Nowadays, it’s common to find great orthophotos and satellite imagery on the Web. However, after downloading these (sometimes) large files, you might find that some don’t have any georeferencing. Most likely these files are in an image format supported by Adobe Photoshop(e.g. JPG or TIF) and you can georeference it using the Geographic Imager Georeference tool.
These are the requirements to georeference an image:
Knowing the coordinate system of the image (e.g. Mercator projection, State Plane system Alabama East, UTM system NAD 83 Zone 17 N..etc)
Finding three or more points from the image to assign coordinate values to each of them. These points are known as ground control points.
The first thing you need to know is the coordinate system or projection of the image you are georereferncing. If you are unsure about which coordinate system the image uses, contact the data provider or search the metadata of the image on the Internet. If you cannot get the information of the coordinate system assigned to the image, you might want to try georeferencing with different coordinate systems to make the map as precise as possible.
The second requirement is working with the ground control points. One ground control point consists of several values: 1) Pixel X coordinate, 2) Pixel Y coordinate, 3) Ground X coordinate (e.g. longitude), and 4) Ground Y coordinate (e.g. latitude). Furthermore, to make georeferencing easier, ground control points must be clearly identifiable in the image. Cultural features such as road intersection, a sharp corner of a lot or boundary are good examples of locations used as ground control points.
Now that you know what you’ll need, we’ll demonstrate a georeference workflow using the Geographic Imager Georeference tool and Google Earth.
Step 1: Obtain a non-georeferenced image
This image is in JPEG format and there is no georeference information associated with it. In order to transform it to another coordinate system or projection, mosaic with other images, or align the image to vector work using MAPublisher for Adobe Illustrator, the image must first be georeferenced.
Step 2: Obtain the required information
As indicated above, two key pieces of information are required to georeference an image: a) the coordinate system of the image and b) defining ground control points
a) The coordinate system of the image
The image, collected from Google Earth, is projected in a coordinate system called WGS84 / Pseudo Mercator (this projection is common to Web based mapping systems and is also known as Web Mercator or Google projection).
b) Defining ground control points
We’ll need to define at least three ground control points for georeferencing. Below are the steps for finding out one of the ground control points.
On the non-georeferenced image, decide which spot to use as a point of reference. It should be available on Google Earth where you’ll find the X,Y coordinate values. For the first point, we’ll use the corner boundary between the pavement and a golf course.
Using Google Earth, find the exact same spot as the one decided in the non-georeferenced image. Place a point symbol to help identify the coordinate values. Record the collected latitude and longitude values. The latitude and longitude values are at the centre of the point symbol in the Google Earth window.
Find the coordinates of two additional ground control points. The latitude and longitude values are in decimal degree format and the coordinate system of those values are in the geodetic system “WGS84”.
Step 3: Georeference in Geographic Imager
In Geographic Imager, click the Georeference tool button in the Geograhpic Imager main panel (or choose File > Automate > Geographic Imager : Georerence). The Georeference dialog box will open.
First, we’ll need to set the proper image coordinate system and input coordinate system (the information from Step 2a). In the Format section, click the blue “Specify” link to open the Input Format dialog box.
Here we’ll specify two parameters: Image Coordinate System and alternate input coordinate system. The image of the coordinate system is WGS84 / Pseudo-Mercator as found at Step 2a. Click the “Specify” button to find the coordinate system from the coordinate systems list.
The option “Use alternate input coordinate system” will not have to be selected if the X,Y coordinate values are collected in the Eastings/Northings in the WGS84 / Pseudo-Mercator coordinate system. When those latitude and longitude values are collected, those values are collected in the decimal degree format and the values are in degree in WGS84. We will use those latitude and longitude values for the georeferencing. Specify the destination coordinate system as WGS84.
When the settings are made, click OK to close the Input Format dialog box. All the selected coordinate system for each setting will be indicated in the Format section of the Georeference dialog box.
