Tag Archives: raster
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.
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
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
Georeferencing in ArcGIS 10 or “Why is my georeferencing toolbar suddenly grayed out?”
Questions on georeferencing are some of the most common questions that we get in Support. These conversations range from basic how to questions all the way to questions like “Why are the buttons grayed out?”
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
ArcGIS 9.3.1 SP2 QIP Windows 2008 MrSID Patch Released
The ArcGIS 9.3.1 SP2 QIP (Desktop, Engine, Server) Windows 2008 MrSID Patch is now live at the Resource Center. The patch addresses these two issues:
- When using MrSID raster data in the Windows 2008 operating system can cause the application to crash.
- Removing JPEG 2000 raster format data from the ArcMap table of contents in Windows 7 can cause the application to crash.
For more details and to download the patch, please visit:
http://resources.arcgis.com/content/patches-and-service-packs?fa=viewPatch&PID=17&MetaID=1790
Do Your Rasters Know What Time It Is?
Viewing a series of rasters according to a timeline usually ends with turning on/off the layers to produce the desired visual affect. This process, along with many other techniques for looking at data over time, has been fairly challenging.
In ArcGIS 10, the ability to time-enable spatial data has opened a whole new dimension to the visualization of information.
Imagery, temperature and precipitation are just a few examples that can be placed into a mosaic dataset or raster catalog to represent a change over time. The following example enables time on a mosaic dataset. However, similar steps can be followed to activate time on a raster catalog.
Preparing your data:
1. Create a new mosaic dataset and add in the rasters.
(For detailed steps see: The workflow and tools to create mosaic datasets)
2. Open the attribute table of the mosaic dataset footprint.
3. Add a new ‘date’ type field.
4. Populate the field with the corresponding time values.
Enabling time on your data:
1. Right-click on the mosaic dataset in ArcMap > Properties > Time tab.
2. Select the Time Field.
3. Click Calculate to populate the time step interval and the layer time extent.
4. Adjust the time step interval to the desired value.
5. Click OK.
6. Open the Time Slider window from the Tools toolbar.
7. Enable time on map from the Time Slider window.
8. Use the time slider to step through each raster in the mosaic dataset.
Now with time enabled functionality, your rasters can know what time it is and provide you with an excellent option for visualizing data changes over time.
-Timothy H., Support Analyst – Geodata Raster Group, Esri Support Services – Charlotte, NC
Related Links:
How time is supported in spatial data
Having problems georeferencing your raster image?
Have you ever added a raster image to your map document only to find that some of the georeferencing tools are not available? You know you’ve done this many times in the past, but what’s different this time?
A quick test to identify any issues is to add the image to a new blank map document instead of an existing map document. If the tools are available in the new map document, then one of the reasons for the problem may be that your data frame in the existing map document is rotated. ArcMap can’t apply a double-transformation to the raster.
Here are the only functions available when the data frame is rotated:
- Update Georeferencing*
- Rectify*
- Reset Transformation*
- Flip or Rotate functions
- Rotate
- Shift
- Scale
*Available once image has been modified.
Simply clearing the data frame rotation will activate the following functions:
- Fit to Display
- Auto Adjust
- Add Control Points
- View Link Table
For more information on why your georeferencing toolbar may be grayed out, please reference the related links below.
-Timothy H., Support Analyst – Geodata Raster Group, Esri Support Services – Charlotte, NC
Related Links:
Problem: The georeferencing toolbar is greyed out
The GIS Encyclopedia: Georeference
Working with Rasters: Georeferencing
Is your raster so bright you have to wear shades?
Have you ever added a raster to an MXD and noticed that it looked different? Or created a mosaic dataset or raster catalog and suddenly, the rasters are so bright, you think, “What did ArcMap do to my raster?!”
