result. If no measures are taken, stitching marks may occur. The main reason is that the original remote sensing image has been cropped, and the feature information at the edge of the small-size subimage is incomplete, resulting in the loss of some of the above-given information in the small-size subimage. In order to eliminate the stitching traces, the remote sensing images need to be cropped into small-sized subimages by overlapping sliding windows. The prediction results of the small-sized subimages are obtained by the model and then stitched in sequence. It should be noted that the edge regions of the prediction results of small-sized subimages are ignored during stitching. In the experiment, the dataset is cropped into subimages of 256 pixels × 256 pixels according to the sliding window overlap step size of 40 pixels. At the same time, the images of the training set are expanded by scaling, flipping, color transforming, adding noise, and random erasing to improve the generalization ability of the model.


### 4.4. Experimental Results

In the experiment, five semantic segmentation networks were trained on remote sensing feature segmentation datasets, including Unet network model [26], Mix_DeepLabv3+ network model, DeepLabv3+ network model [7], Rdrop_DeepLabv3+ network model, and Super-DeepLabv3+ network model. And, a more comprehensive comparison and reason analysis are carried out on the algorithm execution efficiency and accuracy of the trained model. The segmentation performance of the network model is further intuitively evaluated by data analysis, and its shortcomings are analyzed.


#### 4.4.1. Comparison of the Execution Efficiency of Different Remote Sensing Image Information Extraction Methods

In Table2 shows the comparison of video memory occupied, convergence time and inference speed for each network model training.Table 2
Efficiency comparison of various network models.
Network nameConvergence time (h)Inference occupies video memory (GB)Inference speed (fps)Unet63.320.5Mix_DeepLabv3+84.216.7DeepLabv3+104.317.6Rdrop_DeepLabv3+73.715.1Super DeepLabv3+73.614.8For the model convergence time, from the training results, the Unet network model has the fastest convergence speed, which takes 6 hours. The slowest is the DeepLabv3+ network model, which takes 10 hours to train from start to convergence. Although the five network models have long or short convergence times in a fixed training period, the overall difference is not large. This is because the batch normalization layer is used in the implementation of the network model, which can prevent the gradient from exploding. The mean and standard deviation calculated on the mini-batch are used to dynamically adjust the segmentation of the output of the intermediate layer of the deep convolutional neural network, so that the entire network is more stable in the intermediate output of each layer, thereby accelerating the convergence speed. The learning rate decay strategy used in training enables the network model to avoid the explosion of loss values during the training process, and then achieve convergence.For inference that occupies video memory, when the training batch size and input image size are fixed, a network model with a large number of parameters will occupy more video memory. It can be seen from Table2 that the Unet network model inference occupies 3.3 GB of video memory, and the inference occupies the least video memory. Because the Unet network model uses skip connections between each corresponding layer of the encoder network and the decoder network to perform feature fusion. Therefore, the intermediate feature maps of each stage in the encoder network need to be stored during training. Although this will lead to a larger video memory occupied by inference, the total occupancy is minimal because the number of intermediate feature map channels in Unet is designed to be less. DeepLabv3+ network model inference occupies the largest video memory, which is 4.3 GB. This is because the DeepLabv3+ network model also performs feature fusion with the shallow feature map of the encoder network in the process of restoring the resolution of the feature map, which requires additional storage of the intermediate feature map of the encoder during training.For inference speed, the Super-DeepLabv3+ network model has the fastest inference speed of 14.8 fps. This is because the Super-DeepLabv3+ network model is regularized during data training. On this basis, the Mixconv2d convolution is further used to replace the original deep convolution network, which reduces the number of parameters while ensuring the same accuracy. Compared with other methods, the proposed Super-DeepLabv3+ method significantly improves the efficiency and performance of the algorithm on the basis of ensuring convergence and ensures the effective execution of remote sensing image information extraction.


