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开始:Tutorial: Reading and Transforming Satellite Imagery in FME| Next:使用卫星图像的光栅阅读器
In this article,we will have a look at a few different rasters while pointing out some of the important aspects in each.我们将研究光栅图像之间的相似性和差异。可以使用4种不同的标准对光栅进行分类:
1) georeferenced status
2) interpretation (band number/type/bitness)
3)扫描/拍照/光栅化
4) contents - imagery/dem/topographic/thematic
For another approach to viewing rasters,看看这篇文章Viewing and Inspecting Rasters.请从下载和提取下面的rasterpackage.zip开始。
在FME数据检查员中,open 1_smartphonephoto.jpg using the JPEG (Joint Photographic Experts Group) format.为了检查它,启用“选择功能和显示信息”,然后单击不同的单个像素以发现有关它们的信息。
'Select features and display information' enabled.
You can also drag a rectangle on the image in View window and release to get information about the whole raster.
Draw a rectangle over the raster to obtain information about the whole raster.
Take note of the following:
1_smartphonephoto.jpg as seen in the FME Data Inspector:In the bottom left we see the pixel information including the Ground Location,以及单个波段值。这是一个像素,从中间的叶子开始,note the high Band 0 Red value compared with the other bands.On the right,我们看到了一些元数据,这些元数据来自于FME收集到的图像。想知道乐队名称中的数字是什么(例如,红色8)?这个数字代表位的深度。更高的位深度允许在一个频带中存储更多信息或更大范围的值。For 8 bit bands,we can only store values up to 255.The higher bit depth,however,usually means the file will typically become bigger in size.
使用tiff(标记图像文件格式)或geotiff(地理参考标记图像文件格式)打开aerial geotiff(2_aerial.tif)并进行检查。请注意与上一个光栅的不同之处:
2_Aerial.tif:Similar to what we saw in the above example,however,现在我们的图像有一个定义的坐标系,并且图像是地理参考的。If you have background maps enables you should see that it sits nicely over Vancouver's waterfront.
Inspect the scanned image (3_scannedTopomap.tif),检查此图像与前两个图像的区别:
A section of3_scannedTopomap.tif:这里我们可以看到右边的调色板信息,note that for each value in the UNIT8 band we can see a corresponding RGB color.
Open and inspect the digital elevation model,CDED光栅,(4_elevations_cded.dem)使用加拿大数字高程数据(cded)格式。
A section of 4_elevations_cded.dem as seen the FME Data Inspector:这里我们可以看到Int32波段,它的值与海拔相对应。我能找到的最高点是1497米。
Open and inspect the Landsat image (LC80480252014249LGN00.tif) using TIFF (Tagged Image File Format) or GeoTIFF (Geo-referenced Tagged Image File Format).这个可能需要更长的时间来加载,因为它非常大。
在FME数据检查员中看到的陆地卫星图像:在这里我们可以看到它有四个波段,其中一个叫做alpha16。An invisible pixel has been selected for the screenshot.请注意,alpha16波段的值为“0”,这相当于一个完全透明的像素。If we didn't have the alpha band here the border would look black (0,0,0).The reason this file is so large is because we have four 16 bit bands with a fairly high resolution.
Raster Bit Masks: Making Sense of the Numbers
Making RGB Images with Sentinel Data
Tutorial: Reading and Transforming Satellite Imagery in FME
Raster to Raster Translation (Geotiff to JPEG) with Reprojection
Raster Calculations and Raster Palettes
Using Conditions with the RasterExpressionEvaluator Transformer
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