Category Archives: Raster
LAS Dataset: How to use the 3D Analyst toolbar with my LAS Dataset
Lidar data is become increasingly available and there are likewise new tools to analyze and display the data. LAS is the public file format for the interchange of three dimensional point cloud data between data users. LAS information can be … Continue reading
3D Analyst Toolset Recommended Workflow: Consider the geometry of the features being used
With the release of ArcGIS 10, new tools were made available, allowing you to use 3D objects in geoprocessing tools, and opening up new possibilities for proximity analysis. One of the new tools is the Near 3D tool, which calculates the three-dimensional distance from each input feature to the nearest feature residing in or more nearby feature classes. However, when using the new 3D analysis tools, it’s always important to consider the geometry of the features being used. Continue reading
5 Minute Trouble Shooting – Changing the Units on a Profile Graph
“Why does my profile graph show an elevation change of 11 feet over 1,111,111 feet?”
In general, profiles show the change in elevation of a surface along a line. They help to assess the difficulty of a trail for hiking or biking, or to evaluate the feasibility of placing a rail line along a given route.
A Profile Graph represents height on the Y axis and horizontal distance on the X axis. The unit of distance along the X axis depends upon the units of the projected coordinate system (PCS) of the elevation raster data. For example, if data is in a Universal Transverse Mercator (UTM) PCS, the unit of distance will be in meters; if data is in State Plane PCS, the unit of distance will be in feet (US) as shown in the following figure.
Table or Dataset? That is the question… if you are talking about a Mosaic Dataset
The Add Raster to Mosaic Dataset tool has many input options to consider when adding your data, including choice of raster type. Within the help documentation, there are twenty one different raster types to choose from among sensor products, aerial imagery, … Continue reading
Esri GRIDs are always 32 bit
There are many different kinds of rasters that can be used in ArcMap. To better describe and explain these different kinds of rasters, Esri has created help documentation on technical specifications and supported raster formats. Included in the documentation is … Continue reading
What is Esri CityEngine?
I am sure many of you have already heard about CityEngine, and some of you may have even already contacted Support Services with questions related to it. For those who haven’t been introduced, CityEngine is a stand-alone software product that provides professional users in … Continue reading
Calculating the slope of a hiking trail
Trail hiking can be a fun and exciting activity when you properly prepare for the hike. An important step for preparation is knowing the trail. Some key factors include: length, minimum elevation, maximum elevation, and slope. If you do not … Continue reading
Get Your Free Raster Data Here!
As a raster analyst, there are a lot times I try to “fix” many types of raster data from various online sources. If you’re going to get data from elsewhere, there are many reliable sources available for GIS data, some websites that charge a fee, and some that are really well-done free clearing houses and data centers.
Null Doesn’t Mean Zero?
How to add different-sized rasters with NoData Values
One of the most common forum topics is on how to add two rasters with different spatial extents and get a result more than just where the two rasters overlap. Well, the reason the result is only those areas has to do with null values.
There are environment variables to modify to ensure that the rasters line up (snap raster) and the extent is preserved during the process (Spatial Extent). Fixing the environment setting alone will still not fix the output of the process. If you modify the spatial extent to match the “union of inputs”, the output raster will have the correct spatial extent, but the only values will be the values where the two rasters overlapped. So what is going wrong?
Obviously it is the pixel values … or, wait, I guess it isn’t that obvious. Try this piece of wisdom provided by forum poster and Product Engineer, Eric R.
Pixel value + NoData Pixel = NoData Pixel
Pixel value + 0 = Pixel value
Pixel value + Nothing (because your extents are different) = Nothing.
Two different rasters used in calculation (NoData is red).
Sum of Rasters
You may be asking, “What is actually happening? Are the values being used in the analysis or not?” Well, the answer is they will be as long as part of that equation doesn’t include a null value. If there is a null value present that will make the output null, then the output will not be correct.
The next question is how to fix it. Bear in mind, both solutions require you to make the rasters that are being used as the inputs match in spatial extent, pixel registration and cell size. You can use the Copy Raster tool and set the appropriate environment settings to accomplish this. Once you have corrected the rasters, then there are two options depending on the desired output,
1. Set the NoData values to a value of zero, so that when they’re added together, the output will have the correct spatial extent and values from both rasters.
Output from Setting the NoData value (blue pixels = 0)
2. Utilize the Con( IsNull ) workflow to include all of the pixels and add them where appropriate.
Con(IsNull(“RasterSMALL”),”RasterBIG, (“RasterSMALL” + “RasterBIG”))
Output from Con Tool
To recap, there are options to handle the NoData cells. Depending on what output you’re trying achieve, there are different techniques. It’s also important to understand the effect that NoData has when used in raster calculation.
There is a related forum post that discusses using Python to sum multiple rasters together: Calculate sum of 2334 raster layers.
Jeff S. - Geodata Raster Support Analyst
Can I avoid using the internal overviews when I add rasters to my Mosaic Dataset?
Many of the menus and processes, such as the new geoprocessing toolset for example, have changed in ArcGIS 10.0. One of the biggest changes in ArcGIS 10.0 is the switch from Image Server to Mosaic Datasets.
Previously, in Image Server, you could use the Advanced menu to manually control the options when adding rasters to an image service.
However, there are several situations where rasters added to an ISDEF should not apply the internal overviews that are present with some raster formats. SIDs, and other rasters with multiple levels of pyramids, can affect the performance of image services. Since image services use overviews to increase performance, increasing the number of overviews will improve the performance.
When SIDs are added to an image service with the Advanced process under the General Tab, there is an option to “Include internal overviews”. If this option is unchecked the raster will be added without bringing in the pyramids that are in the raster. For highly compressed rasters like SIDs, there can be many levels of overviews built into the raster which affects the number of overviews created by the mosaic dataset or ISDEF.
In order to replicate the same workflow in ArcGIS 10.0, the Add Rasters To Mosaic Dataset tool includes a section of Raster Pyramid Options. In order to prevent the internal pyramids from being added to the mosaic dataset, set the value to zero (0). This increases the number of overviews that will need to be created, but the performance should be improved. If this option is not used, the overviews that are inherent with the SID will be used in place of overviews. So, the choice from a design perspective is whether to utilize the overviews of the rasters added to the mosaic dataset or to create new overviews for the mosaic dataset. This pyramid option is available for all raster formats, not just SIDs.
Add Rasters to Mosaic Dataset dialogue with Raster Pyramid Options
To recap, the ability to apply or ignore the internal pyramids and pyramids of input rasters is available in the Raster Pyramid Options section of the Add Raster to Mosaic Dataset tool.
Jeff S. - Geodata Raster Support Analyst