The next step is to enter the three ground control points collected from Google Earth. Click the pencil tool at the top of the Georeference dialog box and click a point for one of the ground control points collected at the previous steps .
As soon as one point is clicked on the preview image, it will add one row in the Georeference table. This row contains the point name, PX (Pixel x coordinate), PY (Pixel y coordinate), WX (World X coordinate), and WY (World Y coordinate).
For WX and WY, enter the longitude and latitude, respectively, for the first ground control point.
Repeat the same steps for the second and third ground control points.
As soon as you enter three points, Geographic Imager will display the residual error values on the table for the accuracy assessment.
A residual error is the computed difference between an observed source coordinate and a calculated source coordinate. It is the measure of the fit between the true locations and the transformed locations of the output control points. A high residual error indicates possible error in either the observed source coordinates or the reference coordinates of the reference point in question.
When the error is particularly large, you may want to remove and add control points to adjust the error. As a general rule, apply several different transformation methods, select/deselect questionable points and select the method and reference points that yield the minimum residual error, assuming that the defined reference points are correct. Residual values are calculated via the associated error values between computed values and entered values through either the affine or various polynomial methods.
Once completed, the Geographic Imager main panel will indicate the georeference information of the image. Don’t forget to save the file once it is complete. Now your image is ready for any Geographic Imager function. You can also bring this image into MAPublisher for Adobe illustrator and align it to other GIS data.
MAPublisher 8.4 introduces two new related features: to import supported image formats directly from the MAPublisher Simple and Advanced Import dialog boxes and the Image MAP Layer feature type. To import a georeferenced image into the current MAPublisher 8.3 (and earlier) requires you 1) to create a new MAP Layer for an image to be placed, 2) use File > Place to place an image into the Adobe Illustrator document, and 3) to use MAPublisher Register Image to align with the vector work. With MAPublisher 8.4, these steps are streamlined and it will be much simpler to deal with georeferenced image files.
Below is the Simple Import dialog box. The new Format option, Image, is added to the drop-down list. Supported images include: PNG, JPG, TIF, GIF, JP2, PSD, PDD, and BMP.
The VancouverDowntown.tif file was selected from the MAPublisher Quick Start dataset. The source coordinate system of the image, “NAD 83 / UTM Zone 10N”, is automatically detected because it is a GeoTIFF and contains the georeference information of the image.
When the georeferenced image is imported by MAPublisher, it is stored in a new layer called “VancouverDowntown_image”. MAPublisher 8.4 introduces a new MAP Layer feature type called “Image”, a purple icon with the letter ” I “. From now on, all images should be placed on Image MAP Layers.
Remember that images placed in Adobe Illustrator using MAPublisher cannot be transformed or reprojected into another coordinate system. To transform an image from one coordinate system to another, it must be done using another software such as Geographic Imager.
MAPublisher 8.4 will be released very soon. Thanks for sending us feature requests like this one. If you have any feature requests for MAPublisher, Geographic Imager or PDF Maps, please feel free to drop us a line at support@avenza.com. We’re always happy to hear from you!
If you haven’t read about it yet, USGS topographic maps for the United States are now available for download on the Avenza PDF Maps Library.
USGS topographic maps are great for viewing, reference and recreational uses such as hiking, fishing or exploring. You can download the maps beforehand (in cellular range or over Wi-Fi) and use the GPS capability (of the iPhone and iPad Wi-Fi+3G) to locate yourself on the map. These 1:24,000 scale maps include the lower 48 states, Alaska, Hawaii and the District of Columbia. All of the maps are in geospatial PDF format. Best of all, majority of the maps are lightweight meaning they download and process quickly on your device.
The process of getting USGS maps on your iOS device is simple
First, download and install the app if you don’t have it yet. Open the PDF Maps app. In the map list screen, tap the + button (Add Map) in the top-right corner.
Then tap the From Avenza PDF Maps Library button.
The app connects to our PDF Maps Library server and lists several categories. Tap the USGS Topographic Maps category.