#### 4.4.2. Comparison of Accuracy of Different Remote Sensing Image Information Extraction Methods

In terms of the accuracy comparison of different remote sensing image information extraction methods, a typical remote sensing building image is taken as an example to compare the performance between the models. Figures2(a)–2(f) are the original images of remote sensing buildings, and the extraction results of building information using each model.Figure 2
Schematic diagram of segmentation results. (a) Input image. (b) Unet. (c) Mix_DeepLabv3+. (d) DeepLabv3+. (e) Rdrop_DeepLabv3+. (f) Super DeepLabv3+.
(a)(b)(c)(d)(e)(f)As can be seen from Figure2, for the denser buildings in the wilderness environment, the difficulty in extracting building information mainly lies in how to eliminate environmental influences and avoid misidentification of small-area objects. Compared with the existing algorithms, the proposed Super-DeepLabv3+ method can eliminate the interference of two small-area objects in the upper left corner and upper right part of the screen and identify the outline of the building more clearly and accurately. The following will quantitatively compare the accuracy of each network model from the perspective of data analysis, as shown in Table 3.Table 3
Accuracy comparison of each network model.
Network nameAccAcc_classmIoUFWloUUnet0.86300.90650.85390.9006Mix_DeepLabv3+0.98320.94060.89580.9681DeepLabv3+0.98300.93710.89390.9676Rdrop_DeepLabv3+0.98360.94290.89850.9689Super DeepLabv3+0.98340.95380.89930.9688The proposed Super-DeepLabv3+ method is only 0.02% lower than the Rdrop_DeepLabv3+ method in terms of Acc. Compared with Unet, Mix_DeepLabv3+, DeepLabv3 and Rdrop_DeepLabv3+ methods, Acc_class is improved by 4.73%, 1.32%, 1.67%, and 1.09% respectively. Overall, the Super-DeepLabv3+ method achieves the best segmentation accuracy.In terms of mIoU and FWloU, the proposed Super-DeepLabv3+ method is also at a higher level than other methods. This is due to the fact that the proposed Super-DeepLabv3+ method takes KL divergence minimization as the objective constraint training dataset based on regularization to optimize the segmentation results. So that the resolution of the predicted segmentation map can be restored, and it can be fused with the shallow feature map rich in localization information. While improving the performance of building information extraction, the division of building edges is also smoother, and a higher segmentation accuracy is achieved.Combining the four accuracy evaluation indicators, the Super-DeepLabv3+ method has the best remote sensing image segmentation performance, which significantly improves the accuracy and quality of building information extraction.


## 4.1. Network Parameter Settings

Adam optimizer is used during training. The primary parameter is the learning rate, which refers to back-propagating the output error to the network parameters to fit the output of the sample. In essence, the optimization process tends to the optimal solution step by step, but how much error each update parameter utilizes needs to be controlled by a parameter. This parameter is the learning rate Learning rate, and the initial learning rate is set to 0.001. At the same time, the optimal learning rate is not a fixed value, but a variable value that decays with the number of training sessions. That is, in the early stage of training, the learning rate is relatively large, and as the training progresses, the learning rate continues to decrease until the model converges. In the experiment, the median frequency balanced cross-entropy loss function is used to assist training, and the learning rate is attenuated by the Poly decay strategy, and the weight decay is 0.0005. That is, use formula (8) to adjust the learning rate.(8)prepoch=prepoch−11−epochmax_epoch0.9.In the formula,prepoch represents the learning rate of the current epoch, prepoch−1 represents the learning rate of the previous epoch, and max_epoch represents the set maximum epoch. An epoch means that all data is sent to the network, and a process of forward calculation + backpropagation is completed. As the number of epochs increases, so does the number of updates to the weights in the neural network. The curve goes from the initial unfit state to the optimal fitting state, and finally to overfitting. According to the actual verification, the maximum epoch of this experiment is set to 200, and the validation set is used for evaluation after each epoch. If the evaluation index does not improve for 10 consecutive epochs, the training is terminated.


## 4.2. Evaluation Indicators

The experimental evaluation indicators include algorithm efficiency and algorithm accuracy. The performance of the remote sensing image building information extraction algorithm can be relatively comprehensively summarized and described.


