ESRI TIN to Elevation Raster Conversion


Hello and welcome to this video
tutorial. Today, I’m going to demonstrate how to
convert a TIN elevation dataset to an elevation raster using ArcGIS and the 3D analyst extension. Some background information before
we get started Different GIS packages and CAD packages often have their own formats for
TIN data and this can be troublesome because if
you want to use an elevation dataset between multiple packages you often have to convert it from one
format to another. TIN data in ESRI is stored as either a coverage file or a terrain dataset. Both of these files are proprietary ESRI
formats so there is limited support for them
in other mapping packages. Raster elevation datasets
on the other hand are widely supported in different GIS
packages. There are a number very common
formats including TIFF images, ERDAS Imagine files and ESRI binary grids. And these datasets they are very simple for these packages to
draw they don’t take a lot of time, they are fairly
portable and there are often not any limitations
on how these files can be used. They can often be used in the same way as that a TIN file would be used. So, in this tutorial I’m going to show you
how to convert a coverage TIN, so a TIN that is stored within an ESRI coverage file. l am going
to show you how to convert from this to an ERDAS Imagine image. Now, this process will work for other raster formats such as TIFFS, Grids, BIL Images, etc. One thing that is important to note is
that we don’t want to use a raster format that uses compression, such as JPGs, ECW files, etc. The reason is that for a raster elevation
dataset to be it’s going to use the precise elevation values are stored in image and using a compressed image
format destroys these elevation values. It can still be used as a
background image but you can’t interrogate those specific pixel values or perform other GIS operations. So, be sure to use an uncompressed format. So, first what we want to do is setup our catalog so that we have the necessary tools
available. So first up, we are going to disable
background Geoprocessing. Now, the reason we doing this is that background geoprocessing works just fine but it gives you less
diagnostic information. When you’re running a tool, you’ll see
a blue progress bar at the bottom of the page. It can be
hard to tell exactly what’s going on and what progress tool is that. To
disable this feature we are going to go up to geoprocessing and Geoprocessing Options and we will uncheck this box here that says background geoprocessing. and what this will do is when we run the tool we will be presented with a dialog which
has more diagnostic information, so this can be
helpful if there are any errors or if we need to
troubleshoot anything. Next up, we are going to enable the
3D analyst extension. This extension gives ArcGIS image processing capabilities. So to do that we go up to
customize and extensions and we will check the box next to 3D analyst. Now, you won’t see any changes here but what it will do is it will enable a number of tool boxes for image and 3D processing. So, before we
convert this TIN to a Raster it’s important to check the
integrity of the file. We want to make sure first
the file is complete that there aren’t any glitches or other errors. We also need to note down a few pieces of
information which will be used later on in the process. So first up, we are going to right-click on our TIN and select Properties and we’ll have a look at the XY coordinate system. Now, in here, we can see that the data is stored in NAD1983 State Plane Arizona Central FIPS 02 02 international feet So, this is using the North American Datum with Arizona State Plane projection and all the TIN data is stored in international feet. You can see here foot 0.3048 During our processing later on, when we are asked to enter distances, cell
sizes and things like that I will be entering those details in
international feet. Let’s have a look at the Z coordinate
system. Now, at the moment there is no coordinate
system to find. So, just by looking at this we can’t tell how the elevation data is stored, whether it is stored in meters or feet or another unit. So to find out what system the elevation data is stored in, we’re going to
have to compare the TIN to another dataset. So to do that let’s open the data up in ArcMap and what I have here is the TIN at the bottom and world elevation contours. This file is supplied by ESRI as a free dataset and it contains large scale contours covering the whole world. So, if we check this later on and this is going to take a little while to draw,
so, we will go to properties and disable the shaded areas and that way it will ArcMap will only show the edge lines
which have been used to create this dataset. So, those edge lines are drawing now and once that’s done the contour layer will also be shown. OK that’s finished drawing. We don’t have
too many contours in this area This data is near Tucson Arizona. We do have one contour line up the top here So, we can compare the TIN data to the existing contours. So, if I look at the properties for this
contour line we can see that it is 600 meters and if I have a look at the properties for one of the TIN edges we can see that the elevation is 2055 Now, because one meter is roughly 3 feet I can look at this and see that the
contour data is in feet. Now that we know the Z coordinate system of the data we can have a look and see if there are
any other areas that need to be fixed so, I am going to turn on the elevation field. and already we can see a problem as we saw before the red edge lines they only extend along here, but ArcGIS has interpolated this area in between. ArcGIS uses a convex hull when creating TIN datasets so what that means is any of these areas will be filled in. Now, this is the problem that needs to be fixed
before we convert to a raster dataset or else this area will be transferred across
to the raster elevation. So, what I am going to do is open up the delineate TIN data area tool and what this does is it tells ArcMap what areas should be filled in,
what areas should be interpolated and which areas should be left out
of the TIN data. Now, this can be performed in
either ArcMap or ArcCatalog. I am going to use ArcMap so that we can see the results in real time. So, open up the search dialog box and select tools and type in delineate TIN data area and as you can see Arc has
already completed so, select that and click
on the delineate TIN data area label, which will open up the tool so there are three options here First is the input TIN, which is the one
we have on screen so, you can either click this Browse
button or click and drag across from the table of
contents Next up, we have the maximum edge length This is the length of TIN edges that ArcMap will exclude
from interpolation TINs are usually made up of small triangles and premise of this tool is that any TIN triangle that has an extremely long edge is probably an error. There is not set rule for what value to enter in this box. It’ll depend on the the spacing of the TIN edges, the
