# XORIG, YORIG : cell center or cell edge?

**URL:** <https://forum.cmascenter.org/t/xorig-yorig-cell-center-or-cell-edge/2336>\
**Category:** SMOKE\
**Created:** [May 14, 2021, 5:49am UTC](https://forum.cmascenter.org/t/xorig-yorig-cell-center-or-cell-edge/2336 "2021-05-14T05:49:24Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![gwangjin](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.cmascenter.org/gwangjin/32/1336_2.png) [@gwangjin](https://forum.cmascenter.org/u/gwangjin)\
**Post date:** [May 14, 2021, 5:49am UTC](https://forum.cmascenter.org/t/xorig-yorig-cell-center-or-cell-edge/2336/1 "2021-05-14T05:49:24Z")

</div>

Hello,

I have a simple question regarding ‘XORIG’ and ‘YORIG’ in GRIDDESC.  
Does ‘XORIG’ and ‘YORIG’ mean cell center or cell edge when emission output are treated as cell center value?

I’m not sure which type I should use for grid (cross or dot).  
(I am trying to obtain cell center emission for WRF-Chem model. And I would like treat emissions as cell center values.)

Thank you.

![GRIDS](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/d/de7ffecd3909a7dd8fc8da839089474dda0421db.jpeg)

---

<div class="post-metadata">

**Author:** ![cjcoats](https://avatars.discourse-cdn.com/v4/letter/c/ac8455/32.png) [@cjcoats](https://forum.cmascenter.org/u/cjcoats)\
**Post date:** [May 14, 2021, 11:24am UTC](https://forum.cmascenter.org/t/xorig-yorig-cell-center-or-cell-edge/2336/2 "2021-05-14T11:24:04Z")

</div>

From probably the same page you got this diagram – [https://cjcoats.github.io/ioapi/GRIDS.html#horiz](https://cjcoats.github.io/ioapi/GRIDS.html#horiz):

- X\_ORIG is the X coordinate of the grid origin (lower left corner of the cell at column=row=1), given in map projection units (meters, except in Lat-Lon coordinate systems).
- Y\_ORIG is the Y coordinate of the grid origin (lower left corner of the cell at column=row=1), given in map projection units (meters, except in Lat-Lon coordinate systems).

---

<div class="post-metadata">

**Author:** ![gwangjin](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.cmascenter.org/gwangjin/32/1336_2.png) [@gwangjin](https://forum.cmascenter.org/u/gwangjin)\
**Post date:** [May 16, 2021, 1:14pm UTC](https://forum.cmascenter.org/t/xorig-yorig-cell-center-or-cell-edge/2336/3 "2021-05-16T13:14:50Z")

</div>

Thank you for your comment.

---

<div class="post-metadata">

**Author:** ![jwilson](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.cmascenter.org/jwilson/32/2297_2.png) [@jwilson](https://forum.cmascenter.org/u/jwilson)\
**Post date:** [June 13, 2022, 6:46pm UTC](https://forum.cmascenter.org/t/xorig-yorig-cell-center-or-cell-edge/2336/4 "2022-06-13T18:46:04Z")

</div>

Piggy backing off this with a C-LINE question: the tool gives a point output that correlates to a raster. Do those points represent the bottom left corner of each cell or the center?

---

<div class="post-metadata">

**Author:** ![cseppan](https://avatars.discourse-cdn.com/v4/letter/c/6de8d8/32.png) [@cseppan](https://forum.cmascenter.org/u/cseppan)\
**Post date:** [June 20, 2022, 10:05pm UTC](https://forum.cmascenter.org/t/xorig-yorig-cell-center-or-cell-edge/2336/5 "2022-06-20T22:05:52Z")

</div>

In C-LINE, the points are the receptor locations where the concentrations are modeled. These concentrations are used to generate the overlay image, with different approaches used for short-term vs. long-term (annual) results.

When viewing the results from computing short-term concentrations, each “block” in the overlay image would be centered around a receptor (the exact number of pixels in each “block” varies depending on the modeling domain). For long-term concentrations, the receptor concentrations are interpolated, so the receptor location doesn’t correspond to particular pixels.