Grainy TIF at Low Zoom Levels When Exporting Aerial Imagery from SID

AndrewSchwartz · ‎06-15-2018

I am building a Web App for a municipal government. The county recently commissioned some high res aerial imagery and the municipality wants this included as a custom basemap. They've given the imagery to me as a series of SID files. To make a tile package, first I need to mosaic the SIDs, clip them to be just around the municipality's borders, and then export as a single TIF.

When I did this, the resulting TIF comes out weirdly grainy when I am zoomed out, even though it it still high resolution at greater zoom levels. It's not an issue with stretch type, resampling, etc because I have the same settings applied to both layers.

SID:

TIF:

PeterBecker · ‎06-15-2018

What you are seeing is the combination of two things

1 - The default for creating pyramids of the TIF files was Nearest sampling which is causing the grainy appearance at small scales. This should be set to Bilinear/Average.

2 - An additional artifact of 1 is that the standard deviation of the histogram also increases. It is likely you are using a stdDev or percent clip and this causes the colors to be slightly different.

The method you are doing to create such a basemap can be much simpler and faster, without creating artifacts. There is No need to physically mosaic or clip the imagery.

Create a mosaic dataset. Add the MrSID files. Edit the Footprints or Boundary to clip out areas you do not want. Then use the mosaic dataset as input to the tilecaching tools.

For more detail on creating mosaic datasets etc see ArcGIS Imagery Workflows | ArcGIS . Check out the workflow managing Preprocessed Orthophotos. Also check out http://www.arcgis.com/home/item.html?id=b66bdaa9cec247c087cc836ada6fe2b1 which provides some tools to simplify the caching.

AndrewSchwartz · ‎06-18-2018

Hi Peter,

Thanks for taking the time to give me advice. You're right - the pixelation was caused by the nearest neighbor sampling. When I switched to bilinear, the image looks much better,

Regarding my workflow - the method you described is what I originally intended to do. However, when I tried to open the Create Mosiac Dataset tool (in box ArcMap and in Pro) I received a messaged saying that I don't have a license to execute the tool. I thought it was strange considering I have an organizational license, with spatial analyst extension enabled, but was in a rush so I just found a workaround.

PeterBecker · ‎06-18-2018

Creating and editing a mosaic dataset requires Standards level of ArcGIS Desktop. The tools are extensive and handle not only simple ortho's but a very wide range of image modalities. A mosaic dataset essentially references the data sources and defines the processing to be applied. A very wide range of processing can be applied including things like color correction and seamline generation. If any data is to be excluded then you can just edit the individual image footprints or the mosaic datasets boundary using standard editing tools (or import existing geometries) and the data will be clipped.

forestknutsen1 · ‎06-15-2018

Why do you need to make a single tiff. Can you not use a Mosaic Dataset (What is a mosaic dataset?—Help | ArcGIS for Desktop) Then you can set your AOI up in that with vector polygons. No, need for the time consuming classic mosaic and clip operations. Then you can burn your cache right from the MD. If the MD does not support your sid format (I have never used sid in an MD mayself). You can export your sid to tiff with lizardtech tools.

Geospatial image compression, manipulation, storage, and distribution for GIS workflows | LizardTech

Knowledge Base | Decoding a MrSID file to other formats | LizardTech

Hope that helps.

AndrewSchwartz · ‎06-18-2018

Hi Forest,

As I mentioned to Peter - when I tried to open the Create Mosiac Dataset tool (in box ArcMap and in Pro) I received a messaged saying that I don't have a license to execute the tool. I thought it was strange considering I have an organizational license, with spatial analyst extension enabled, but was in a rush so I just found a workaround.

Regarding your suggested workflow. I understand everything you're saying except for the part about "set your AOI up in that with vector polygons". Can you explain what you meant by this?

forestknutsen1 · ‎06-18-2018

Hi Susan,

License level: Sorry, I don't think I can be much help on this one. We are still in the "stone age" as far as gis software versions go. I have done much of my image processing on arc 10.3 with an advanced license. I bet Peter has some input on this one.

AOI: Area of interest. I was talking about the same thing as Peter:

Edit the Footprints or Boundary to clip out areas you do not want.

How To: Export footprints and boundary from a mosaic dataset

Import Mosaic Dataset Geometry—Help | ArcGIS Desktop

What I have done in the past is export the geometry edit them to what I want to show in the cache. Then import them back into the mosaic. This replaces the classic clip operation with out modifying the source raster data.

Using the MD can save you gobs of processing time if you have large amounts of data. But is less critical for small jobs. I love MD when working with stuff on my bigger jobs - where the raw tifs are in the 0.5 TB range.

Thanks,

Forest