### 4.2.1. Algorithm Efficiency Related Evaluation Index

In terms of algorithm efficiency, the convergence time, inference occupied video memory and inference speed are selected as the evaluation criteria.(1)
The convergence time of the algorithm refers to whether the algorithm can finally find the global optimal solution of the problem, and the time required to find the optimal solution. Therefore, the meaning of fast convergence is that relatively accurate values can be obtained with fewer iterations.(2)
In inference tasks, there are three main parts that occupy GPU memory: model weights, input and output, and intermediate results. Deep learning models are often stacked with layers with similar structures, such as convolutional layers, pooling layers, fully connected layers, and activation function layers. Some layers have parameters. For example, the parameter of the convolutional layer is a high-dimensional convolution kernel, and the parameter of the fully connected layer is a two-dimensional matrix. There are also some layers without parameters, such as activation function layers, pooling layers, etc. Therefore, different model weights are formed. In the forward calculation, the output of the previous layer corresponds to the input of the next layer, and the intermediate results connecting the two adjacent layers also need GPU memory to save. Compared to the model weights and intermediate results, the GPU memory occupied by the input and output is relatively small. At the same time, due to the existence of backpropagation in the training phase, the usage of GPU memory will be more complicated.(3)
In deep learning, inference refers to a forward propagation process of a neural network. That is, the process of feeding input data into a neural network and then getting an output from it. The inference speed is the time from the image input model after preprocessing to the model output result. The inference speed of a model on a specific hardware is not only affected by the amount of computation, but also affected by many factors such as the inventory, hardware characteristics, software implementation, and system environment.


### 4.2.2. Algorithm Accuracy Related Evaluation Index

In terms of algorithm accuracy, with the ground truth map as a reference, the evaluation index can be used to quantitatively analyze the segmentation results. First, it is assumed that there aren+1 classification categories 0−n in the ground object segmentation dataset, and category 0 represents the background. Using pij to indicate that the true classification label of a certain pixel is i, and the label predicted by the network model is j. When i=j, the prediction is called true positive (TP) if i is a foreground sample, and true negative (TN) if i is a background sample. When i≠j, if i is a foreground sample, the prediction is called a false negative (FN), and if i is a background sample, the prediction is called a false positive (FP). Select the accuracy rate (Acc), class accuracy rate (Acc_class), mean intersection over union (mIoU), and frequency weight intersection over union (FWloU) several evaluation indicators to evaluate the accuracy of the model.Acc represents the proportion of correctly classified pixels in all pixels, and the calculation method is shown in the following equation:(9)Acc=TP+TNTP+TN+FN+FP.Acc_class indicates that for each class, the number of correct predictions for this class/the number of all predictions for this class. Calculate the proportion of correctly classified pixels to all predicted pixels of that class, and then accumulate and average, as shown in the following equation:(10)Accclass=1NTPTP+FP.IoU refers to the ratio of the intersection and union between the true set of each classification category and the correctly classified predicted set, as shown in the following equation:(11)IoU=TPTP+FP+FN=∑i=1Nnii∑i=1Nmi+∑j=1Nnji−nii.Here, mIoU refers to the average of the ratio of the intersection and union between the label value and the correct predicted value of each classification category, as shown in the following formula:(12)mIoU=1NTPTP+FP+FN=1N∑i=1Nnii∑i=1Nmi+∑j=1Nnji−nii.FWIoU is to set weights according to the frequency of occurrence of each class, and the weights are multiplied by the IoU of each class and summed. The formula is as follows:(13)FWIoU=TPTP+FP+FNTP+FNTP+FP+FN=1∑j=1N∑i=1Nnii∑i=1N∑j=1Nniinij∑i=1Nmi+∑j=1Nnji−nii.


