Photographic ascending posture

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As a brand-new 3D GIS software, in the function of loading data, LocaSpaceViewer can widely support loading multiple data formats, which greatly enriches users' browsing requirements for data in different data sources. When loading different data sources, the loading speed often becomes an important key point in testing most GIS software. At present, tif format file is undoubtedly the most common image storage format in the storage of most satellite image data and orthographic images generated by oblique photography. So how does LocaSpaceViewer solve the problem of slow loading of tif format data? Come and have a look with me.

I. analysis of tif data format

Tif format is a marked image file format (TIFF), which is mainly used to store photos and artistic drawings.

TIFF, JPEG and PNG have become a popular high-bit color image format, which is widely used in the storage and conversion of images with high image quality requirements. Because of its flexible and inclusive structure, it has become the standard of image file format, and has been widely supported in the industry, such as image processing applications such as Photoshop of Adobe and GIMP of GIMP team, desktop printing and page typesetting applications such as QuarkXPress and Adobe InDesign, and scanning, fax, word processing, optical character recognition and other applications all support this format.

Once the volume is above 1GB, the general drawing software can't view it normally. Even professional GIS software such as ArcGis, GlobalMapper and LocaSpaceViewer. It will take a long time to load and display. And there is the problem of dragging, because the data need to be analyzed constantly.

Second, methods to improve the resolution speed of tif

Method 1: Create Pyramid

Pyramid is a method of storing raster images in copy mode, and the resolution gradually decreases. By choosing a resolution similar to the display area, only some queries and calculations are needed, thus reducing the display time. The basic principle of creating pyramids is to generate pyramids from bottom to top by sampling, and directly take one of them as the operation object according to the demand, thus improving the overall efficiency. The more levels built, the more convenient the query, but the greater the data redundancy.

Each successive layer of the pyramid is down-sampled at a ratio of 2: 1. Through the pyramid, the loading and parsing speed can be increased by 5- 10 times, but at the same time, the data volume will be increased by 1-2 times. This value is closely related to the compression algorithm of tif and whether it is compressed or not. There are several ways to create pyramids, such as ovr of Arcgis and rrd of Erdas. See appendix 1 for the specific steps of creating pyramids with Arcgis.

Advantages: data browsing speed is 5- 10 times faster.

Disadvantages: the amount of data increases, the number of files increases, and the ability to improve loading speed is limited.

Method 2: Cut data and publish wmts slicing service.

Using graphic cutting tools, large tif data can be divided into the following structures (the level is related to the resolution of the original data):

The block file consists of a series of hierarchical folders, and the folder structure is top-level directory/layer directory/column directory/block file. The "world" in the upper left corner of the diagram is the top-level directory, and its subfolders 0, 1, 2, 3 and 4 store tiles, 2, 3 and 4 corresponding to Level0, 1 and Level4 respectively. There are 16(0~ 15) folders under the layer directory 3, and each folder stores the tiles corresponding to the column, which is the column directory; The block pictures displayed on the right are all block pictures in the ninth column of the third-level directory. The file name of the picture is the line number where the block is located, and the picture format is png.

As can be seen from the above description, each block has a corresponding geographical scope and a corresponding index number (layer, column and row). When browsing global data in a 3D scene, you can determine which layer of tile needs to be called according to the level of the viewpoint and the range of the visual field.

Advantages: the browsing speed can be increased by more than 50 times.

Disadvantages: After being divided into tile data, the number of files increases sharply, resulting in file fragments and greatly reducing copy movement. The volume is increased by about 0.5 times.

Method 3: Convert tif format to lrp format with LocaSpaceViewer.

LocaSpaceViewer created the lrp format. Its principle is to divide data according to tile structure, compress a single tile with compression algorithm, and then store all tile files in lrp file in the form of binary stream. Lrp has its own index file, through which specific tile data can be queried, which is 10 times faster than ordinary tile structure. At the same time, it is guaranteed that there is still only one file, but the browsing speed can be increased by more than 100 times. Because of tile compression, the data volume will even shrink, and the normal file volume will increase by -0.5 to 0.5 times. Moreover, lrp format also supports the loading and browsing of mobile devices and the caching of offline data packets, which is very convenient for users. See Appendix II for the specific steps of converting tif format into lrp format in LocaSpaceViewer.

Advantages: Not only can the pyramid structure be established for spatial indexing, but also high compression and ultra-fast loading speed can be realized.

Disadvantages: Not found so far.

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As a powerful 3D digital earth software, LocaSpaceViewer can support loading almost all GIS data formats, including tif and lrp formats. Users can use LocaSpaceViewer to load their own tif files, or they can convert tif files into lrp format in LocaSpaceViewer before loading.

Users who have used LocaSpaceViewer can clearly feel that loading lrp files with LocaSpaceViewer can effectively solve the problem of slow loading of tif files with large data, and its advantages are self-evident. A single lrp can hold data of 1tb, and the compression ratio is 1: 10, which means that 10 LRP can store tif data of 10tb. After a single tif file reaches more than 2GB, it will be slow to view it in common software tools. However, after converting to lrp format in LocaSpaceViewer, the loading speed can almost reach the level of seconds plus, and its speed can be imagined. So, with me, use LocaSpaceViewer to convert into lrp files, solve the problem of slow loading of tif data, and make your picture loading speed no longer a problem!

Appendix I: Process of Creating Pyramids in Arcgis

A: Click Open Toolbox to create a building pyramid.

B: select the pyramid level (optional)

Pyramid levels refer to the number of pyramid levels established. The default level is-1, and a complete image pyramid will be built. The highest level of the pyramid can be set to 29, which can be set according to the actual situation. The more levels, the longer it takes.

C: Select resampling method pyramid resampling technology (optional).

There are generally three resampling methods: bilinear interpolation method, nearest pixel method and cubic convolution method. The nearest pixel method is the fastest and the cubic convolution is the slowest, but the resampling image is the best.

D: Select compression method. Pyramid compression type (optional).

You can choose the compression method or not to compress the pyramid.

Appendix 2: the process of converting tif into lrp with LocaSpaceViewer

Answer: Open LocaSpaceViewer, and in the Data Processing menu, click Image Batch Processing or Terrain Batch Processing (take image data as an example here).

A dialog box pops up, and click Add Data or Add Directory to add a single image data or multiple image data of the whole folder. Here, we select a single add data to add the image data in tif format to be converted. LocaSpaceViewer can convert multiple files at a time. If converting a single data, you can directly add a single data for conversion.

You can click Delete Data or Delete All, and you can select new data or all data in the dialog box to delete.

B: Start converting images.

After adding the data to be converted in turn, you can convert the image. Three tif files have been added here to convert to lrp format.

Browse results

After data conversion, a dialog box will pop up whether to preview the processing results. Click Yes to preview the conversion results. Adding and converting three tif files here is very fast. In just a few seconds, you can see multiple data results converted to lrp format in the layer of the sidebar, which is very fast for zooming or expanding browsing.

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