The maps are categorized by state and area. We’ll retrieve a topographic map of a part of the city of Tucson, AZ. In the list of the U.S. states, tap Arizona.
In the preview map of Arizona, area grids are represented by the dashed gray lines. These area grids contain all of the available topographic maps categorized further by area name. Tap the area grid that contains Tucson.
Scroll down the list and tap Tucson East. This will take you to a preview of the map before the last step of downloading it.
A preview of the map is shown. Finally, tap the Download 3.3MB button to download the Tucson East map. The PDF file size is listed as 3.3 MB.
The device automatically returns to the PDF Maps app where the Tucson East map will be downloading. After the download is complete, the app will automatically process and render all the tiles you’ll need to explore the map. This will only take a few minutes.
When the processing is completed, it will show it’s total size (18.1 MB) that includes tiles for all of the different zoom levels. Tap the Tucson East map to load it.
These USGS maps and other maps on the Avenza PDF Maps Library are fully georeferenced and compatible with PDF Maps. Still have questions about PDF Maps? Read our support page or send us your questions. Stay tuned for more content.
The upcoming release of MAPublisher 8.4 introduces many new features. One of the new features is called Join Areas. We have received a lot of requests from our customers to create area objects by merging common attribute values. This geoprocessing function is generally known as “dissolve”.
The picture below shows polygon objects from a USA Counties layer. The goal is to create a layer with state boundaries and summing the population count by joining the objects of the counties layer.
In the MAP Attributes panel of the USA Counties layer, every object of the counties layer contains attribute information including county name, state name, FIPS codes, area in km2, population and so on. We’ll be using the StateName attribute value to combine all the county polygons into one polygon per state.
This is the new Join Area dialog box. On the left side, we’ll specify 1) target layer, 2) destination (output) layer, 3) join type and 4) join method. We are trying to create state boundaries from the counties target layer so we’ll select a join type based on the StateName attribute and output it to a new layer called USA States. The join will create compound paths and since our goal is to create state polygons, we’ll dissolve borders between adjacent sub-areas.
On the right side of the dialog box are attribute value operations available for each column. These operations determine what kind of the values will result for every attribute and the operations available are different for each data type (String, Real, Integer). The screenshot below shows the attribute value operation set to Sum for Population attribute (Integer data type). When the Join Area is complete, each state polygon will have the sum of the population of all the counties that belong to it.
After running the Join Areas function, county polygons are dissolved into state boundaries.
The population values show the total sum from all the counties for every state.
This is just one example of how Join Areas can be used. It was initially a feature request and with some discussion and planning, it became real. If you have any feature requests for MAPublisher, Geographic Imager or PDF Maps, please feel free to drop us a line at support@avenza.com. We’re happy to hear from all of you!
When transforming a world image, there may be artifacts created by the Geographic Imager transformation engine. Below are the results of a WGS84 world image transformed into a Stereographic projection.
When we zoom into the problematic area, you can see up close how some artifacts affect the image after the transformation was performed.
To solve this issue, we are introducing a new projection method called Maximum: World Projection in Geographic Imager 3.2.
We are going to use the same world image used with the previous example and transform it into the stereographic projection. Take a close look at the Advanced Options.
Under the Performance/quality section, select Maximum / World Projections from the Precision drop-down list and click OK.
Below is the result of the transformation with the new method available in Geographic Imager 3.2.
Let’s take a close look at the same area where the problem happened with the previous version of Geographic Imager. Now the transformed image does not contain any artifacts.
This option is available since Geographic Imager 3.2. The official version of Geographic Imager 3.2 is available now.
