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Lidar data extents

CraigBarrett

Hi,

My LIdar data is inserting at the extents shown below which is in meters although the XY Linear Unit shows Feet (See below)

The Statistics on the LAS file shows the correct extetns but shows the XY Linear Unit as Meters (see below)...any ideas why would be helpful

Thanks,

Craig

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Accepted answers

CraigBarrett

Hi Gabriel,

Thanks, that's a lot of good information. I determined the LAS is project to State Plane meters and after doing some digging last night I found this nice little tool http://www.arcgis.com/home/item.html?id=d8782286e3c9442bb5c244bf39da5966 - LAS Dataset tools. It has a script in there to Define LAS Projection and changes the current projection to one specified. I added the LAS file and changed it to Florida State Plane feet and it created a .prj file. This was enough to get the LAS into feet and agree with the LASD file and data frame. It finally came in correctly (see below).

Thanks for your pointers to get me thinking in and looking in the right direction!

Thanks,Craig

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CraigBarrett

Hi Gabriel,

Thanks for your pointers to get me thinking in and looking in the right direction!

Thanks,Craig

GabrielUpchurch1

Thanks for the update. Before we can explore projecting the data to State Plane Feet, there is some additional factors we need to consider:

1. Did you get this data directly from the vendor? The reason I ask is because the vendor may have made a mistake or someone in possession of it after delivery by the vendor may have altered the spatial reference or its definition. The metadata reports it should be in feet so you may just be able to go straight to the vendor and point this out. Alternatively, if you got it from a third-party, you may have to address it yourself.

2. The next question is if the LAS file is projected correctly? What I mean is whether the LAS file was projected to State Plane Meters or if the spatial reference definition was somehow altered accidentally to report that the linear unit is meters (when it is actually feet). If it is the former, you will need to project the LAS file to State Plane Feet and if it is the latter, you need to correct the spatial reference definition. Both should be doable but you first need to identify which scenario is in play. To do this, set the PCS of the LAS Dataset to the same PCS that is reported for the LAS file (State Plane Meters). In a blank map document, add some reference data that you know is spatially accurate for the area of interest. An Esri basemap will do if you don't have anything else you would prefer to use. After adding the reference data, add the LAS Dataset to the map document. If the LAS Dataset shows up in the correct location with the correct extent when compared to the reference data, then you know the LAS file is actually projected in State Plane Meters. If the LAS Dataset is in the wrong location (the misalignment should be considerable between feet and meters), then you know it is the projection definition that is incorrect. Note: If you see a slight misalignment, it could be that you need to specify a transformation under the Coordinate system tab of the Data Frame Properties (or that there just isn't perfect agreement between the LAS file and the reference data).

Once you have determined which scenario you are encountering with the LAS file, let me know and we can identify the best approach to take to remedy the issue. Also, let me know which version of Desktop you are using since this will impact what options are available to you.

CraigBarrett

Hi Gabriel,

Thanks for the reply!

The PCS info does show Meters (See below). I'm a little confused how I can show the layer in State Plane Feet instead. Any ideas?

Thanks,
Craig

GabrielUpchurch1

Hi Craig,

Looking at the screenshots you provided, the extents reported in both dialogs are very similar. The LAS Dataset is reporting the extent in feet and the LAS File Properties is reporting it in meters. If you convert the extents reported by the LAS Dataset from feet to meters, the resulting values are very close to what is reported in the LAS file's properties. Since we know you have specified the LAS Dataset's PCS to be in Florida State Plane Feet, then my initial guess would be that the PCS of the actual LAS file is really in Florida State Plane Meters (even though the metadata says it should be feet).

Have you hit the plus sign beside "Spatial Reference" entry in the LAS File Properties dialog to review the full PCS info? The screenshot only shows the first part of the PCS name.

CraigBarrett

Hi Ian, thanks for the reply.

I have the LASD set to the following:

The metadata for the LAS shows the following:

Looks like they are both in agreement but, it is still
displaying at the wrong extents.

Any thoughts?

Thanks,
Craig

IanMurray

The first one is the extent and units of the Las Dataset (.lasd) you imported the las files into. The second is the extent and units of the particular las file.

Is the lasd in the same spatial reference as the las file?

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