quality of the input data and things like that So, it might take a little bit of trial and error
to get this right. First up I’ll try 100 feet and see what kind of result that
produces. This last option here the method I will leave as Perimeter_Only That is the only one to remove interpolation on the edges of the data. If for example this data was over a large lake and ArcMap was filling in that lake as an error we could set this to All
instead of Perimeter_Only but we will leave that as is So, click OK and depending on the size of the dataset this might take a little while to run. OK, the delineate TIN data area tool has completed. So, I’ll now click close and see what result we have. Now, already this data is looking much
better but if you have a look in the northeast corner up here,
you can see its removed some legitimate data,
so if I zoom in on that area, you can see that these edge polygons must have had an edge
longer than 100 feet so, ArcMap has gone and removed those
area from the data. To me it looks like we run this tool with too small a maximum edge length so, we will try and run
it again. The delineate TIN data area tool overrides the TIN file each time
it is run so, each time we run it it will remove the effects of the previous time it is run, so we don’t need to run it on a fresh copy
of the dataset, we can just run it again on the same TIN file so, I am going to open the tool up drag TIN file in and this time for the maximum edge
length, we are going to set this to 1000 for 1,000 feet and we will click OK and again this will take a few minutes to run. OK, the tool has finished running and this time the results look much
better. I click close we can see that this time it has not removed these
legitimate areas and if I zoom back out we can see that it has removed most of
the field from this concave area. It has left some data in the corner here. The trouble with this tool is it can be a compromise as to what value you enter in that
maximum length field too small will remove
legitimate data too large will leave areas in that we want to remove but on the whole, I’m quite happy with this so, I think we’ll go ahead and use this data as it is. So, now that we have our TIN file ready to convert, we are going to go ahead and open up the TIN to Raster tool. So, in our search box
which is still open here delete the previous search and enter TIN to Raster and select that from the drop down and we will open up this first entry here TIN to Raster 3D analysts so there are several fields here
that needs to be filled in. First is the input TIN, for that we will drag across open TIN file. The output Raster, this is the output image that will be
generated by this tool. Now, it’s important here to specify a file extension. The file extension that you enter
in this field will determine what format the raster file is saved as. We click browse I am going to name this file elevation.img and that would save this file as an
ERDAS Imagine image. The reason I’m using this file format is it’s fairly robust it’s stored as one
single file rather than a multitude of files and directories that you would have if you saved it as
an ESRI Grid. It also has a very few
file restrictions I can give it any file name that I want. I don’t
have to restrict it to 13 characters like a grid, and the images can be practically unlimited in size whereas, say a TIFF image has
a limit of 2 gigabytes. In the output data type, we want
to leave this as FLOAT. A Float or floating-point image stores decimal information in the file so, rather than elevation data being truncated to say 10 feet, 11 feet, 12 feet saving as a Float, you can have n
values in between for example, 10.5 feet, 11.25 feet, etc. The method field determines how ArcGIS will interpolate the TIN data
for the raster image. There are two methods
available Linear or Natural Neighbors.
For now I’m going to leave this as Linear, and depending on the
results you get you might want to experiment with we are trying out natural neighbors, it can be a little bit of
trial and error but in this case I’m going to leave it
as Linear. The sampling distance sets the pixel size of the image so, from this drop down I’m going to select cell size and delete the value that it
has automatically filled in and enter 10. So this will create a
raster file with 10-foot by 10-foot pixels if you entered one, you will have 1 foot by 1 foot pixels, a 100, a 100 feet by 100 feet
and so on. The Z factor field allows you to convert between different height units, for example I know that this TIN data is
stored in feet so, if I wanted to save the raster data in meters instead of feet,
I will change this from a 1 to 0.3048 because one foot is equal to 0.3048 meters Now, I want to keep this data in feet. So, I am going to change that back to a 1. Now that we have all of these fields entered, we can go ahead click OK to run the tool. Depending on the size of the data, this could take several minutes OK, our tool has finished running, so let’s go ahead and check the results. Now, at the moment, the TIN is drawing
over top of the Raster. So, I am going to uncheck the TIN
from the table of contents and see what we have and it looks like we have a good result. Let’s zoom out OK, we can see that the TIN has been converted successfully to a Raster Now, even though this tool has run correctly, it’s
still a little bit hard to see what the results look like.
Most of the Raster is currently colored, fairly consistent grey color. So, let’s go ahead and change
the symbology to give this image more contrast. So, I am going to right-click on the elevation Raster and select Properties and under the Symbology tab I’m going to change the Color Ramp from this drop down here and select this one here which has a wide variety of colors, so it should give a fairly large amount of contrast to the image. I’m going to check the use hillshade effect box
and what this will do it will give the image a 3D effect. It will highlight one side of the mountain and
give a shadow to the other side. These settings, they don’t modify the elevation image that we have just created.
They only change how it is displayed in ArcMap, so if we go ahead
and close ArcMap after this the image will be unmodified. So, let’s click OK and we can see a lot more detail in
this image now. You can make out a map in the
middle some drainage lines along here and if we zoom in you can say that this is
quite detailed we can make out different fields roads, drainage lines and other features. So, in this tutorial, I have shown you how to
convert a TIN dataset to an elevation Raster. We’ve looked at a few considerations and pitfalls and we looked at how to modify the TIN data so that only correct areas are included in the output dataset. Thanks for watching!

Leave a Reply

Your email address will not be published. Required fields are marked *