## 4.2.1. Algorithm Efficiency Related Evaluation Index

In terms of algorithm efficiency, the convergence time, inference occupied video memory and inference speed are selected as the evaluation criteria.(1)
The convergence time of the algorithm refers to whether the algorithm can finally find the global optimal solution of the problem, and the time required to find the optimal solution. Therefore, the meaning of fast convergence is that relatively accurate values can be obtained with fewer iterations.(2)
In inference tasks, there are three main parts that occupy GPU memory: model weights, input and output, and intermediate results. Deep learning models are often stacked with layers with similar structures, such as convolutional layers, pooling layers, fully connected layers, and activation function layers. Some layers have parameters. For example, the parameter of the convolutional layer is a high-dimensional convolution kernel, and the parameter of the fully connected layer is a two-dimensional matrix. There are also some layers without parameters, such as activation function layers, pooling layers, etc. Therefore, different model weights are formed. In the forward calculation, the output of the previous layer corresponds to the input of the next layer, and the intermediate results connecting the two adjacent layers also need GPU memory to save. Compared to the model weights and intermediate results, the GPU memory occupied by the input and output is relatively small. At the same time, due to the existence of backpropagation in the training phase, the usage of GPU memory will be more complicated.(3)
In deep learning, inference refers to a forward propagation process of a neural network. That is, the process of feeding input data into a neural network and then getting an output from it. The inference speed is the time from the image input model after preprocessing to the model output result. The inference speed of a model on a specific hardware is not only affected by the amount of computation, but also affected by many factors such as the inventory, hardware characteristics, software implementation, and system environment.


## 4.2.2. Algorithm Accuracy Related Evaluation Index

In terms of algorithm accuracy, with the ground truth map as a reference, the evaluation index can be used to quantitatively analyze the segmentation results. First, it is assumed that there aren+1 classification categories 0−n in the ground object segmentation dataset, and category 0 represents the background. Using pij to indicate that the true classification label of a certain pixel is i, and the label predicted by the network model is j. When i=j, the prediction is called true positive (TP) if i is a foreground sample, and true negative (TN) if i is a background sample. When i≠j, if i is a foreground sample, the prediction is called a false negative (FN), and if i is a background sample, the prediction is called a false positive (FP). Select the accuracy rate (Acc), class accuracy rate (Acc_class), mean intersection over union (mIoU), and frequency weight intersection over union (FWloU) several evaluation indicators to evaluate the accuracy of the model.Acc represents the proportion of correctly classified pixels in all pixels, and the calculation method is shown in the following equation:(9)Acc=TP+TNTP+TN+FN+FP.Acc_class indicates that for each class, the number of correct predictions for this class/the number of all predictions for this class. Calculate the proportion of correctly classified pixels to all predicted pixels of that class, and then accumulate and average, as shown in the following equation:(10)Accclass=1NTPTP+FP.IoU refers to the ratio of the intersection and union between the true set of each classification category and the correctly classified predicted set, as shown in the following equation:(11)IoU=TPTP+FP+FN=∑i=1Nnii∑i=1Nmi+∑j=1Nnji−nii.Here, mIoU refers to the average of the ratio of the intersection and union between the label value and the correct predicted value of each classification category, as shown in the following formula:(12)mIoU=1NTPTP+FP+FN=1N∑i=1Nnii∑i=1Nmi+∑j=1Nnji−nii.FWIoU is to set weights according to the frequency of occurrence of each class, and the weights are multiplied by the IoU of each class and summed. The formula is as follows:(13)FWIoU=TPTP+FP+FNTP+FNTP+FP+FN=1∑j=1N∑i=1Nnii∑i=1N∑j=1Nniinij∑i=1Nmi+∑j=1Nnji−nii.


## 4.3. Remote Sensing Image Dataset

In order to verify the performance of the Super-DeepLabv3+ model for extracting building information from remote sensing images, a self-built dataset was selected to evaluate the model results. The dataset has a total of 127 images, covering a variety of scenes containing sparse and dense buildings. The number of images in each scene varies from 50 to 60. The horizontal and vertical resolution of each image is 96 dpi. To facilitate training, by randomly splitting between tiles. The dataset is divided into training set, validation set, and test set according to the ratio of 8 : 1 : 1. That is, 104 images are divided into training set, 11 images are divided into a validation set, and 12 images are divided into test set.Usually, the size of remote sensing images is large, and it is difficult to directly input into the model. The remote sensing image needs to be cropped into multiple small-sized subimages, then input into the model for prediction, and then stitched to obtain the final segmentation result. If no measures are taken, stitching marks may occur. The main reason is that the original remote sensing image has been cropped, and the feature information at the edge of the small-size subimage is incomplete, resulting in the loss of some of the above-given information in the small-size subimage. In order to eliminate the stitching traces, the remote sensing images need to be cropped into small-sized subimages by overlapping sliding windows. The prediction results of the small-sized subimages are obtained by the model and then stitched in sequence. It should be noted that the edge regions of the prediction results of small-sized subimages are ignored during stitching. In the experiment, the dataset is cropped into subimages of 256 pixels × 256 pixels according to the sliding window overlap step size of 40 pixels. At the same time, the images of the training set are expanded by scaling, flipping, color transforming, adding noise, and random erasing to improve the generalization ability of the model.