One of the great advantages of using Adobe Illustrator for a mapping project is that you can make great line styles easily. For example, to make a double line stroke and one of them is dashed:
Double strokes are a line graphic style where two different line strokes overlap each other. For example, the image shows that there is a stroke with a brown color and its stroke size is 3 pts. On top of this brown line, there is a 1 pt white dash line:
You might have an experience where you duplicated one line layer and assigned a different style for lines in each of those layers. However, this has some disadvantages. The file size will increase because all the line segments as well as the attribute information attached to every line object is duplicated. Also, when you apply the double stroke line to road layer, the white dash line does not intersect nicely at every intersection of the map:
With Adobe Illustrator CS5, these problems are solved.
0) Create a graphic style like the one shown above.
1) Open the Pathfinder panel (Window > Pathfinder).
2) Select all the line objects in the line layer.
Click the outline tool .
This function in the Pathfinder tool breaks lines at every intersection.
All the selected objects which were selected at Step 2 will be broken into segments at every intersection and they will be grouped as one object in the layer.
3) Having the grouped objects selected, apply the graphic style with the double stoke.
4) The white dashed line is intersected at every intersection nicely.
Quick tip
When creating double stroke, make sure to select the option “Align dashes to corners & path ends, adjusting length to fit” available next to the dash line option.
Note
Since this operation involves a pathfinder functions, the attribute information will not be matintained after the “outline” function is applied to those selected line works. Our development team is looking for a possible solution to keep the attribute information for the future version of MAPublisher.
Here we have placed point symbols for a MAP Point layer. However, we want to change the point angle using the Attribute values.
Below is the attribute table for the point data shown above. The field directionAngle is the field containing the symbol rotation value. With MAPublisher, it’s possible to assign this value to every symbol in this layer.
Open the Edit Schema dialog box from the MAP Attribute panel. Find the field called #Rotation from the attribute field list. This #Rotation field is hidden/invisible by default. Click the Visible option to enable it and click OK.
In the MAP Attributes panel, you can see that the #Rotation field shown. The values in this field is 0.00 degree for every point in the layer. We’ll assign the angle value from the directionAngle field to the #Rotation value .
Open the Apply Expression dialog box from the MAP Attributes panel. Enter the column name directionAngle for the Expression and ensure that the value will be applied to the field #Rotation.
Every value from the directionAngle field is now inherited by the #Rotation field.
As a result, the rotation angle is now applied to every point.
The origin of the rotation is at each point’s registration point. With Adobe Illustrator CS4 and earlier, the registration point is set at the centre of the point symbol. With Adobe Illustrator CS5, the registration point can be flexibly placed. This will be discussed with some examples in a later topic. Stay tuned!
When transforming a world map in a geodetic system (such as WGS84) to a predefined projection (such as Robinson) using MAPublisher, the central meridian of the predefined projection should be set to 0 degree longitude as shown below.
Image 1: world map in WGS84
Image 2: world map in a predefined Robinson Projection
However, you might want to have a map with a different region centred on your map. For example, Image 3 below shows a world map with a part of Asia centred. In this case, the central meridian was set to 160 degrees East.
Image 3: world map in a custom Robinson Projection with a central meridian value set to 160 degree East
Today we’ll introduce how to create a custom coordinate system by modifying a predefined coordinate system. We’ll use an example using a GIS dataset world.mif available in the MAPublisher Tutorial folder. We are going to transform a world map to a custom central meridian value with the Robinson projection.
Step 0 : import the “world.mif” file from MAPublisher tutorial folder.
Step 1 : Open the MAP View Editor window from the MAP Views panel.
In the MAP View Editor window, you can see that the scale of the map, position of the map extent with respect to the current document extent, and most importantly the current coordinate system assigned to the MAP View.
We are going to transform the MAP View from WGS84 to the Robinson projection with a custom central meridian value. Check the “Perform cordinate System Transformation option.
Click the Specify button under the “Perform Coordinate System Transformation” section. It will open the “Specify Destination Coordinate System” dialog box.
Step 2: Creating a custom coordinate system with the Robinson projection
We are going to create a custom coordinate system based on the Robinson projection by modifying the existing Robinson projection. Find the existing Robinson projection from the list.
