امروزه تصاویر هوایی با در اختیار گذاشتن منابع مختلف داده یکی از کارآمدترین راههای کسب و استخراج اطلاعات مکانی دقیق و بههنگام است. که در پروسه تهیه اطلاعات مکانی از این منابع، مشکلترین بخش استخراج عوارض موجود در تصاویر میباشد. در این تحقیق یک روش متفاوت جهت استخراج ساختمانها با استفاده از دادههای لیدار هوابرد و تصاویر اولتراکم بر روی محدوده مشخصی از شهر بندر انزلی با انواع تراکم ساختمانی پیادهسازی شد. سیستم پیشنهادی از اطلاعات هندسی و مکانی دادههای لیدار و تصاویر اولتراکم استفاده کرده که شامل سه مرحله کلی میباشد، در مرحله اول، دادههای لیدار فیلتر شدند و با استفاده از خوشهبندی طیفی در محیط eCoginition، ساختمانها استخراج شد. در مرحله دوم، مدل به دست آمده با مرزهای دو بعدی ساختمانها که به روش حد آستانه ارتفاعی در محیط ENVI Lidar به دست آمده بود مقایسه گردید. در مرحله سوم؛ پس از استخراج، مرزهای اولیه ساختمانی با ساختمانهای استخراج شده از طریق الگوریتم شطرنجی، ادغام شدند. در بخش خطایابی ساختمانها به ساختمانهای دارای خطا پرداخته شد. ارزیابی نتایج نشان داد که سیستم به کار گرفته شده به طور نسبی به اهداف تعیین شده رسیده است. خطای تک تک ساختمانها ابتدا به صورت کلی و سپس به صورت جزئی مورد بررسی قرار گرفت و مشخص گردید تکنولوژی لیدار هوایی قابلیت فوق العادهای را در جمعآوری نمونههای بسیار دقیق و متراکم از اندازهگیریهای ارتفاعی سطح شهرها دارد و میتوان سطح جدیدی از جزئیات اطلاعات دقیق تراکم ساختمان را به طور اتوماتیک و کارآمد از دادههای لیدار هوایی استخراج کرد. در تعداد 417 ساختمانی که مورد بررسی و تجزیه و تحلیل قرار گرفت دستیابی به ارتفاع ساختمانها با دقت بسیار بالا میسر گردید و تمامی ساختمانهای محدوده مورد مطالعه با تراکم فشرده و ارگانیک و نیز پراکنده و برنامهریزی شده استخراج گردیدند.
عنوان مقاله [English]
Evaluating and measuring the extracted data of buildings with using lidar
Extraction and processing of various features with the help of aerial imagery reduces the time and financial costs associated with the use of ground mapping and the resulting human error. Advances in the field of aerial sensors in terms of spatial and spectral resolution with precise place and performance picking up altitude from the ground have led to the use of each part of information about terrestrial phenomena such as spectral and spatial characteristics Brought. Today, complementary data used to detect complications are Lidar data, the sensor of which is sent and received, and the electromagnetic spectrum in the near-infrared spectrum (in its aerial form) and joined the spectrum. Pays close infrared and green band (in space type).
DATA AND METHODS
Lidar data and spectral images were analyzed using different types of algorithms effective in landfill extraction to assess density. New layers of images were obtained in the form of raster from the study area, which was analyzed by performing slope extraction steps on flat and sloping surfaces. Buildings that were definitely not buildings were removed. The size and spectral characteristics of the missing structures were identified and the parcels were redistributed to extract the impermeable surfaces. Which led to the achievement of two levels of parcels and impenetrable points. The data set is related to the northern part of Bandar Anzali, which includes a vertical aerial photograph, irregular cloud points of the region with dense one to two points per square meter with an average point space of 0.69 square meters, and vertical aerial photograph with spatial resolution. It is 8 cm square.
RESULTS AND DISCUSSION
In this study, a different method for extracting buildings using airborne Lidar data and ultracam images was presented. The proposed system used geometric and spatial information of Lidar data and ultracam images, which included three general steps, in the first step; Lidar data were filtered and extracted using spectral clustering of buildings. In the second step; The obtained model was compared with the two-dimensional boundaries of buildings by the height threshold method. In the third step; After extraction, the first building boundaries were merged with the structures extracted by the checker algorithm. In the stage of separating terrestrial from non-terrestrial points, all points related to land were classified and extracted. The remaining points were classified as roof points, which were dealt with in the fault section of the buildings. All the functions used enabled the system to successfully extract the structures from the Lidar data.
The data for the first return points were subtracted from the data for the last return points and a fixed value was obtained which depended on the altitude accuracy of the difference between the two returns. In addition to the mentioned method, the clustering method was used during the research that each cluster belonged to a roof section so that the characteristics of each surface model could be easily determined.
Then, to complete the shape of the roof, the footprint of the building that was extracted was used. In fact, the borderlines and inner vertices extracted only part of the shape of the border. Other sections, such as vertical edges, were not detected due to intersection. This is due to the lack of front sampling. Finally, the items extracted through spectral clustering in eCoginition software and two-dimensional boundaries extracted from ENVI Lidar software, to increase the accuracy of land surface extraction (buildings) and make the area of buildings studied in this data Were merged. As mentioned; After extraction, the primary building boundaries were merged with the structures extracted by the checker algorithm. In the section of buildings diagnostics, buildings with errors were discussed and the evaluation of the results showed that the system used has relatively reached the set goals and the methods used include the threshold method. Elevation, clustering, spectral method, and integration method were evaluated for each of the four blocks with error rates of 28%, 15%, and 0%, respectively, based on the area of extracted tolls to the study area. The error of each building was first examined in general and then in detail, and it was found that aerial Lidar technology has an extraordinary ability to collect very right and dense samples of altitude measurements of cities and a new level of detail information can be Accurately extracted building density automatically and efficiently from aerial Lidar data. In 417 buildings that were surveyed and analyzed, the height of the buildings was achieved with high accuracy and all the buildings in the study area were extracted with a compact and organic density as well as scattered and planned.