## 4.4. Experimental Results

In the experiment, five semantic segmentation networks were trained on remote sensing feature segmentation datasets, including Unet network model [26], Mix_DeepLabv3+ network model, DeepLabv3+ network model [7], Rdrop_DeepLabv3+ network model, and Super-DeepLabv3+ network model. And, a more comprehensive comparison and reason analysis are carried out on the algorithm execution efficiency and accuracy of the trained model. The segmentation performance of the network model is further intuitively evaluated by data analysis, and its shortcomings are analyzed.


### 4.4.1. Comparison of the Execution Efficiency of Different Remote Sensing Image Information Extraction Methods

In Table2 shows the comparison of video memory occupied, convergence time and inference speed for each network model training.Table 2
Efficiency comparison of various network models.
Network nameConvergence time (h)Inference occupies video memory (GB)Inference speed (fps)Unet63.320.5Mix_DeepLabv3+84.216.7DeepLabv3+104.317.6Rdrop_DeepLabv3+73.715.1Super DeepLabv3+73.614.8For the model convergence time, from the training results, the Unet network model has the fastest convergence speed, which takes 6 hours. The slowest is the DeepLabv3+ network model, which takes 10 hours to train from start to convergence. Although the five network models have long or short convergence times in a fixed training period, the overall difference is not large. This is because the batch normalization layer is used in the implementation of the network model, which can prevent the gradient from exploding. The mean and standard deviation calculated on the mini-batch are used to dynamically adjust the segmentation of the output of the intermediate layer of the deep convolutional neural network, so that the entire network is more stable in the intermediate output of each layer, thereby accelerating the convergence speed. The learning rate decay strategy used in training enables the network model to avoid the explosion of loss values during the training process, and then achieve convergence.For inference that occupies video memory, when the training batch size and input image size are fixed, a network model with a large number of parameters will occupy more video memory. It can be seen from Table2 that the Unet network model inference occupies 3.3 GB of video memory, and the inference occupies the least video memory. Because the Unet network model uses skip connections between each corresponding layer of the encoder network and the decoder network to perform feature fusion. Therefore, the intermediate feature maps of each stage in the encoder network need to be stored during training. Although this will lead to a larger video memory occupied by inference, the total occupancy is minimal because the number of intermediate feature map channels in Unet is designed to be less. DeepLabv3+ network model inference occupies the largest video memory, which is 4.3 GB. This is because the DeepLabv3+ network model also performs feature fusion with the shallow feature map of the encoder network in the process of restoring the resolution of the feature map, which requires additional storage of the intermediate feature map of the encoder during training.For inference speed, the Super-DeepLabv3+ network model has the fastest inference speed of 14.8 fps. This is because the Super-DeepLabv3+ network model is regularized during data training. On this basis, the Mixconv2d convolution is further used to replace the original deep convolution network, which reduces the number of parameters while ensuring the same accuracy. Compared with other methods, the proposed Super-DeepLabv3+ method significantly improves the efficiency and performance of the algorithm on the basis of ensuring convergence and ensures the effective execution of remote sensing image information extraction.