On the left side, navigate to Coordinate system > Projected > World. Highlight the folder “World”. You will see the list of the predefined coordinate systems available on the right side of the window. Find the “Robinson” and highlight it.
Once the predefined Robinson projection is highlighted, click the Copy button at the bottom. It will duplicate the existing coordinate system and will open the “Projected Coordinate System Editor” dialog box for the duplicated coordinate system.
In the Projected Coordinate System Editor dialog box, there are two tabs: Identification and Definition. In the Identification tab, enter a new name for this customer coordinate system. This name will be used when you are searching the object.
Click the Definition tab. Change the value of central_meridian from 0 (default) to 160. Click OK to apply this new setting. You have just made a custom coordinate system based on the existing Robinson projection.
Step 3: Complete the Transformation
Under the “Perform Coordinate System Transformation”, the new custom coordinate system just created is indicated. Now you are ready to transform your map.
Now the world map is successfully transformed into the custom coordinate system (Robinson with the central meridian set to 160 degree East).
You might want to take a look at this other blog about the new transformation engine implemented in MAPublisher 8.3.
Transforming an image into a custom coordinate system with Geographic Imager
You can use the same approach to transform your image into a custom coordinate system.
First, we open a world image that has a WGS84 coordinate system.
Click the Transform button in the Geographic Imager main panel. It will open the Transform dialog box.
Click the Specify button. Now repeat Step 2 illustrated above to create a custom coordinate system. Once you select the custom coordinate system in the “Specify Coordinate System” dialog box, it will be indicated in the Transformation dialog box (in the example below, a custom coordinate system “Robinson cm @ 160 degree East” is selected as a destination coordinate system).
As soon as you click the Transform button, the transformation process will start. Once the transformation process is completed, the Geographic Imager main panel will indicate the new custom coordinate system name.
MAPublisher offers a variety of labelling options, ranging from the MAP Tagger tool used for hand labelling single pieces of art, the Label Features tool for automatic attribute labelling, and MAPublisher LabelPro™, a separately licensed advanced labelling engine.
MAPublisher LabelPro ships with nearly 100 highway shields from across North America into which attribute labels can be easily placed. Although LabelPro does not support adding custom symbols to its existing symbols library, the following instructions outline a manual method for adding a custom highway shield to your map, along with placing text on to this shield.
First we must setup our custom shield. This can be drawn in Adobe Illustrator, or produced from a pre-existing image brought into Illustrator using the File > Place menu option. For this exercise I have taken a highway shield I found online from York Region Ontario, and using Adobe Photoshop removed the highway number from the shield.
Once the shield is drawn and sized appropriately and placed in Illustrator, simply use the Selection Tool to drag the symbol into the Adobe Illustrator Symbols panel. Be sure to name the symbol, as you will need to access the symbol from a list later on; I named mine “York_Shield”
Our next step is to produce our feature labels. Using the Label Features tool, choose to label with the “Don’t follow line, create point text” option selected. Once the labels are placed on the map, use the Adobe Layers panel to select the labels and use the Paragraph panel or the Control Toolbar to centre justify the labels. This step is important for easily lining up our shields with the labels.
We now need to create a point layer with a point corresponding to each label. This is easily done by using the MAP Attribute panel option menu to “Export Attributes..” of our newly created Feature Labels MAP Text Layer. Be sure to choose export all attributes under Options: Scope, and to check “Include column names on first line” as we will be using the hidden MAPX and MAPY attribute columns when importing this data back into the map as point data.
Next, use the MAPublisher Simple Import tool to add the newly created .csv file of referenced attribute information. When prompted by the Settings dialog, choose the MAPX column as the column containng X coordinates, and MAPY for Y coordinates. Once the data is imported, if it has not been added to the MAP View containing your line and text layers, add it, and specify the coordinate system if necessary.
With the imported point data selected, open the MAP Attribute panel and right click a column heading to access the Show/Hide Columns > Show All option. double click the #Style column and change the style to your shield symbol. Use the Apply Expression tool in the option menu to apply the symbol to every item at once.