### 4.4.2. Comparison of Accuracy of Different Remote Sensing Image Information Extraction Methods

In terms of the accuracy comparison of different remote sensing image information extraction methods, a typical remote sensing building image is taken as an example to compare the performance between the models. Figures2(a)–2(f) are the original images of remote sensing buildings, and the extraction results of building information using each model.Figure 2
Schematic diagram of segmentation results. (a) Input image. (b) Unet. (c) Mix_DeepLabv3+. (d) DeepLabv3+. (e) Rdrop_DeepLabv3+. (f) Super DeepLabv3+.
(a)(b)(c)(d)(e)(f)As can be seen from Figure2, for the denser buildings in the wilderness environment, the difficulty in extracting building information mainly lies in how to eliminate environmental influences and avoid misidentification of small-area objects. Compared with the existing algorithms, the proposed Super-DeepLabv3+ method can eliminate the interference of two small-area objects in the upper left corner and upper right part of the screen and identify the outline of the building more clearly and accurately. The following will quantitatively compare the accuracy of each network model from the perspective of data analysis, as shown in Table 3.Table 3
Accuracy comparison of each network model.
Network nameAccAcc_classmIoUFWloUUnet0.86300.90650.85390.9006Mix_DeepLabv3+0.98320.94060.89580.9681DeepLabv3+0.98300.93710.89390.9676Rdrop_DeepLabv3+0.98360.94290.89850.9689Super DeepLabv3+0.98340.95380.89930.9688The proposed Super-DeepLabv3+ method is only 0.02% lower than the Rdrop_DeepLabv3+ method in terms of Acc. Compared with Unet, Mix_DeepLabv3+, DeepLabv3 and Rdrop_DeepLabv3+ methods, Acc_class is improved by 4.73%, 1.32%, 1.67%, and 1.09% respectively. Overall, the Super-DeepLabv3+ method achieves the best segmentation accuracy.In terms of mIoU and FWloU, the proposed Super-DeepLabv3+ method is also at a higher level than other methods. This is due to the fact that the proposed Super-DeepLabv3+ method takes KL divergence minimization as the objective constraint training dataset based on regularization to optimize the segmentation results. So that the resolution of the predicted segmentation map can be restored, and it can be fused with the shallow feature map rich in localization information. While improving the performance of building information extraction, the division of building edges is also smoother, and a higher segmentation accuracy is achieved.Combining the four accuracy evaluation indicators, the Super-DeepLabv3+ method has the best remote sensing image segmentation performance, which significantly improves the accuracy and quality of building information extraction.


## 4.4.1. Comparison of the Execution Efficiency of Different Remote Sensing Image Information Extraction Methods

In Table2 shows the comparison of video memory occupied, convergence time and inference speed for each network model training.Table 2
Efficiency comparison of various network models.
Network nameConvergence time (h)Inference occupies video memory (GB)Inference speed (fps)Unet63.320.5Mix_DeepLabv3+84.216.7DeepLabv3+104.317.6Rdrop_DeepLabv3+73.715.1Super DeepLabv3+73.614.8For the model convergence time, from the training results, the Unet network model has the fastest convergence speed, which takes 6 hours. The slowest is the DeepLabv3+ network model, which takes 10 hours to train from start to convergence. Although the five network models have long or short convergence times in a fixed training period, the overall difference is not large. This is because the batch normalization layer is used in the implementation of the network model, which can prevent the gradient from exploding. The mean and standard deviation calculated on the mini-batch are used to dynamically adjust the segmentation of the output of the intermediate layer of the deep convolutional neural network, so that the entire network is more stable in the intermediate output of each layer, thereby accelerating the convergence speed. The learning rate decay strategy used in training enables the network model to avoid the explosion of loss values during the training process, and then achieve convergence.For inference that occupies video memory, when the training batch size and input image size are fixed, a network model with a large number of parameters will occupy more video memory. It can be seen from Table2 that the Unet network model inference occupies 3.3 GB of video memory, and the inference occupies the least video memory. Because the Unet network model uses skip connections between each corresponding layer of the encoder network and the decoder network to perform feature fusion. Therefore, the intermediate feature maps of each stage in the encoder network need to be stored during training. Although this will lead to a larger video memory occupied by inference, the total occupancy is minimal because the number of intermediate feature map channels in Unet is designed to be less. DeepLabv3+ network model inference occupies the largest video memory, which is 4.3 GB. This is because the DeepLabv3+ network model also performs feature fusion with the shallow feature map of the encoder network in the process of restoring the resolution of the feature map, which requires additional storage of the intermediate feature map of the encoder during training.For inference speed, the Super-DeepLabv3+ network model has the fastest inference speed of 14.8 fps. This is because the Super-DeepLabv3+ network model is regularized during data training. On this basis, the Mixconv2d convolution is further used to replace the original deep convolution network, which reduces the number of parameters while ensuring the same accuracy. Compared with other methods, the proposed Super-DeepLabv3+ method significantly improves the efficiency and performance of the algorithm on the basis of ensuring convergence and ensures the effective execution of remote sensing image information extraction.


## 4.4.2. Comparison of Accuracy of Different Remote Sensing Image Information Extraction Methods

In terms of the accuracy comparison of different remote sensing image information extraction methods, a typical remote sensing building image is taken as an example to compare the performance between the models. Figures2(a)–2(f) are the original images of remote sensing buildings, and the extraction results of building information using each model.Figure 2
Schematic diagram of segmentation results. (a) Input image. (b) Unet. (c) Mix_DeepLabv3+. (d) DeepLabv3+. (e) Rdrop_DeepLabv3+. (f) Super DeepLabv3+.
(a)(b)(c)(d)(e)(f)As can be seen from Figure2, for the denser buildings in the wilderness environment, the difficulty in extracting building information mainly lies in how to eliminate environmental influences and avoid misidentification of small-area objects. Compared with the existing algorithms, the proposed Super-DeepLabv3+ method can eliminate the interference of two small-area objects in the upper left corner and upper right part of the screen and identify the outline of the building more clearly and accurately. The following will quantitatively compare the accuracy of each network model from the perspective of data analysis, as shown in Table 3.Table 3
Accuracy comparison of each network model.
Network nameAccAcc_classmIoUFWloUUnet0.86300.90650.85390.9006Mix_DeepLabv3+0.98320.94060.89580.9681DeepLabv3+0.98300.93710.89390.9676Rdrop_DeepLabv3+0.98360.94290.89850.9689Super DeepLabv3+0.98340.95380.89930.9688The proposed Super-DeepLabv3+ method is only 0.02% lower than the Rdrop_DeepLabv3+ method in terms of Acc. Compared with Unet, Mix_DeepLabv3+, DeepLabv3 and Rdrop_DeepLabv3+ methods, Acc_class is improved by 4.73%, 1.32%, 1.67%, and 1.09% respectively. Overall, the Super-DeepLabv3+ method achieves the best segmentation accuracy.In terms of mIoU and FWloU, the proposed Super-DeepLabv3+ method is also at a higher level than other methods. This is due to the fact that the proposed Super-DeepLabv3+ method takes KL divergence minimization as the objective constraint training dataset based on regularization to optimize the segmentation results. So that the resolution of the predicted segmentation map can be restored, and it can be fused with the shallow feature map rich in localization information. While improving the performance of building information extraction, the division of building edges is also smoother, and a higher segmentation accuracy is achieved.Combining the four accuracy evaluation indicators, the Super-DeepLabv3+ method has the best remote sensing image segmentation performance, which significantly improves the accuracy and quality of building information extraction.


## 5. Conclusion

Aiming at the characteristics of a large amount of remote sensing image data and various types, a remote sensing image feature recognition method combining DeepLabv3+ and Mixconv2d is proposed. (1) The deep learning semantic segmentation model DeepLabv3+ and Mixconv2d are combined, and convolution kernels of different sizes are used for feature recognition. (2) The regularization method based on Rdrop Loss improves the accuracy and efficiency of contour capture for objects of different resolutions, and at the same time improves the consistency of dataset fitting. (3) Experiments based on self-built datasets show that Super-DeepLabv3+ has good accuracy and execution efficiency, which fully proves the effectiveness of the method. In the next step, we will deeply study how to further extend the applicability of the algorithm on the basis of ensuring the efficiency and calculation accuracy of the algorithm.



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*Source: 9968665-2022-10-12.xml*