Alternately, a MAP Stylesheet can be built to apply the symbol only to art with a specific range of attributes. In the Adobe layers panel move your label layer above your symbol layer.
If text and symbol do not line up as desired, the symbol geometry will need to be altered. If you are using CS5, doubble click the shield in the symbol panel to enter isolation mode, here you can drag the symbol to respecify the anchor point so that your symbol lines up as you would like it. If you are using CS3 or CS4, you will need to add some invisible art (no stroke/no fill) just below or above the symbol to adjust its extents, and where exactly the symbol’s centre point is located. As well, symbol and text rotation can be edited globally by changing the #Rotation attribute in the MAP Attributes panel.
If your workflow involves Terrain Shader, specifying a DEM schema is an important step, especially when dealing with mulitple DEM files.
When importing a single DEM file, Geographic Imager converts elevation values to gray scale values. For example, if the elevation range in your DEM file is between 0 and 2500 meters and the “Auto-stretched” option is selected, this range will be converted to the Adobe Photoshop gray scale range between black and white. As shown below, the black color is assigned to the lowest elevation value (0 meter) while the white color is assigned to the highest elevation value (2500 meters). For elevation values between 0 and 2500, Geographic Imager calculates and converts them into gray scale.
In this example, we’ll use six DEM files of one geographic region. Many datasets are distributed as tiled DEM files. Each of them is next to each other and the goal is to create a colorized DEM image from those six files.
When dealing with multiple DEM files, you will need to consider the elevation range of the each DEM file. In other words, the elevation range in each DEM file will be slightly different.
Option 1: Using the “Auto-Stretched” option for multiple DEM files
When importing multiple DEM images and using the “Auto-stretched” option, click “Apply to All”…
Every one of the DEM images will be converted to the gray scale between black and white.
As a result, you can get the maximum contrast in each image. However, you will not be able to mosaic or apply Terrain Shader to those six images because each DEM has slight differences in elevation and an all encompassing schema like the”Auto-stretched” option will not work.
Option 2: Creating a DEM schema by specifying a range
In order to apply Terrain Shader to multiple DEM files, you will need to assign one DEM schema to each DEM image you would like to share the same schema.
Step 1: Identify the elevation range amongst multiple DEM files
Explore the DEM files and find out what the elevation range is for each one. Then note which are the lowest and highest values among all DEMs. For this example, the lowest elevation is 0 m and the highest is 3,231 meters.
Step 2: Create a new DEM schema for your dataset
Choose File > Open and select multiple DEM files. Once the Import DEM file dialog box is open, click the Add button to open the “Edit DEM Schema” dialog box.
Create a new Schema name (e.g. “my study area”). Simply enter the lowest and highest elevation value found in Step 1.
Step 3: Apply the DEM schema to your datasets
When you’ve created a new DEM schema, it will be available in the “Select Schema” drop-down list. Choose the new schema and click “Apply to All”. This selected schema will be applied to all the DEM files being imported.
After the import process is completed, the images are ready for Terrain Shader.
When one of the imported DEM file is the active document, click the “DEM” tab in the Geographic Imager panel. It shows the DEM schema name, the DEM value range, and the actual elevation value available in the currently active document. Click the “Calculate” button if you do not see the statistics (actual elevation value range of the active document).
Step 4: Apply Terrain Shader to your DEM files
Since each DEM has a schema, a mosaic can be perfomed and then Terrain Shader can be applied to the mosaicked iamge.
in the Google Earth window.
in the Geograhpic Imager main panel (or choose File > Automate > Geographic Imager : Georerence). The Georeference dialog box will open.
.
.
“Align dashes to corners & path ends, adjusting length to fit” available next to the dash line option.
at the bottom. It will duplicate the existing coordinate system and will open the “Projected Coordinate System Editor” dialog box for the duplicated coordinate system.
